Abstract
Background
Rheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by the dysregulation of multiple cytokines. In RA, Interleukin (IL)-4 levels fluctuate throughout disease progression, exerting a pathogenic role at onset and an anti-inflammatory role in later stages. Evidence suggests that IL-4 levels also differ between sexes and may be associated with disease severity. Thus, this study aimed to assess sex-based differences in IL-4 serum levels among patients with RA and determine whether these differences correlate with clinical parameters.
Methods
A total of 51 patients with RA (34 females and 17 males) and a control group of 24 sex- and age-matched individuals were included. IL-4 serum levels were quantified using a multiplex bead-based assay, and clinical parameters—including disease duration, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA), disease activity score (DAS28), and health assessment questionnaire disease index (HAQ-DI)—were analyzed using the Mann-Whitney U test and Spearman’s correlation coefficient. Non-parametric effect size was determined using the Hodges-Lehmann estimator of the median difference, and a multivariate linear regression analysis was performed to account for potential confounding variables.
Results
IL-4 levels were significantly lower in RA patients compared to controls (p < 0.0001), with male patients exhibiting higher IL-4 levels than female patients (p = 0.001). IL-4 levels were negatively correlated with RF (p = 0.037) and DAS28 (p = 0.005) in the overall population, with disease duration in female patients (p = 0.033), and with CRP (p = 0.046) and DAS28 (p = 0.024) specifically in male patients.
Conclusions
Higher IL-4 levels in males with RA may contribute to reduced inflammation, which is associated with lower disease activity. Conversely, lower concentrations of this cytokine in females may exacerbate disease progression. However, further studies are needed to confirm these findings.
Supplementary Information
The online version contains supplementary material available at 10.1186/s42358-025-00500-4.
Keywords: Interleukin-4, Rheumatoid arthritis, DAS28, C-reactive protein, ESR, ACPA
Background
Interleukin (IL)-4 is a glycoprotein composed of 153 amino acids with an approximate molecular weight of 17.49 kDa (UniProtKB: ID P05112), encoded by the IL4 gene located on chromosome 5 [1]. Physiologically, this cytokine plays a crucial role in the immune response against helminth infections [2]; however, it has gained prominence in allergic diseases such as asthma and allergic rhinitis [3, 4]. In recent years, its pathogenic implications have been identified in various rheumatological diseases, including systemic lupus erythematosus, ankylosing spondylitis, systemic sclerosis, osteoarthritis, and rheumatoid arthritis (RA) [5]. IL-4 is primarily expressed by type 2 helper T cells (TH2) and follicular helper T cells (TFH), and to a lesser extent by NKT cells, eosinophils, basophils, mast cells, and type 2 innate lymphoid cells [6, 7].
IL-4 signaling is essential for the differentiation and maintenance of TH2-type cell populations, which arise following the activation of naïve T cells through the combined action of IL-4, IL-5, IL-9, and IL-13 [6, 7]. Specifically, IL-4 signals through two types of receptors composed of distinct subunits. The type I receptor consists of an IL-4Rα chain and a common γC chain, whereas the type II receptor includes the same IL-4Rα chain paired with the IL-13Rα1 chain, which can be activated by both IL-4 and IL-13 [6, 7]. Upon receptor activation, the Janus Kinase 1/Signal Transducer and Activator of Transcription 6 (JAK1/STAT6) signaling pathway is triggered, leading to the transcription of the GATA3 gene and other cell-specific proteins that contribute to the TH2 immune response [6, 7].
In inflammatory diseases such as RA, IL-4 exerts diverse functions depending on the disease stage and the presence of other proinflammatory cytokines [8–11]. Through murine models of RA, it has been characterized that IL-4 plays an anti-inflammatory role in the synovium through macrophage regulation, promoting an anti-inflammatory phenotype [12, 13]. Furthermore, also in macrophages, IL-4 has been described to decrease the production of IL-1β, IL-6, IL-12, MIF, and TNF-α, as well as PGE2 [7, 9]. IL-4 also has an immunoregulatory effect on neutrophil and eosinophil function, having beneficial effects in RA [13, 14]. All these described mechanisms support the characterization of IL-4 as a primarily anti-inflammatory cytokine in established RA [15].
