[Linear IgA bullous dermatosis in children with autoantibodies against 180 kDa pemphigoid antigen]

Humoral Epitope Spreading in Autoimmune Bullous Diseases

Autoimmune blistering diseases are characterized by autoantibodies against structural adhesion proteins of the skin and mucous membranes. Extensive characterization of their autoantibody targets has improved understanding of pathogenesis and laid the basis for the study of antigens/epitopes diversification, a process termed epitope spreading (ES). In this review, we have reported and discussed ES phenomena in autoimmune bullous diseases and underlined their functional role in disease pathogenesis. A functional ES has been proposed: (1) in bullous pemphigoid patients and correlates with the initial phase of the disease, (2) in pemphigus vulgaris patients with mucosal involvement during the clinical transition to a mucocutaneous form, (3) in endemic pemphigus foliaceus, underlining its role in disease pathogenesis, and (4) in numerous cases of disease transition associated with an intermolecular diversification of immune response. All these findings could give useful information to better understand autoimmune disease pathogenesis and to design antigen/epitope specific therapeutic approaches.

IgG, IgA and IgE autoantibodies against the ectodomain of BP180 in patients with bullous and cicatricial pemphigoid and linear IgA bullous dermatosis

BACKGROUND

Bullous pemphigoid (BP), linear IgA bullous dermatosis (LABD) and cicatricial pemphigoid (CP) are clinically distinct autoimmune bullous skin diseases characterized by autoantibodies against components of the epidermal basement membrane. Like most patients with BP, a significant subgroup of patients with CP has circulating IgG specific for BP180, a transmembraneous protein of hemidesmosomes. Moreover, sera of patients with LABD contain IgA autoantibodies reactive with a 97/120-kDa protein, LABD antigen 1, which is highly homologous to the extracellular portion of BP180.

OBJECTIVES

We aimed to determine whether, in these diseases, autoantibody reactivity to BP180 is restricted to distinct immunoglobulin subtypes.

METHODS

Utilizing a baculovirus-encoded form of the ectodomain of BP180, sera from patients with BP (n = 10), CP (n = 9), LABD (n = 10) and normal human control sera (n = 10) were analysed by immunoblot for IgG, IgA and IgE reactivity against BP180.

RESULTS

All of 10 BP sera displayed IgG, IgA and IgE reactivity with BP180. Six and seven of nine CP sera, respectively, contained IgG and IgA autoantibodies reactive with BP180, but none of nine sera contained BP180-specific IgE. Nine of 10 LABD sera contained IgA, and six of 10 IgG, which was reactive with BP180, but none of 10 sera showed IgE reactivity to BP180.

CONCLUSIONS

The presence of IgG and IgA autoantibody responses to BP180 in patients with three clinically distinct autoimmune bullous diseases indicates that an autoimmune response to the same distinct adhesion protein may lead to different clinical manifestations. It is therefore conceivable that variable epitopes of BP180 are targeted by the different autoantibody isotypes, resulting in the distinct clinical pictures.

Childhood bullous pemphigoid associated with IgA antibodies against BP180 or BP230 antigens

Linear IgA bullous dermatosis (LABD) comprises a heterogeneous group of subepidermal blistering disorders characterized by in situ bound IgA antibodies in epidermal basement membrane. We report three children presenting clinical and immunopathological features characteristic of LABD. By immunoblotting, the three patients' sera contained IgA antibodies that reacted against the bullous pemphigoid (BP) antigen 180 and or BP230, molecular markers for BP. In addition, IgG antibodies directed against the ectodomain of BP180 were detected by an enzyme-linked immunosorbent assay using a eukaryotic recombinant form of BP180. Consistent with recent studies suggesting that the LABD antigen 1, the predominant autoantigen of LABD, is either a proteolytic product of BP180 or an isoform of the BP180 gene, our findings indicate that a subset of children with features of LABD have a distinct form of BP associated with an IgA response.

Linear IgA bullous dermatosis with IgA antibodies exclusively directed against the 180- or 230-kDa epidermal antigens

This study describes the presence in sera from patients with linear IgA bullous dermatosis (LABD) of IgA antibodies specific for 230- or 180-kDa epidermal antigens. Of 11 patients' sera with IgA antibodies reactive with the epidermal antigens obtained from cultured keratinocytes, 6 sera recognized the 230-kDa antigen and co-migrated with the polypeptide recognized by a human monoclonal antibody against the 230-kDa bullous pemphigoid antigen (BPAgl). Five sera recognized the 180-kDa antigen and co-migrated with the polypeptide stained by a polyclonal antibody to the 180-kDa bullous pemphigoid antigen (BPAg2). None of these LABD sera contained IgG antibodies reactive with the basement membrane zone antigens and none labeled a 97-kDa epidermal antigen or a 290-kDa dermal antigen. Immunoaffinity-purified IgA antibodies from the 230 kDa band further reacted with the epidermal side of the skin basement membrane zone. Epitope mapping with rBP55, a fusion protein containing the C-terminal end of BPAg1, suggested that the major antigenic epitopes for LABD and BP antibodies on the 230-kDa antigen are different. Only one serum with IgA antibodies was found to label rBP55, contrasting with nine of ten BP sera reacting with this protein. Our study demonstrates the presence of an exclusive IgA response against the 230- or 180-kDa antigens in a subset of patients with LABD.