Abstract
Background:
Several studies have shown that anti-dsDNA and anti-Sm antibodies not only contribute to the classification of systemic lupus erythematosus (SLE) but also strongly correlate with disease activity. However, the relationship between double positivity for anti-dsDNA and anti-Sm antibodies and disease activity remains unclear.
Objectives:
This study aimed to assess the clinical significance of double positivity for anti-dsDNA and anti-Sm antibodies in SLE.
Design:
A single-center retrospective study was conducted, consecutively enrolled hospitalized patients with SLE who underwent anti-dsDNA and anti-Sm antibody testing between June 2009 and December 2022.
Methods:
In this study, clinical data were collected from the electronic medical records of all study participants. SLE Disease Activity Index 2000 (SLEDAI 2000) scores were calculated; SLEDAI 2000 scores excluding anti-dsDNA scores were defined as modified SLEDAI 2000 (mSLEDAI 2000) scores. Severe disease activity was defined as a SLEDAI 2000 score of >12.
Results:
The study included 408 patients with SLE; of them, 95 were double-positive for anti-dsDNA and anti-Sm antibodies, 193 were single-positive for anti-dsDNA or anti-Sm antibodies, and 120 were double-negative. The double-positive group showed more clinical manifestations, lower C3 and C4 levels, and higher SLEDAI 2000 and mSLEDAI 2000 scores compared to the double-negative and single-positive groups. During follow-up, double-positive patients, whether converted to single-positive or double-negative, showed a significant decrease in SLEDAI 2000 and mSLEDAI 2000 scores, but the improvement in SLEDAI 2000 scores was not significant in patients with persistent double positivity. In recognizing severe disease activity, double positivity had the highest specificity, positive predictive value, positive likelihood ratio, and highest Youden index, albeit with the lowest sensitivity, compared to anti-dsDNA positivity, anti-Sm positivity, and positivity for anti-dsDNA and/or anti-Sm antibodies. Furthermore, a higher proportion of patients with double positivity were treated with high-dose or shock-dose glucocorticoids.
Conclusion:
Double positivity for anti-dsDNA and anti-Sm antibodies suggests higher disease activity in patients with SLE who may require more intense immunosuppressive therapy.
Keywords: anti-dsDNA antibodies, anti-Sm antibodies, disease activity, systemic lupus erythematosus
Introduction
Systemic lupus erythematosus (SLE) is a common autoimmune disease with multiorgan involvement. 1 The abundance of autoantibodies in serum is a typical clinical feature of SLE, of which anti-dsDNA and anti-Sm antibodies are the hallmark antibodies and have been included in several classification criteria for SLE.2 –4
In addition to their use in classification, anti-dsDNA antibodies are involved in the pathological process of SLE and are closely associated with damage to vital organs, especially the kidneys.5,6 Moreover, numerous studies have reported that anti-dsDNA antibodies are closely associated with SLE disease activity, and elevated anti-dsDNA antibody titers may signal SLE flare-up or exacerbation.7 –9 Therefore, monitoring anti-dsDNA antibodies plays a crucial role in the diagnosis, disease assessment, and decision to treat SLE. Most clinical practices use anti-Sm antibodies as an essential reference index for diagnosing SLE; however, some studies have confirmed that anti-Sm antibodies are closely related to the clinical manifestations of SLE.10 –12 Moreover, in new-onset SLE, serum anti-Sm antibody levels are positively associated with disease activity. 13
Therefore, we hypothesized that patients with double positivity for anti-dsDNA and anti-Sm antibodies would have a more severe clinical phenotype and higher disease activity. Although previous studies have addressed this topic, they have been limited to small samples with inconsistent findings.14,15 Moreover, in several previous cluster analyses of autoantibodies associated with SLE, anti-dsDNA and anti-Sm antibodies were mostly classified into different clusters.16 –18 Therefore, this study aimed to investigate the clinical significance of double positivity for anti-dsDNA and anti-Sm antibodies in patients with SLE.
Materials and methods
Study design
This single-center retrospective study was conducted in the Department of Rheumatology and Immunology at the Second Affiliated Hospital of Soochow University. Hospitalized patients with SLE who underwent anti-dsDNA and anti-Sm antibody testing between June 2009 and December 2022 were consecutively enrolled in the study. The reporting of this study conforms to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement. 19
Patients with SLE fulfill at least one of the following three criteria: the American College of Rheumatology (ACR) 1997 revised criteria, the 2012 Systemic Lupus International Collaborating Clinics classification criteria, or the 2019 European League Against Rheumatism/ACR classification criteria.2 –4 Patients were excluded if they had one or more of the following conditions: pregnancy, thrombotic microvascular disease, primary hematological disorders, liver and spleen disease, severe infections, drug-induced myelosuppression, other causes of renal disease (e.g., hypertension and diabetes mellitus), or other connective tissue diseases (e.g., rheumatoid arthritis and systemic sclerosis).