Although the immunomodulatory role of IL-4 may be beneficial in RA, disease progression is driven by an imbalance between TH1 and TH2 cell populations, with a predominance of proinflammatory activity [16]. In the early stages of RA, IL-4 and TH2 cells are upregulated in synovial tissue and fluid, as well as in the peripheral blood of affected individuals; however, their levels decrease significantly in established RA [10, 17, 18]. It has been suggested that high IL-4 levels in early RA contribute to inflammation and disease progression, although the exact mechanisms remain unknown.
RA is a chronic systemic autoimmune disease of unknown etiology, characterized by a multifactorial inflammatory process involving both cellular and humoral immune responses. The disease exhibits notable clinical differences between males and females, with a prevalence two- to threefold higher in women than in men [19]. Clinically, RA is characterized by soft synovial joint swelling, morning stiffness, and tenderness, which result from the destruction of articular cartilage and bone erosion. Additionally, systemic manifestations can affect the eyes, lungs, heart, kidneys, and other organs [19]. Hormonal factors and potential involvement of the X chromosome have been proposed as contributors to sex-based disparities in RA; however, these mechanisms remain incompletely understood [20]. It has been hypothesized that these or other factors may enhance the transcription of genes associated with RA pathophysiology, particularly those related to cytokine-cytokine receptor interactions and TH1 / TH2 cell differentiation, as suggested by previous studies [21].
Given the complex immunopathogenesis of RA and the observed sex-based clinical differences, further investigation into cytokines and their role in disease presentation is warranted. This study aimed to determine sex-based differences in serum IL-4 levels among patients with RA and to establish their relationship with clinical disease parameters.
Methods
Subjects and samples
A total of 51 patients with RA were included, of whom 34 were women (66.6%) and 17 were men (33.3%), with a mean age of 50 ± 14.33 years. Patients included in this study were classified according to the 2010 American College of Rheumatology/European Alliance of Associations for Rheumatology (ACR/EULAR) criteria and were recruited from the rheumatology service of the O.P.D. Hospital Civil de Guadalajara “Fray Antonio Alcalde” in Guadalajara, Jalisco, Mexico. The control group consisted of 24 age- and sex-matched individuals, of whom 20 were women (83.3%) and 4 were men (16.7%), with a mean age of 48 ± 14.19 years. Exclusion criteria for both groups included the presence of infections or other rheumatic or inflammatory diseases.
For the RA patient group, a clinical assessment was performed, which included disease activity evaluation using the Disease Activity Score 28 erythrocyte sedimentation rate (DAS28-ESR), and functional disability through the Spanish version of the Health Assessment Questionnaire-Disability Index (HAQ-DI). In addition, serum samples were obtained from the peripheral blood of RA patients and stored at -20 °C until further analysis. The following determinations were performed: serum levels of C-reactive protein (CRP) and rheumatoid factor (RF) using a turbidimetric assay (Biosystems, Spain); ESR using the Wintrobe method; and anti-citrullinated peptide antibodies (ACPA) through a second-generation ELISA (Axis-Shield Diagnostics, UK).
Cytokine quantification
Serum samples were obtained from peripheral blood of both study groups and stored at -20 °C until use. IL-4 levels were quantified using the Bio-Plex Pro Human Cytokine 27-plex Assay kit (#M500KCAF0Y, Bio-Rad). All samples were processed according to the manufacturer’s instructions. For this study, only IL-4 levels are reported, as it was the only cytokine that exhibited significant sex-based differences.
Statistical analysis
Statistical analyses were performed using GraphPad Prism version 8.0 (GraphPad Inc., San Diego, USA). Data distribution was assessed using the Shapiro-Wilk normality test. Variables with a normal distribution are presented as mean ± standard deviation (SD), whereas non-normally distributed variables are presented as median and interquartile range (25th–75th percentiles). Group comparisons were conducted using the Mann-Whitney U test. For each statistically significant comparison, the non-parametric effect size was estimated using the Hodges–Lehmann (HL) estimator of the median difference, presented as HL value and 95% confidence interval (CI). The corresponding HL values are provided in Supplementary Table 1. Correlations between continuous variables were analyzed using Spearman’s correlation test. A multivariate linear regression analysis was performed to assess the association between IL-4 levels and sex in RA patients, adjusting for potential confounding variables (CRP, treatment, presence of comorbidities, and disease progression). Statistical significance was defined as p < 0.05.
