Functional Characterization of an IgE-Class Monoclonal Antibody Specific for the Bullous Pemphigoid Autoantigen, BP180

Abstract

BP180 (collagen XVII) is the target antigen in several autoimmune diseases including bullous pemphigoid (BP). Both IgE and IgG class autoantibodies have been shown to be pathogenic in BP; however, studies designed to elucidate the patho-mechanisms mediated specifically by the IgE-class autoantibodies are limited by the low levels (ng/mL) of IgE in human sera. In this report, we developed mouse IgE class monoclonal antibodies (MAbs) against the immunodominant NC16A domain of the human BP180 protein and characterized two of the resultant MAbs, designated 395A5 and 395D2. Epitope mapping studies revealed that both MAbs target segment 2 of NC16A, as was described for IgE and IgG class BP autoantibodies. Also similar to BP IgE, MAb 395A5 showed indirect immunofluorescence labeling of the basement membrane zone (BMZ) of human skin, stimulated histamine release from mast cells when triggered with NC16A, and induced keratinocyte production of IL-8. The 395D2 MAb was also able to trigger antigen-specific histamine release from mast cells; however, in contrast to BP IgE and 395A5, 395D2 did not label the cutaneous BMZ, nor did it induce IL-8 production in keratinocytes. In summary, these studies underscore the importance of functionally characterizing MAbs generated for use in human disease models. The 395A5 IgE class murine MAb was shown to share several key functional properties with the pathogenically active IgE produced by BP patients. We therefore expect that this MAb will prove to be a useful tool for dissecting the mechanisms used by BP180-NC16A-specific IgE antibodies in the induction of BP skin lesions.

Biomarkers related to bullous pemphigoid activity and outcome

“…As for the IgG isotype, serum levels of anti‐BP180 NC16A IgE were correlated with disease activity and disappearance of these antibodies was associated with clinical remission . The pathogenicity of specific anti‐BP180 IgE has been proven by several in vitro experiments and by in vivo mouse models . Similarly, the therapeutic benefits brought by the selective suppression of the IgE activity by omalizumab, in BP patients resistant to corticotherapy, are also an argument for the IgE pathogenicity …”

IgE-mediated mechanisms in bullous pemphigoid and other autoimmune bullous diseases

“…[20,[115][116][117] The secretion from cultured keratinocytes was also seen in response to incubation with a monoclonal antihuman BP180 NC16A IgE. [114] Furthermore, incubation of keratinocytes with anti-BP180 IgE led to internalization of BP180. [118] Both effects have previously been shown for IgG-anti BP180 antibodies.…”

“…In the first approach, the effect of anti-BP180 IgE was investigated in vitro. Incubation of cultured human keratinocytes with IgE isolated from BP sera resulted in the release of IL-6 and IL-8, [113,114] two cytokines that may mediate disease development in BP, e.g. by the attraction of inflammatory cells.…”

Role of IgE in autoimmunity

“…13 A study of an SLE cohort that included patients from France and the United States revealed the presence of self-reactive IgE against at least 7 autoantigens, for which 65% of the subjects presented IgE autoantibodies to 1 or more of them (Table I). 4,5,[14][15][16][17][18][19][20][21][22][23][24][25][26] The prevalence was even greater within the subgroup of patients with active disease (83%). Levels of IgE specific for double-stranded DNA (dsDNA) showed the most significant association with disease activity and hypocomplementemia.…”