Data collection
The inpatient electronic medical records of all study participants were used to extract information regarding the demographics, treatment, clinical presentation, and laboratory test results, such as blood cell counts, complement levels, and autoantibody profiles, all of which were presented at the time of hospitalization. Based on the above data, SLE Disease Activity Index 2000 (SLEDAI 2000) scores were calculated, and SLEDAI 2000 scores excluding anti-dsDNA scores were defined as modified SLEDAI 2000 (mSLEDAI 2000) scores. In our center, antinuclear antibody (ANA) titers were measured using immunofluorescence antibody assay, and autoantibody profiles, including anti-dsDNA and anti-Sm antibodies, were detected by immunoblotting using EUROLINE ANA Profile (IgG) (EUROIMMUN Medizinische Labordiagnostika AG, Lübeck, Germany). In addition, the levels of C3 and C4 were determined using a commercial kit (Beckman Coulter, Inc., California, USA) by the turbidimetric method.
Leukopenia was defined as a leukocyte count <3.0 × 109/L, neutropenia as a neutrophil count <1.5 × 109/L, lymphopenia as a lymphocyte count <0.8 × 109/L, anemia as a hemoglobin level <110 or <120 g/L for females and males, respectively, and thrombocytopenia as a platelet count <100 × 109/L.
The doses of glucocorticoids used in the same period as the autoantibody profile results were graded. High-dose glucocorticoids were defined as prednisone 1–2 mg/kg/day (>40 and ⩽100 mg/day) or equivalent, and shock-dose glucocorticoids were defined as methylprednisolone 250–500 mg/day. The disease activity of patients with SLE was categorized into two grades based on the SLEDAI 2000 scores: ⩽12 was defined as mild-to-moderate disease activity, and >12 was defined as severe disease activity. 20
Data analysis
Categorical variables were expressed as absolute frequencies and percentages; differences between two groups were evaluated using the chi-square or Fisher’s exact tests, differences among multiple groups were evaluated using the chi-square test, and subsequent comparisons between the two groups were examined using the z-test. Continuous variables were expressed as mean ± SD or median and the 25th–75th percentiles (P25 and P75) according to the Shapiro–Wilk test. For comparisons of skewed variables between two groups, the Mann–Whitney U test was used; for comparisons of skewed variables among multiple groups, the Kruskal–Wallis test was used, followed by the Mann–Whitney U test for comparisons between the two groups. The sensitivity, specificity, accuracy, and Youden index were calculated to analyze the performance of different antibody statuses in recognizing severe disease activity in SLE. The positive predictive value, negative predictive value, positive likelihood ratio, and negative likelihood ratio were also analyzed. The alpha risk was set at 5%, and the p-value was adjusted for the number of two-by-two comparisons when analyzing the differences among multiple groups. Statistical analyses were performed using IBM SPSS Statistics for Windows V.25.0 (IBM Corp., Armonk, NY, USA) and GraphPad Prism V.10.1.2 software (San Diego, CA, USA).
Results
Clinical characteristics of patients with SLE
This study included 408 patients with SLE; 89.7% were female, the median age was 35 (27, 48) years, and the median disease duration was 12 (2, 72) months (Table 1). A total of 243 (59.6%) and 140 (34.3%) patients tested positive for anti-dsDNA and anti-Sm antibodies, respectively. Of these, 95 patients were positive for both antibodies, 148 were positive for anti-dsDNA alone, and 45 were positive for anti-Sm alone.
Table 1.
Clinical characteristics of patients with SLE.
| Variable | Value | N |
|---|---|---|
| Female, n (%) | 366 (89.7) | 408 |
| Age (years) | 35 (27, 48) | 408 |
| Disease duration (months) | 12 (2, 72) | 408 |
| Fever, n (%) | 98 (24.0) | 408 |
| Rash, n (%) | 176 (43.1) | 408 |
| Alopecia, n (%) | 134 (32.8) | 408 |
| Oral ulcers, n (%) | 51 (12.5) | 408 |
| Arthritis, n (%) | 77 (18.9) | 408 |
| Myositis, n (%) | 11 (2.7) | 408 |
| Vasculitis, n (%) | 78 (19.1) | 408 |
| Pleurisy, n (%) | 59 (14.5) | 408 |
| Pericarditis, n (%) | 51 (12.5) | 408 |
| Lupus nephritis, n (%) | 257 (63.1) | 407 |
| Neurologic involvement, n (%) | 28 (6.9) | 408 |
| Cardiac involvement, n (%) | 30 (7.4) | 408 |
| Interstitial lung disease, n (%) | 22 (5.4) | 408 |
| Leukocyte count (109/L) | 4.2 (3.1, 6.4) | 408 |
| Leukopenia, n (%) | 90 (22.1) | 408 |
| Neutrophil count (109/L) | 2.8 (1.9, 4.7) | 408 |
| Neutropenia, n (%) | 39 (9.6) | 408 |
| Lymphocyte count (109/L) | 1.0 (0.6, 1.4) | 408 |
| Lymphopenia, n (%) | 148 (36.3) | 408 |
| Hemoglobin (g/L) | 109 (92, 124) | 408 |
| Anemia, n (%) | 211 (51.7) | 408 |
| Platelet counts (109/L) | 166 (96, 217) | 408 |
| Thrombocytopenia, n (%) | 109 (26.7) | 408 |
| C-reactive protein (mg/L) | 5.9 (5.2, 9.1) | 408 |
| Erythrocyte sedimentation rate (mm/h) | 32.0 (14.8, 52.3) | 394 |
| Antinuclear antibody titer | 1000 (320, 1000) | 406 |
| Anti-dsDNA, n (%) | 243 (59.6) | 408 |
| Anti-Smith, n (%) | 140 (34.3) | 408 |
| Anti-U1RNP, n (%) | 168 (41.3) | 407 |
| Anti-ribosomal P protein, n (%) | 97 (23.8) | 407 |
| Anti-Ro52, n (%) | 212 (52.1) | 407 |
| Anti-Ro60, n (%) | 247 (60.7) | 407 |
| Anti-SSB, n (%) | 65 (16.0) | 407 |
| Anti-centromere protein B, n (%) | 11 (2.7) | 407 |
| Antiphospholipid antibodies, n (%) | 44 (19.0) | 232 |
| Complement 3 (g/L) | 0.550 (0.380, 0.774) | 407 |
| Complement 4 (g/L) | 0.099 (0.064, 0.153) | 407 |
| SLEDAI 2000 scores | 13 (8, 19) | 406 |
| Mild-moderate disease activity, n (%) | 191 (47.0) | |
| Severe disease activity, n (%) | 212 (53.0) | |
| Modified SLEDAI 2000 scores | 12 (7, 18) | 406 |
| High-dose or shock-dose glucocorticoid, n (%) | 222 (54.4) | 408 |
Except where indicated otherwise, values are median (P25, P75).