Results
Clinical characteristics of study subjects
A total of 51 patients diagnosed with RA were included, comprising 34 women (66.6%) and 17 men (33.3%), with a mean age of 50 ± 14.33 years and a median disease duration of 5.5 (3–11.75) years. The HAQ-DI index had a mean score of 0.74 ± 0.51, indicating mild disability. On average, clinical disease activity in RA patients was classified as moderate according to the DAS28-ESR score (3.8 ± 1.36). Based on disease activity levels, patients were distributed as follows: 25.49% in remission (n = 13), 9.80% with mild activity (n = 5), 43.13% with moderate activity (n = 22), and 21.56% with high activity (n = 11).
Additionally, the presence of RA-specific autoantibodies, RF and ACPA, was assessed. RF titers were 63 (46.08–83.31) IU/mL, with 55.81% of patients exhibiting high-positive titers. ACPA titers were 110.3 (30.33–500) U/mL, with high-positive values detected in 80.39% of patients. Acute-phase reactants were also evaluated, revealing elevated levels of both ESR [30 (20–41) mm/h] and CRP [7.10 (4.05–15.05) mg/L]. The clinical characteristics and treatment regimens of the study participants are summarized in Table 1.
Table 1.
Clinical and demographic characteristics of patients with RA
| Variable | n = 51 |
|---|---|
| Age (years)a | 50 ± 14.33 |
| Femaleb | 34/51 (66.6%) |
| Maleb | 17/51 (33.3%) |
| Years of evolutionc | 5.5 (3-11.75) |
| Clinical evaluation | |
| ESRc | 30 (20-41) |
| C-reactive protein (mg/dL)c | 7.10 (4.05-15.05) |
| Rheumatoid factor (IU/mL)c | 63 (46.08-83.31) |
| ACPA (U/mL)c | 110.3 (30.33-500) |
| HAQ-DIa | 0.74 ± 0.51 |
| DAS28-ESR scorea | 3.82 ± 1.36 |
| Disease Activity (DAS28-ESR)b | |
| Remission (< 2.6) | 13/51 (25.49%) |
| Mild activity (≥ 2.6 < 3.2) | 5/51 (9.80%) |
| Moderate activity (≥ 3.2 < 5.1) | 22/51 (43.13%) |
| High activity (≥ 5.1) | 11/51 (21.56%) |
| Rheumatoid factor statusb | 63 (46.08-83.31) |
| Negative (< 20 IU/mL) | 0/43 (0.0%) |
| Positive (≥ 20 < 60 IU/mL) | 19/43 (44.19%) |
| High positive (≥ 60 IU/mL) | 24/43 (55.81%) |
| ACPA statusb | 110.3 (30.33-500) |
| Negative (< 5 U/mL) | 7/51 (13.72%) |
| Positive (≥ 5 <15 U/mL) | 3/51 (5.88%) |
| High positive (≥ 15 U/mL) | 41/51 (80.39%) |
| Treatment | |
| NSAIDb | 21/51 (41.18%) |
| Glucocorticoidsb | 2/51 (3.92%) |
| Methotrexateb | 40/51 (78.43%) |
| Sulfasalazineb | 37/51 (72.55%) |
| Chloroquineb | 8/51 (15.69%) |
| Hydroxychloroquineb | 15/51 (29.41%) |
| Biologicsb § | 1/51 (1.96%) |
aData presented as mean ± standard deviation (SD). bData presented as percentage (n). cData presented as median (25th and 75th percentiles). § The biologic drug administered was Rituximab. Abbreviations: ACPA, anti-citrullinated peptide antibodies; DAS28, Disease Activity Score 28; ESR, erythrocyte sedimentation rate; HAQ-DI, Health Assessment Questionnaire Disease Index; NSAID, nonsteroidal anti-inflammatory drugs
Serum IL-4 levels in RA patients according to sex
Serum IL-4 levels were significantly lower in RA patients compared to control subjects [2.18 (0.96–4.19) vs. 4.71 (3.23–5.71) pg/mL; p < 0.0001]. When stratified by sex, female RA patients exhibited significantly lower IL-4 levels than their male counterparts [1.37 (0.85–2.84) vs. 4.40 (2.04–5.90) pg/mL; p = 0.001; Fig. 1]. To assess the association of serum IL-4 levels with the patients’ sex, a multivariate linear regression was performed. After adjusting for C-reactive protein levels, disease duration, treatment, and comorbidities, the association between sex and serum IL-4 levels remained statistically significant (β= -2.498; 95% CI [-4.400] – [-0.596]; p = 0.012). Despite accounting for the variables mentioned above, it remains possible that these observed differences may be affected by the regulation and interaction of additional cytokines, which could be modulated in a sex-dependent fashion.
