Autoreactivity to BP180 Neoepitopes in Patients With Pemphigoid Gestationis

Abstract

This case series characterizes immune profiles of pregnant people with pemphigoid gestationis.

Pemphigoid gestationis (PG) is a rare autoimmune blistering disorder that occurs in people who are pregnant, characterized by itchy erythematous papules, plaques, and blisters, starting periumbilically and then spreading.¹ In 10% of affected pregnancies, passive transfer of maternal antibodies can lead to neonatal pemphigoid (NP). In around 90% of patients, PG is thought to be caused by immunoglobulin G (IgG) autoantibodies against the NC16A domain of collagen XVII.² The role and significance of autoantibodies, other than IgG against NC16A, remain elusive.

Methods

We characterized patients with PG seen in the Department of Dermatology, Medical Center – University of Freiburg, Germany, between 2010 and 2018, using standard diagnostic tests, including histopathology, direct and indirect immunofluorescence (DIF and IIF), and enzyme-linked immunosorbent assay (ELISA). Immunoblot (IB) analyses were used to characterize specific immune profiles (detailed eMethods are described in the Supplement). Patient material (tissue, serum) and clinical data (Table; eMethods in the Supplement) were recorded in accordance with the Declaration of Helsinki and Institutional Guidelines and review by the Human Ethics Committee University of Freiburg (reference No. 235/15). Patient consent was waived.

Table. Immunological Profile and Clinical Data of Pemphigoid Gestationis Patient Cohort.

Patient	Obstetric history (parity at first diagnosis)a	Onset, wk	Paras affected	Immunofluorescence		Enzyme-Linked Immunosorbent Assay			Immunoblot			IgE, kU/L	Clinical data
				DIF (BMZ)	ss-IIF (∩)	BP180		BP230, U/ml	BP180	LAD1	LABD97
						FL, U	NC16A, U/ml
1	MP (PII)	30	II	C3, C4, IgG1	IgG	9.2b	54b	2	−	−	−	12	Umbilical sign, vesicular plaques
2	MP (PIII)	14	III	C3, C4, IgG1	IgG	20.5b	108b	1	−	−	−	10.2	Umbilical sign, generalized annular plaques and blisters
3	PP (PI)	26	I, II	NA	IgG	17b	69b	0	+	+	+	76.1	Umbilical sign, vesicular pattern
4	MP (PII)	36	II	C3,C4, IgG1	−	0.5	37b	3	−	+	+	8.3	Acral vesicles and tense blisters on extremities
5	PP (PI)	28	I	NA	IgG	8.1b	55b	1	+	+	+	90.4	Umbilical sign, annular plaques, acral vesicles
6	MP (G VI/ PI)	32	I, III, V	NA	IgG	79.2b	8	1	−	+	+	18.4	Acral and single enoral blisters
7	PP (PI)	pp.	I	C3, C4, IgG1	IgG	67.8b	1	14	NA	NA	NA	3.9	Acral erythema, vesicles and pp. umbilical erythema
8	MP (PII)	28	I, II	C3, C4, IgG1	-	NA	48b	3	NA	NA	NA	39.9	Generalized annular, vesicular plaques
9	MP (PIII)	pp.	III	C3, C4, IgG1	NA	NA	35b	0	NA	NA	NA	72.4	Acral vesicles
10	PP (PI)	NA	I	C3, C4, IgG1	-	7.3b	56b	0	−	−	−	NA	Umbilical sign, vesicular plaques
11	PP (PI)	pp.	I	C3, C4, IgG1	−	13.7b	49b	21	+	+	+	50.9	Generalized and acral tense blisters

Abbreviatons: C3, complement 3; C4, complement 4; DIF (BMZ), direct immunofluorescence depositions on basement membrane zone; FL, anti-full-length BP180 IgG; MP, multipara; NA, not available; PP, primipara; pp., postpartum; ss-IIF, indirect immunofluorescence on salt-split skin; +, positive; −, negative; ∩ epidermal staining in split skin test. Normal levels for FL: <4.64U, for NC16A BP180: <9 U/mL, for BP230: <9U/mL, for IgE: <100 kU/L.

^a Parity at first diagnosis indicates the number of parity (ie, first, second, or third child).

^b Positive results.

Results

Among 11 patients with PG, aged 24 to 41 years, all described intense pruritus. A total of 6 out of 11 patients presented with periumbilical lesions; 5 had predominantly acral lesions. One patient had children born with mild NP, spontaneously resolving within 1 week. No other newborns were affected in the present study cohort, and pregnancies were uneventful with unremarkable intrauterine fetal development. All patients were treated with topical or oral steroids with improvement.

Testing with DIF revealed linear complement C3c, C4d (Figure, A), discrete to strong linear IgG, and markedly strong IgG1 depositions (Figure, B) along the basement membrane zone (BMZ) in all patients, but no IgG4, IgE, or IgA depositions (data not shown). Tissue eosinophilia was identified in 6 of 7 biopsies; blood eosinophilia in 2 cases. Testing with IIF on salt-split skin (ss-IIF) showed IgG epidermal staining in only 60% of available serum samples (6 of 10). Antibodies against the full-length BP180 form (FL BP180) were present in 88% (8 of 9). The commercially available and routinely performed BP180 NC16A ELISA test result was negative in 2 patients, both of whom had FL BP180 and BP230 autoantibodies. Immunoblot analyses showed IgG antibodies reacting against extracellular epitopes LAD1 and LABD97 in 63% of available serum samples (5 of 8), with additional reactivity against FL BP180 in 3 of 8 (Figure, C).

Figure. Immunological Analyses in the Present Study Cohort of Patients With Pemphigoid Gestationis.

Direct immunofluorescence results of 6 patients with linear C4d (A) and IgG1 (B) depositions along the basement membrane zone (BMZ). As positive controls, skin samples of patients with classical bullous pemphigoid were used. Arrows highlight the positive staining along the BMZ. C, Immunoblot results from the patients in our cohort. On the right side, a schematic diagram of the epitopes of BP180, as identified per immunoblot, is shown. NA indicates not applicable, NC, negative control; PC, positive control.

Discussion

The present study data indicate that patients with PG predominantly produce IgG1 autoantibodies against BP180 epitopes. While few reports have described IgG4 predominance,³ our findings are in accordance with multiple other reports of IgG1 predominance, emphasizing the importance of complement fixation in PG. It is possible that differences in measurement techniques or in acuity of biopsied lesions could be responsible for differences noted in prior studies. Although BP180 NC16A ELISA has a reported sensitivity of 86% to 97%² and is recommended for diagnostic testing,² the present study results highlight that antibodies against both FL BP180 and BP230 can also cause PG. Autoantibodies for FL BP180 were initially reported in patients with noninflammatory bullous pemphigoid (BP) typically associated with dipeptidyl peptidase 4 inhibitor therapy,⁴ which were not being used by any of the present study patients. Interestingly, characteristic periumbilical lesions were identified in only 55% of the study patients, who were also the most severely affected. Patients with no or lower levels of NC16A BP180 autoantibodies presented with predominantly acral vesicles, which could represent a different clinical variant of PG. Although the detection of C3c along the BMZ using DIF is the gold standard for diagnosing PG,⁵ C4d depositions along the BMZ also seem to be PG-specific.⁶ One notable limitation of this study is the lack of full-length minus NC16A BP180 enzyme-linked immunosorbent assay. An evaluation of larger cohorts, ideally based on an international registry, would be of major importance to correlate the clinical course to an autoimmune profile in patients with PG.

Supplement.

eMethods.