RNP, ribonucleoprotein; SLE, systemic lupus erythematosus; SLEDAI 2000, Systemic Lupus Erythematosus Disease Activity Index 2000.
Relationship of anti-dsDNA antibodies with clinical manifestations and serological indicators of SLE
First, we investigated the clinical characteristics of patients with anti-dsDNA antibody positivity. Patients with anti-dsDNA positivity had a shorter disease duration, a higher prevalence of rash, alopecia, arthritis, leukopenia, and anemia and a lower prevalence of neuropsychiatric lupus than patients with anti-dsDNA negativity (Table 2). Furthermore, leukocyte, neutrophil, and hemoglobin levels were lower in patients with anti-dsDNA positivity than in patients with anti-dsDNA negativity, while the opposite was true for ANA titers. Moreover, the positivity of anti-Sm and anti-U1 ribonucleoprotein (RNP) antibodies was more common in patients with anti-dsDNA positivity.
Table 2.
Comparison of clinical manifestations and serological indicators between SLE patients with and without anti-dsDNA positivity.
| Variable | With anti-dsDNA positivity | Without anti-dsDNA positivity | p | ||
|---|---|---|---|---|---|
| Value | N | Value | N | ||
| Disease duration (months) | 6 (1, 70) | 243 | 24 (3, 90) | 165 | 0.001 |
| Rash, n (%) | 122 (50.2) | 243 | 54 (32.7) | 165 | <0.001 |
| Alopecia, n (%) | 92 (37.9) | 243 | 42 (25.5) | 165 | 0.009 |
| Arthritis, n (%) | 54 (22.2) | 243 | 23 (13.9) | 165 | 0.036 |
| Neurologic involvement, n (%) | 11 (4.5) | 243 | 17 (10.3) | 165 | 0.024 |
| Leukocyte count (109/L) | 3.8 (2.9, 5.7) | 243 | 5.0 (3.5, 7.2) | 165 | <0.001 |
| Leukopenia, n (%) | 62 (25.5) | 243 | 28 (17.0) | 165 | 0.041 |
| Neutrophil count (109/L) | 2.5 (1.7, 4.0) | 243 | 3.4 (2.2, 5.6) | 165 | <0.001 |
| Hemoglobin (g/L) | 105 (89, 119) | 243 | 113 (98, 128) | 165 | 0.002 |
| Anemia, n (%) | 141 (58.0) | 243 | 70 (42.4) | 165 | 0.002 |
| Antinuclear antibody titer | 1000 (320, 3200) | 242 | 320 (100, 1000) | 164 | <0.001 |
| Anti-Smith, n (%) | 95 (39.1) | 243 | 45 (27.3) | 165 | 0.014 |
| Anti-U1RNP, n (%) | 110 (45.5) | 242 | 58 (35.2) | 165 | 0.038 |
| Complement 3 (g/L) | 0.450 (0.339, 0.644) | 243 | 0.696 (0.483, 0.858) | 164 | <0.001 |
| Complement 4 (g/L) | 0.078 (0.060, 0.129) | 243 | 0.125 (0.070, 0.180) | 164 | <0.001 |
| SLEDAI 2000 scores | 15 (10, 21) | 242 | 11 (6, 17) | 164 | <0.001 |
| Modified SLEDAI 2000 scores | 13 (8, 19) | 242 | 11 (6, 17) | 164 | 0.084 |
Except where indicated otherwise, values are median (P25, P75).
RNP, ribonucleoprotein; SLE, systemic lupus erythematosus; SLEDAI 2000, Systemic Lupus Erythematosus Disease Activity Index 2000.
Regarding disease activity, patients with anti-dsDNA positivity developed decreased C3 and C4 levels and elevated SLEDAI 2000 scores. However, when the scores of anti-dsDNA antibodies were excluded from the SLEDAI 2000 scores, there was no longer a statistically significant difference in mSLEDAI 2000 scores between patients with anti-dsDNA positivity and anti-dsDNA negativity.