Fig. 1.
Serum IL-4 levels in RA patients and control subjects, as well as in RA patients stratified by sex. Data are presented as median (p25-p75). Group comparisons were performed using the Mann-Whitney U test. Abbreviations: CS, control subjects; RA, overall rheumatoid arthritis patients; RA-F, female rheumatoid arthritis patients; RA-M, male rheumatoid arthritis patients
Relationship between serum IL-4 levels and clinical features of RA patients stratified by sex
Serum IL-4 levels in RA patients were analyzed for correlations with age, disease duration, HAQ-DI, ESR, CRP, ACPA, and RF, with patients stratified as follows: total cohort (n = 51), females (n = 34), and males (n = 17). In the overall RA group, a significant negative correlation was observed between IL-4 levels and RF (rs = -0.319; p = 0.037). No significant correlations were identified for the other clinical parameters in the total patient group.
Among female patients, IL-4 levels were significantly negatively correlated with disease duration (rs = -0.377; p = 0.033). In contrast, among male patients, a significant negative correlation was observed between IL-4 and CRP levels (rs = -0.592; p = 0.042). No other significant correlations with clinical parameters were identified in either female or male RA patients. The correlations of serum IL-4 levels and clinical parameters of RA patients are shown in Table 2; significant correlations are highlighted in bold.
Table 2.
Association of serum IL-4 levels with clinical parameters in RA patients
| Variable | RA IL-4 (pg/mL) |
RA-F IL-4 (pg/mL) |
RA-M IL-4 (pg/mL) |
|||
|---|---|---|---|---|---|---|
| r s | p | r s | p | r s | p | |
| Age (years) | 0.007 | 0.963 | -0.269 | 0.124 | 0.033 | 0.899 |
| Evolution (years) | -0.114 | 0.441 | -0.377 | 0.033 | 0.002 | 0.993 |
| HAQ-DI (score) | -0.157 | 0.292 | -0.123 | 0.488 | -0.297 | 0.325 |
| ESR (mm/h) | -0.205 | 0.150 | -0.089 | 0.616 | -0.383 | 0.129 |
| CRP (mg/L) | -0.095 | 0.533 | -0.087 | 0.629 | -0.592 | 0.042 |
| ACPA (IU/mL) | 0.013 | 0.929 | -0.139 | 0.433 | -0.253 | 0.327 |
| RF (IU/mL) | -0.319 | 0.037 | -0.203 | 0.250 | -0.594 | 0.092 |
Correlations were determined using Spearman’s correlation test (rs). Abbreviations: ACPA, anti-citrullinated protein antibodies; CRP, C-reactive protein; DAS28, Disease Activity Score 28; ESR, erythrocyte sedimentation rate; HAQ-DI, Health Assessment Questionnaire-Disease Index; RA-F, female rheumatoid arthritis patients; RA-M, male rheumatoid arthritis patients; RF, rheumatoid factor
Association between IL-4 serum levels and clinical activity in RA patients
A statistical analysis was conducted to assess the relationship between IL-4 serum levels and clinical disease activity in the overall RA cohort, as well as in patients stratified by sex.
When patients were stratified by clinical activity groups, regardless of sex, a trend toward lower IL-4 levels was observed as disease activity increased [remission: 4.40 (1.63–5.58) pg/mL; mild activity: 3.23 (2.08–3.89) pg/mL; moderate activity: 1.37 (0.85–2.64) pg/mL; high activity: 1.37 (0.96–2.84) pg/mL; Fig. 2a]. Compared to the control group (4.71 pg/mL), IL-4 levels were significantly lower in the moderate (p < 0.0001) and high (p < 0.001) activity groups. Additionally, IL-4 levels in the moderate activity group were significantly lower than in the remission group (p < 0.045), with a trend toward statistical significance between the high activity and remission groups (p = 0.060; Fig. 2a). Correlation analysis revealed a significant negative correlation between IL-4 serum levels and disease activity assessed by DAS28-ESR (rs = -0.386; p = 0.005; Fig. 2b).
Fig. 2.
Serum IL-4 levels and clinical activity in RA patients. (a) IL-4 levels in control subjects (CS) and RA patients stratified by clinical activity. (b) Correlation between IL–4 levels and DAS28-ESR in the overall RA cohort. (c) IL-4 levels in female control subjects (CS-F) and female RA patients (RA-F) stratified by clinical activity. (d) Correlation between IL–4 levels and DAS28-ESR in female RA patients. (e) IL-4 levels in male control subjects (CS-M) and male RA patients (RA-M) stratified by clinical activity. (f) Correlation between IL–4 levels and DAS28-ESR in male RA patients. Data are presented as median (25th–75th percentiles). Group comparisons were performed using the Mann-Whitney U test. Spearman’s correlation test was used for correlation analysis. Abbreviations: DAS28-ESR, Disease Activity Score 28-Erythrocyte Sedimentation Rate; RA, rheumatoid arthritis patients; rs, Spearman’s correlation coefficient; CS, control subjects
When stratified by sex, female RA patients exhibited significantly lower IL-4 serum levels than female control subjects, irrespective of their clinical activity group [CS-F: 4.72 (3.23–5.71) pg/mL vs. RA-F: 1.37 (0.85–2.84) pg/mL; p < 0.0001]. When further stratified by clinical activity, all female RA subgroups showed significantly reduced IL-4 levels compared to controls: remission, 2.43 (0.64–4.58) pg/mL (p < 0.014); mild activity, 3.08 (1.07–3.23) pg/mL (p = 0.037); moderate activity, 1.02 (0.82–1.87) pg/mL (p < 0.0001); and high activity, 1.37 (0.66–2.76) pg/mL (p < 0.001). However, no statistically significant differences were detected among the clinical activity groups within the female cohort (Fig. 2c). Correlation analysis revealed an inverse association between IL-4 levels and clinical activity in female patients, though this was not statistically significant (rs = -0.218, p = 0.214; Fig. 2d).
The same analytical approach was applied to male subjects. No significant differences in IL-4 levels were observed between male control subjects [CS-M: 4.74 (3.12–7.23) pg/mL] and male RA patients [4.40 (2.04–5.90) pg/mL; p = 0.477]. Similarly, no significant differences were detected among the clinical activity groups within the male cohort: remission, 5.26 (4.61–7.75) pg/mL; mild activity, 3.89 (3.23–4.54) pg/mL; moderate activity, 2.52 (1.19–5.95) pg/mL; and high activity, 2.90 (1.07–4.72) pg/mL. Due to insufficient sample sizes in the mild and high clinical activity groups, statistical tests could not be performed for these subgroups (Fig. 2e). In contrast to the female cohort, a statistically significant negative correlation was observed between IL-4 serum levels and clinical activity in male patients (rs = -0.543, p = 0.026; Fig. 2f).
Discussion
The potential involvement of IL-4 in the pathogenic mechanisms of autoimmune diseases has been previously reported. For instance, Girón-González et al. (2009) found significantly elevated IL-4 levels in primary Sjögren’s syndrome patients with monoclonal gammopathy, and a correlation between IL-4 levels and IgG concentrations was reported in this group [22]. Additionally, IL-4 has been implicated in diseases associated with the TH17 pathway, such as psoriasis. A recent study demonstrated that the administration of dupilumab, a monoclonal antibody targeting IL-4Rα, can inadvertently promote TH17 responses [23, 24].
In RA, IL-4 plays a crucial role in immunopathogenesis, particularly in pathways involving TH1 and TH2 differentiation [25], as well as in counteracting the effects of certain proinflammatory cytokines [8, 9]. Various findings suggest that IL-4 exhibits a dual role in RA pathophysiology, acting as a proinflammatory cytokine at disease onset and as a regulatory soluble factor in established RA, with a potential impact on clinical activity [9–11, 13]. Taken together, these observations suggest that IL-4 dysregulation contributes to inflammatory processes in autoimmune diseases through dual mechanisms: excessively low levels may activate alternative inflammatory pathways, while excessively high levels may promote allergic or autoimmune conditions.