Association of anti-Sm antibodies with clinical manifestations and serological indicators of SLE
Next, we explored the association between anti-Sm antibodies and clinical manifestations and serological indicators of SLE. Patients with anti-Sm positivity were younger and had a shorter disease duration (Table 3). Anti-Sm antibodies were positively associated with several clinical and laboratory parameters, including rash, arthritis, vasculitis, lymphopenia, anti-dsDNA, anti-U1RNP, and anti-ribosomal P protein antibodies. Patients with anti-Sm positivity had decreased leukocyte counts and increased ANA titers. As in patients with anti-dsDNA positivity, C3 and C4 levels were markedly low in patients with anti-Sm positivity, whereas the SLEDAI 2000 and mSLEDAI 2000 scores were significantly elevated.
Table 3.
Comparison of clinical manifestations and serological indicators between SLE patients with and without anti-Sm positivity.
| Variable | With anti-Sm positivity | Without anti-Sm positivity | p | ||
|---|---|---|---|---|---|
| Value | N | Value | N | ||
| Age (years) | 32 (26, 44) | 140 | 36 (28, 50) | 268 | 0.021 |
| Disease duration (months) | 6 (2, 36) | 140 | 24 (1, 93) | 268 | 0.006 |
| Rash, n (%) | 80 (57.1) | 140 | 96 (35.8) | 268 | <0.001 |
| Arthritis, n (%) | 38 (27.1) | 140 | 39 (14.6) | 268 | 0.002 |
| Vasculitis, n (%) | 42 (30.0) | 140 | 36 (13.4) | 268 | <0.001 |
| Leukocyte count (109/L) | 3.8 (3.0, 5.6) | 140 | 4.6 (3.1, 6.9) | 268 | 0.210 |
| Lymphopenia, n (%) | 61 (43.6) | 140 | 87 (32.5) | 268 | 0.027 |
| Antinuclear antibody titer | 1000 (320, 3200) | 139 | 320 (320, 1000) | 267 | <0.001 |
| Anti-dsDNA, n (%) | 95 (67.9) | 140 | 148 (55.2) | 268 | 0.014 |
| Anti-U1RNP, n (%) | 101 (72.7) | 139 | 67 (25.0) | 268 | <0.001 |
| Anti-ribosomal P protein, n (%) | 42 (30.2) | 139 | 55 (20.5) | 268 | 0.030 |
| Complement 3 (g/L) | 0.513 (0.328, 0.720) | 140 | 0.590 (0.400, 0.788) | 267 | 0.006 |
| Complement 4 (g/L) | 0.076 (0.060, 0.125) | 140 | 0.112 (0.066, 0.163) | 267 | <0.001 |
| SLEDAI 2000 scores | 16 (10, 21) | 140 | 12 (8, 18) | 266 | 0.001 |
| Modified SLEDAI 2000 scores | 14 (8, 19) | 140 | 11 (6, 17) | 266 | 0.002 |
Except where indicated otherwise, values are median (P25, P75).
RNP, ribonucleoprotein; SLE, systemic lupus erythematosus; SLEDAI 2000, Systemic Lupus Erythematosus Disease Activity Index 2000.
Association of double positivity for anti-dsDNA and anti-Sm antibodies with clinical manifestations and serological indicators of SLE
Next, we examined the clinical significance of double positivity for anti-dsDNA and anti-Sm antibodies in SLE. Based on the status of anti-dsDNA and anti-Sm antibodies, patients with SLE were categorized into three groups: double negativity (negativity for anti-dsDNA and anti-Sm antibodies), single positivity (positivity for anti-dsDNA or anti-Sm antibodies), and double positivity (positivity for anti-dsDNA and anti-Sm antibodies).
Compared with the double-negative group, the single-positive group had a shorter disease duration, more common anti-U1RNP positivity, lower leukocyte and neutrophil counts, and higher ANA titers (Table 4). C3 and C4 levels were significantly lower in the single-positive group than in the double-negative group; however, the difference in SLEDAI 2000 and mSLEDAI 2000 scores between the two groups was not statistically significant (Figure 1).
Table 4.
The clinical manifestations and serological indicators of SLE with double positivity for anti-dsDNA and anti-Sm antibodies.
| Variable | Double negativity for both anti-dsDNA and anti-Sm antibodies | Single positivity for anti-dsDNA or anti-Sm antibodies | Double positivity for anti-dsDNA and anti-Sm antibodies | p | |||
|---|---|---|---|---|---|---|---|
| Value | N | Value | N | Value | N | ||
| Age (years) | 35 (28, 50) | 120 | 38 (28, 49) | 193 | 31 (26, 40)a,b | 95 | 0.006 |
| Disease duration (months) | 36 (5, 96) | 120 | 12 (1, 72) a | 193 | 6 (1, 30) a | 95 | <0.001 |
| Rash, n (%) | 35 (29.2) | 120 | 80 (41.5) | 193 | 61 (64.2)a,b | 95 | <0.001 |
| Arthritis, n (%) | 13 (10.8) | 120 | 36 (18.7) | 193 | 28 (29.5) a | 95 | 0.002 |
| Vasculitis, n (%) | 16 (13.3) | 120 | 31 (16.1) | 193 | 31 (32.6)a,b | 95 | 0.001 |
| Leukocyte count (109/L) | 5.5 (3.6. 7.1) | 120 | 4.1 (3.0, 6.4) a | 193 | 3.7 (3.0, 5.0) a | 95 | <0.001 |
| Neutrophil count (109/L) | 3.5 (2.3, 5.5) | 120 | 2.5 (1.8, 4.6) a | 193 | 2.5 (1.7, 3.5) a | 95 | <0.001 |
| Lymphopenia, n (%) | 34 (28.3) | 120 | 71 (36.8) | 193 | 43 (45.3) a | 95 | 0.037 |
| Hemoglobin (g/L) | 113 (94, 128) | 120 | 110 (93, 124) | 193 | 105 (90, 114) a | 95 | 0.031 |
| Antinuclear antibody titer | 320 (100, 3200) | 119 | 1000 (320, 3200) a | 193 | 1000 (320, 3200) a | 94 | <0.001 |
| Anti-U1RNP, n (%) | 23 (19.2) | 120 | 79 (40.9) a | 193 | 66 (70.2)a,b | 94 | <0.001 |
| Anti-ribosomal P protein, n (%) | 24 (20.0) | 120 | 40 (20.7) | 193 | 33 (35.1)a,b | 94 | 0.014 |
| Complement 3 (g/L) | 0.690 (0.490, 0.852) | 119 | 0.530 (0.380, 0.750) a | 193 | 0.429 (0.290, 0.612)a,b | 95 | <0.001 |
| Complement 4 (g/L) | 0.130 (0.068, 0.180) | 119 | 0.102 (0.065, 0.143) a | 193 | 0.067 (0.060, 0.105)a,b | 95 | <0.001 |
| SLEDAI 2000 scores | 11 (6, 17) | 119 | 12 (8, 19) | 192 | 17 (12, 22)a,b | 95 | <0.001 |
| Modified SLEDAI 2000 scores | 11 (6, 17) | 119 | 11 (7, 18) | 192 | 15 (10, 20)a,b | 95 | 0.001 |
Except where indicated otherwise, values are median (P25, P75).
Significantly different from patients with double negativity for anti-dsDNA and anti-Sm antibodies.
Significantly different from patients with single positivity for anti-dsDNA or anti-Sm antibodies.
RNP, ribonucleoprotein; SLE, systemic lupus erythematosus; SLEDAI 2000, Systemic Lupus Erythematosus Disease Activity Index 2000.
Figure 1.
Comparison of disease activity indicators of SLE among double-negative, single-positive, and double-positive groups. Double-negative group, negativity for anti-dsDNA and anti-Sm antibodies; single-positive group, positivity for anti-dsDNA or anti-Sm antibodies; and double-positive group, positivity for anti-dsDNA and anti-Sm antibodies.
SLE, systemic lupus erythematosus; SLEDAI 2000, Systemic Lupus Erythematosus Disease Activity Index 2000.
Patients in the double-positive group were younger and had a shorter disease duration than those in the double-negative group. Rash, arthritis, vasculitis, lymphopenia, anti-U1RNP positivity, and anti-ribosomal P protein positivity were more common in the double-positive group than in the double-negative group, and the double-positive group had lower leukocyte, neutrophil, and hemoglobin levels. Furthermore, the double-positive group had lower C3 and C4 levels and higher SLEDAI 2000 scores. After excluding the anti-dsDNA antibody scores, the mSLEDAI 2000 scores remained significantly different between the two groups.
In the comparison of the single- and double-positive groups, patients in the double-positive group were younger and more frequently had rashes, vasculitis, anti-U1RNP positivity, and anti-ribosomal P protein positivity. Concerning disease activity, the double-positive group showed lower C3 and C4 levels and higher SLEDAI 2000 and mSLEDAI 2000 scores.
Comparison of disease activity between the double-positive group and the anti-Sm-positive-only and anti-dsDNA-positive-only groups
As mentioned above, the mSLEDAI 2000 scores were significantly higher in patients with anti-Sm positivity than in those with anti-Sm negativity. By contrast, there was no significant difference between the mSLEDAI 2000 scores of patients with anti-dsDNA positivity and those with anti-dsDNA negativity. Therefore, although the mSLEDAI 2000 scores were significantly higher in the double-positive group than in the single-positive group, it still did not prove that the mSLEDAI 2000 scores differed between the double-positive and anti-Sm-positive-only groups. Therefore, we further assessed the differences in disease activity indicators between the two groups. The results showed that both SLEDAI 2000 and mSLEDAI 2000 scores were significantly higher in the double-positive group than in the anti-Sm-positive-only group, and C3 and C4 levels were significantly lower in the double-positive group than in the anti-Sm-positive-only group (Figure 2(a)). In addition, the comparison between the double-positive and anti-dsDNA-positive-only groups presented similar results (Figure 2(b)).
Figure 2.
Comparison of disease activity indicators of SLE between the double-positive group and the anti-Sm-positive-only group (a) and the anti-dsDNA-positive-only group (b).
SLE, systemic lupus erythematosus; SLEDAI 2000, Systemic Lupus Erythematosus Disease Activity Index 2000.