The well-documented sex disparity in RA incidence and severity, with women exhibiting a higher prevalence and greater disease activity, has been attributed to hormonal influences and genetic factors linked to the X chromosome [20]. However, the potential role of cytokines in these sex-based differences remains an area of active investigation. In this study, we observed significantly lower serum IL-4 levels in RA patients compared to healthy controls, consistent with previous findings by Pavlovic et al. (2014), which support the notion that IL-4 is deregulated in RA [11]. Moreover, our findings revealed a more pronounced decrease in IL-4 levels among female RA patients compared to males. These results align with those reported by Pratap et al. (2020), who identified significant sex-based disparities in cytokine concentrations, including IL-4, IL-2, IL-17, IFN-γ, and IL-10 [26]. Additionally, Yu et al. (2020) analyzed transcriptomic data from synovial samples of RA patients and identified altered IL-4 mRNA expression compared to non-RA controls, with sex-based differences validated in an independent cohort showing significantly lower IL-4 mRNA and protein expression in synovial tissue from female patients [21]. Supporting the hypothesis of genetic influences on sex differences in RA, Suppiah et al. (2006) identified a higher frequency of genetic variants associated with reduced IL4 gene function in women with RA, making them less likely to be “high producers” of IL-4 [27].
Another interesting finding in the present study was the similar serum levels of IL-4 between the male RA patient group and the male control group. This finding could be related to the immunomodulatory role of androgens, which have been shown to have the ability to inhibit Th1 cell phenotype differentiation [28]. Furthermore, although there is no evidence to support that androgens directly induce a Th2 phenotype, there are reports suggesting that these hormones could influence the production of Th2-associated cytokines. For example, in a murine model of parasitic infection, Vargas-Villavicencio et al. (2006) observed a reduced production of Th2 cytokines, including IL-4 and IL-10, after a gonadectomy [29]. Thus, the similar levels of IL-4 observed in our study in both groups of males could reflect the immunomodulatory action of androgens.
Collectively, these results provide strong evidence that IL-4 mRNA and protein expression differ significantly between men and women with RA. These findings emphasize the importance of sex-dependent immune regulation and highlight the need for future research to elucidate the molecular and immunological mechanisms behind this expression pattern. In this context, exploring the IL-4/IL-13 axis, as well as polymorphisms in its shared receptor, could provide valuable information regarding its contribution to sex-specific regulation in RA.
In this study, a negative correlation was observed between IL-4 levels and RF titers in the overall RA cohort, suggesting a potential role for IL-4 in regulating RF production. Li et al. (2024) reported significant differences in serum IL-4 levels between seropositive and seronegative RA patients, highlighting its potential role in autoantibody production [30]. Also, Ad’hiah et al. (2018) reported that IL-4 mRNA expression was significantly lower in seropositive patients compared to seronegative ones (p = 0.001) [31]. In contrast, Baranov et al. (2024) found no statistically significant differences in IL-4 serum levels between patients with positive and negative RF (IgM). However, serum IL-4 concentrations were significantly higher among patients who were seronegative for ACPA compared to those who were seropositive [32]. These findings indicate that IL-4 may play a role in autoantibody production in AR. This highlights the dynamic roles of cytokines in RA and underscores the need for further research to define the relationship between IL-4 and RF, particularly in early disease stages or among patients with varying RF profiles.
When patients were stratified by sex, a negative correlation between IL-4 levels and disease duration was observed in female RA patients. This finding may be related to the distinct kinetics of IL-4 in different phases of RA [10]. These findings suggest that IL-4 levels increase during the early stages of RA but undergo significant changes as the disease progresses, with more pronounced alterations in female patients. Further research is needed to fully elucidate the role of IL-4 in RA pathogenesis and to determine the extent to which sex-based differences influence disease progression.