Changes in indicators of disease activity following changes in antibody status in patients with double positivity for anti-dsDNA and anti-Sm antibodies
In this cohort, complete follow-up data were available for 41 patients with double positivity for anti-dsDNA and anti-Sm antibodies who had a median follow-up time of 27 (11, 75) months, so we assessed changes in indicators of disease activity in these patients as their antibody status changed. Of these patients, 16 converted to single-positive, 8 to double-negative, 3 to single-positive and then to double-negative, and the remaining 14 were persistently double-positive. Regardless of whether the conversion was single-positive or double-negative, patients had significantly lower SLEDAI 2000 and mSLEDAI 2000 scores and significantly higher C3 levels. C4 levels were significantly elevated in patients with double-positive to double-negative conversions, and were close to being statistically different in patients with double-positive to single-positive conversions (p = 0.060; Figure 3(a)). Patients who remained double-positive showed no significant improvement in SLEDAI 2000 scores, although C3 and C4 levels were also significantly elevated (Figure 3(b)).
Figure 3.
Comparison of disease activity indicators of SLE in the antibody status changed group (a) and the antibody status unchanged group (b) in double-positive follow-up patients.
SLE, systemic lupus erythematosus; SLEDAI 2000, Systemic Lupus Erythematosus Disease Activity Index 2000.
Value of double positivity for anti-dsDNA and anti-Sm antibodies in recognizing severe disease activity in SLE
Since double positivity for anti-dsDNA and anti-Sm antibodies was associated with higher SLEDAI 2000 scores, double positivity for anti-dsDNA and anti-Sm antibodies may be valuable for identifying disease activity in SLE. Therefore, we evaluated the performance of different anti-dsDNA and anti-Sm antibodies in recognizing severe SLE disease activity. The statuses of the antibodies were categorized into four types: anti-dsDNA positivity, anti-Sm positivity, double positivity for anti-dsDNA and anti-Sm, and positivity for anti-dsDNA and/or anti-Sm. Based on SLEDAI 2000 scores, patients with SLE were classified as having mild-to-moderate or severe disease activity. In recognizing patients with severe disease activity, double positivity had the highest specificity and highest Youden index, although they showed the lowest sensitivity; moreover, the positive predictive value and positive likelihood ratio for double positivity were significantly higher than for the other types of antibody statuses, and accuracy, negative predictive value, and negative likelihood ratio were similar among groups (Table 5).
Table 5.
Overall performance of different antibody statuses in recognizing severe disease activity in SLE.
| Antibody status | Sensitivity (%), 95% CI | Specificity (%), 95% CI | Accuracy (%) 95% CI | Youden index (%) | PPV (%), 95% CI | NPV (%), 95% CI | +LR, 95% CI | −LR, 95% CI |
|---|---|---|---|---|---|---|---|---|
| Anti-dsDNA positivity | 67.0 (60.3, 73.2) | 48.7 (41.4, 56.0) | 58.4 (53.6, 63.2) | 15.7 | 59.5 (55.4, 63.5) | 56.7 (50.8, 62.5) | 1.305 (1.105, 1.543) | 0.678 (0.534, 0.862) |
| Anti-Sm positivity | 42.3 (35.6, 49.2) | 74.3 (67.5, 80.4) | 57.4 (52.6, 62.2) | 16.6 | 65.0 (58.2, 71.2) | 53.4 (49.8, 56.9) | 1.650 (1.238, 2.199) | 0.776 (0.673, 0.894) |
| Double positivity for anti-dsDNA and anti-Sm antibodies | 32.6 (26.3, 39.3) | 86.9 (81.3, 91.3) | 58.1 (53.3, 62.9) | 19.5 | 73.7 (64.9, 80.9) | 53.4 (50.7, 56.1) | 2.487 (1.646, 3.759) | 0.776 (0.697, 0.864) |
| Positivity for anti-dsDNA and/or anti-Sm antibodies | 76.7 (70.5, 82.2) | 36.1 (29.3, 43.4) | 57.6 (52.8, 62.5) | 12.8 | 57.5 (54.3, 60.6) | 58.0 (50.4, 65.2) | 1.201 (1.055, 1.368) | 0.644 (0.473, 0.875) |
−LR, negative likelihood ratio; +LR, positive likelihood ratio; NPV, negative predictive value; PPV, positive predictive value; SLE, systemic lupus erythematosus.
In clinical practice, high- and shock-dose glucocorticoid therapy often suggests that patients with SLE are in a state of severe disease activity; therefore, we also counted the use of high- and shock-dose glucocorticosteroids in patients with different antibody statuses. The results showed that a higher proportion (63.2%) of patients with double positivity were treated with high- and shock-dose glucocorticoids (56.8% of patients with anti-dsDNA positivity, 61.4% of patients with anti-Sm positivity, and 56.9% of patients with anti-dsDNA and/or anti-Sm positivity), but the difference was not statistically significant.
Discussion
In SLE, autoantibodies are not only a typical clinical feature but also participate in pathological progression; they are closely related to clinical manifestations, serologic indicators, and disease activity.21,22 Monitoring changes in autoantibodies can aid in adjusting treatment regimens and prevent disease recurrence.20 –22 This study focused on the clinical significance of double positivity for anti-dsDNA and anti-Sm antibodies in SLE and discovered that such patients tend to have more organ involvement and higher disease activity.
One study reported that patients with SLE had a 63% positivity rate for anti-dsDNA antibodies, which are associated with arthritis, leukopenia, kidney involvement, and low C3 levels. 23 Another study from Italy, including 393 patients with SLE, reported that anti-dsDNA antibodies were positively associated with lupus nephritis and anti-RNP antibodies and negatively associated with C4 levels and serositis, but not with the European Consensus Lupus Activity Measurement. 24 Gheita et al. reported that 61.4% of female patients with SLE were positive for anti-dsDNA antibodies, with significantly higher levels in patients with musculoskeletal manifestations and significantly lower levels in patients with neuropsychiatric manifestations. Patients with moderate disease activity tended to have higher anti-dsDNA antibody levels than those with mild disease activity or remission. However, the difference was not statistically significant. 25 Shang et al. reported that not only were serum anti-dsDNA levels significantly higher in patients with SLE with moderate–severe disease activity than in those with mild disease activity, but serum anti-dsDNA levels were positively correlated with SLEDAI 2000 scores. 9 In the present study, we discovered that anti-dsDNA positivity in SLE patients was 59.6%, which was positively correlated with alopecia, rash, arthritis, leukopenia, anemia, anti-Sm positivity, and anti-U1RNP positivity, and negatively correlated with neuropsychiatric lupus. Furthermore, patients with anti-dsDNA positivity tended to have higher disease activity, such as lower C3 and C4 levels and higher SLEDAI 2000 scores, although the difference in mSLEDAI 2000 scores between patients with anti-dsDNA positivity and anti-dsDNA negativity was not statistically significant. Therefore, despite the differences in the inclusion of populations, races, sample sizes, and antibody detection methods in the above studies, which led to slightly different results, all of them essentially revealed that anti-dsDNA antibodies were associated with disease activity in SLE.
The association between anti-Sm antibodies and the clinical manifestations of SLE has also been extensively investigated.26 –28 A study of Chinese patients with SLE reported that 469 (29.6%) patients were positive for anti-Sm antibodies, which was associated with arthritis, renal involvement, malar rash, vasculitis, and low serum C3. 26 The anti-Sm-positive group had significantly higher positivity for ANA titers, anti-dsDNA, anti-La/SSB, and anti-U1RNP antibodies than the anti-Sm-negative group, and the SLEDAI scores were higher in patients with anti-Sm positivity than in those with anti-Sm negativity. 26 In a large multiethnic cohort including 2322 patients with SLE, the positivity rate for anti-Sm antibodies was 24.9%; patients with anti-Sm antibodies were diagnosed with SLE at a younger age and had a shorter disease duration than those without anti-Sm antibodies. 27 Anti-Sm antibodies were positively associated with serositis, lupus nephritis, hemolytic anemia, leucopenia, lymphopenia, thrombocytopenia, vasculitis, Raynaud’s phenomenon, neurological disorders, psychosis, ANA titers, and anti-dsDNA antibodies. 27 In patients with new-onset SLE, baseline SLEDAI 2000 scores were comparable between patients with anti-Sm antibodies and patients without anti-Sm antibodies; however, anti-Sm positivity was associated with higher SLEDAI 2000 scores and anti-dsDNA titers at 12 months. 13 Our results generally agree with those described above, suggesting that anti-Sm antibodies are associated with disease activity in SLE and are not just the hallmark antibodies of SLE.
In contrast to studies targeting individual antibodies, only a few small-sample studies have investigated the clinical significance of double positivity for anti-dsDNA and anti-Sm antibodies in SLE. As early as 1979, Winn et al. compared the clinical characteristics of three groups of patients with anti-DNA positivity alone (n = 32), anti-Sm positivity alone (n = 61), and double positivity (n = 42) but did not find any unique clinical features in the double-positive group. 29 In 1983, Beaufils et al. studied 34 patients with SLE, including 12 with anti-DNA and anti-Sm antibodies and 22 with anti-DNA antibodies alone and discovered that patients in the double-antibody group had more cutaneous vasculitis, pulmonary involvement, and cardiovascular manifestations but less severe renal lesions. 30 Another study reported the clinical characteristics of eight patients with double positivity for anti-dsDNA and anti-Sm antibodies out of 51 patients with SLE. All patients were in the active phase of the disease, with the most common clinical manifestations being pulmonary, renal, and central nervous system involvement. However, the study did not compare the clinical characteristics of these patients with other patients. 14 Janwityanuchit et al. divided 119 patients with SLE with anti-Sm antibody positivity into 4 groups: 15 with anti-Sm positivity alone, 15 with double positivity for anti-Sm and anti-dsDNA antibodies, 46 with double positivity for anti-Sm and anti-RNP antibodies, and 43 with triple-positivity for anti-Sm, anti-dsDNA, and anti-RNP antibodies. 15 In patients with double positivity for anti-Sm and anti-dsDNA antibodies, dermatological and renal manifestations were more common, whereas vascular, cardiopulmonary, neurological, hematological, and arthropathic lesions were not more prevalent. 15 Therefore, the results of the above-mentioned studies are inconsistent.