Regarding clinical activity, we observed a significant negative correlation between IL-4 levels and DAS28 scores in the overall RA cohort. However, when stratified by sex, this relationship was only maintained in male patients. These findings differ from those reported by Pavlovic et al. (2014), who did not find a statistically significant association between IL-4 levels and DAS28 or other clinical parameters such as age, CRP, ESR, and ACPA. This discrepancy may be attributed to differences in study design [11]. In this study, a strong negative correlation between IL-4 and C-reactive protein levels was observed exclusively in men. Although no sex-specific differences in IL-4-mediated regulation of the CRP production have been described, there is evidence that this cytokine can modulate the synthesis of acute-phase reactants. In an in vitro model of primary human hepatocyte culture, these cells were observed to decrease their CRP production in the presence of IL-4, reinforcing the anti-inflammatory role of this cytokine [33]. Additionally, there is evidence that supports that IL-4 decreases the production of inflammatory cytokines such as IL-6, one of the main inducers of CRP production [9]. The observation in this study that the male RA group exhibited higher IL-4 levels suggests that this cytokine may exert biological effects in CRP production. These findings also highlight the need for further studies to evaluate sex-dependent differences in IL-4 function over acute-phase reactant production.
This study has certain limitations, including a relatively small sample size, which may have reduced the statistical power of the stratified analyses, particularly in the male cohort. Therefore, future studies with larger sample sizes and appropriate statistical adjustments for potential confounders are necessary. Moreover, longitudinal studies could provide further insights into whether IL-4 levels fluctuate with disease activity or treatment response over time and whether these variations are sex-dependent in RA patients.
Conclusion
In conclusion, our findings support the existence of sex-specific differences in serum IL-4 levels among RA patients, highlighting a sex-dependent association between IL-4 levels and clinical disease activity. Additionally, our results suggest that IL-4 downregulation may be more pronounced in female RA patients as the disease progresses. However, future longitudinal research involving RA patients, stratified by gender, is required to understand the underlying mechanisms behind the dynamics of IL-4 in relation to clinical variables such as disease progression and treatment.
Supplementary Information
Below is the link to the electronic supplementary material.
Acknowledgements
We extend our gratitude to the Rheumatology Service of O.P.D. Hospital Civil “Fray Antonio Alcalde” for their invaluable support in patient recruitment. We also thank the Centro Universitario de Ciencias de la Salud (CUCS) for providing the necessary funding for the project from which this publication was derived.
Abbreviations
- ACPA
Anti-Citrullinated Peptides Antibodies
- ACR
American College of Rheumatology
- CRP
C Reactive Protein
- CS
Control Subjects
- DAS28
Disease Activity Score 28
- ESR
Erythrocyte Sedimentation Rate
- EULAR
European Alliance of Associations for Rheumatology
- GATA3
GATA Binding Protein 3
- HAQ-DI
Health Assessment Questionnaire-Disability Index
- IL-4
Interleukin-4
- JAK1
Janus Kinase 1
- MMP
Matrix Metalloproteinase
- NSAID
Nonsteroidal anti-inflammatory drug
- RA
Rheumatoid Arthritis
- RF
Rheumatoid Factor
- SD
Standard Deviation
- STAT6
Signal Transducer and Activator of Transcription 6
- TFH
T helper follicular cell
- TH1
T helper cell type 1
- TH2
T helper cell type 2
- TH17
T helper cell type 17
Author contributions
EJAD, data curation, interpretation of data, writing-original draft; JJRH, data curation, interpretation of data; GASZ, methodology, data acquisition; SGA, methodology, validation, interpretation of data; EEPG, data curation, formal analysis; VMLL, methodology, data acquisition, interpretation of data; SCC, methodology, data acquisition, validation; JFMV, conceptualization, funding acquisition, project administration; CJBH, conceptualization, writing-review and editing; IVRF; conceptualization, funding acquisition, project administration, writing-review and editing. All authors read and approved the final manuscript.
Funding
This research was funded by the Universidad de Guadalajara and the Centro Universitario de Ciencias de la Salud through the proSNI program and the PIN-2020-I fund, respectively, granted to Ilce Valeria Román Fernández.
Data availability
The datasets generated and/or analyzed during this study are not publicly available but can be obtained from the corresponding author upon reasonable request.
Declarations
Ethics approval and consent to participate
Written informed consent was obtained from all study participants, and all procedures were conducted in accordance with the ethical guidelines outlined in the Declaration of Helsinki. This study was approved by the Ethics, Research and Biosafety Committees of the Centro Universitario de Ciencias de la Salud of Universidad de Guadalajara under the approval number CI-04920.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The datasets generated and/or analyzed during this study are not publicly available but can be obtained from the corresponding author upon reasonable request.