In the present study, more patients with SLE were included, including 120 with double negativity, 193 with single positivity (positivity for anti-dsDNA or anti-Sm antibodies), and 95 with double positivity. The double-positive group showed more clinical manifestations, lower C3 and C4 levels, and higher SLEDAI 2000 and mSLEDAI 2000 scores compared to the double-negative and single-positive groups. In addition, the double-positive group had lower complement levels and higher SLEDAI 2000 and mSLEDAI 2000 scores than the anti-dsDNA-positive-only and anti-Sm-positive-only groups. Although there was no significant difference in the SLEDAI 2000 and mSLEDAI 2000 scores between the single-positive and double-negative groups, the single-positive group still had lower leukocyte, C3, and C4 levels, suggesting that the single-positive group may have had more severe disease activity than the double-negative group. Therefore, although anti-dsDNA and anti-Sm antibodies are separately associated with SLE disease activity, they have a synergistic effect, and the simultaneous presence of both antibodies tends to predict higher disease activity. During follow-up, disease activity was significantly reduced when the antibody status of double-positive patients changed to single-positive or double-negative, but the improvement in SLEDAI 2000 scores was not significant in patients with persistent double positivity, confirming that double positivity for anti-dsDNA and anti-Sm antibodies is associated with high disease activity in SLE.
In recognizing severe SLE disease activity, double positivity for anti-dsDNA and anti-Sm antibodies had the highest specificity, positive predictive value, positive likelihood ratio, and highest Youden index compared to the other three antibody statuses, albeit with the lowest sensitivity. In addition, the higher proportion of double-positive patients treated with high-dose and shock-dose glucocorticoids supports the high specificity of double positivity in recognizing severe disease activity. Therefore, double positivity for anti-dsDNA and anti-Sm antibodies can help identify severe SLE disease activity and is valuable in guiding the development of treatment regimens.
The shortcomings of the present study require attention. First, the study was retrospective, and data were inevitably missing. Second, the study did not consider the effect of treatment on antibody status, which could have biased the results; it also did not assess patients’ organ damage, treatment outcomes, etc., thus preventing further study of the effect of double positivity for anti-dsDNA and anti-Sm antibodies on the patients’ prognosis. Third, the study did not focus on the relationship between anti-dsDNA and anti-Sm titers and clinical manifestations and disease activity of SLE. Fourth, the study was a single-center study, so the findings need to be confirmed by more centers, especially from different countries and regions.
Conclusion
Our study suggests that patients with double positivity for anti-dsDNA and anti-Sm antibodies are a special group of SLE patients with more clinical manifestations and higher disease activity. Double positivity for anti-dsDNA and anti-Sm antibodies may help identify patients with severe disease activity who frequently require higher glucocorticoid doses.
Supplemental Material
Supplemental material, sj-docx-1-tab-10.1177_1759720X251379588 for Double positivity for anti-dsDNA and anti-Sm antibodies represents higher disease activity in systemic lupus erythematosus by Lin Zhang, Lei Zhang, Shanshan Chen, Zhichun Liu and Leixi Xue in Therapeutic Advances in Musculoskeletal Disease
Acknowledgments
We are very grateful to Dr. Yun Huang (Department of Endocrinology, The Second Affiliated Hospital of Soochow University) for her assistance with the statistical analyses.
Footnotes
ORCID iD: Leixi Xue 
https://orcid.org/0000-0001-8415-7088
Supplemental material: Supplemental material for this article is available online.
Contributor Information
Lin Zhang, Department of Rheumatology and Immunology, The Second Affiliated Hospital of Soochow University, Suzhou, China.
Lei Zhang, Department of Rheumatology and Immunology, The Second Affiliated Hospital of Soochow University, Suzhou, China.
Shanshan Chen, Department of Rheumatology and Immunology, The Second Affiliated Hospital of Soochow University, Suzhou, China.
Zhichun Liu, Department of Rheumatology and Immunology, The Second Affiliated Hospital of Soochow University, Sanxiang Road No. 1055, Suzhou, Jiangsu 215004, China.
Leixi Xue, Department of Rheumatology and Immunology, The Second Affiliated Hospital of Soochow University, Sanxiang Road No. 1055, Suzhou, Jiangsu 215004, China.
Declarations
Ethics approval and consent to participate: This study was conducted in accordance with the World Medical Association Declaration of Helsinki and was approved by the Human Ethics Review Committee of the Second Affiliated Hospital of Soochow University (Approval No. JD-HG-2024-033). Owing to its retrospective nature, the requirement for informed consent was waived by the Human Ethics Review Committee.
Consent for publication: Not applicable.
Author contributions: Lin Zhang: Formal analysis; Investigation; Methodology; Project administration.
Lei Zhang: Data curation; Formal analysis; Investigation.
Shanshan Chen: Data curation; Formal analysis; Writing – review & editing.
Zhichun Liu: Conceptualization; Supervision.
Leixi Xue: Conceptualization; Data curation; Formal analysis; Methodology; Project administration; Resources; Writing – review & editing.
Funding: The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Gusu Health Talent Plan of Suzhou (GSWS2022043, 2022194).
The authors declare that there is no conflict of interest.
Availability of data and materials: The datasets used and/or analyzed in this study are available from the corresponding author upon reasonable request.
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Supplementary Materials
Supplemental material, sj-docx-1-tab-10.1177_1759720X251379588 for Double positivity for anti-dsDNA and anti-Sm antibodies represents higher disease activity in systemic lupus erythematosus by Lin Zhang, Lei Zhang, Shanshan Chen, Zhichun Liu and Leixi Xue in Therapeutic Advances in Musculoskeletal Disease