Evaluation of a BP180-NC16a enzyme-linked immunosorbent assay in the initial diagnosis of bullous pemphigoid.

Background: Bullous pemphigoid (BP) is the most common subepidermal immunobullous disease, characterized by circulating IgG autoantibodies targeting BP180 and BP230 hemidesmosomal proteins. Several immunological studies have demonstrated that the membrane proximal noncollagenous domain NC16a of BP180 is the immunodominant region targeted by BP autoantibodies. Recently, a commercial BP180 NC16a-specific enzyme-linked immunosorbent assay (ELISA) has become available for detecting pathogenic anti-BP180 autoantibodies in BP sera. However, it remains unclear whether the diagnostic potential of the ELISA is equivalent to that of the 'gold-standard' diagnostic technique of immunofluorescence (IF).

Objectives: To examine the usefulness of a commercially available BP180-NC16a ELISA in the initial serodiagnosis of BP.

Methods: Sera from a large cohort of patients with BP (n = 102) and control subjects (age- and sex-matched normal volunteers, n = 60; pemphigus foliaceus, n = 18; pemphigus vulgaris, n = 16) were assayed by BP180-NC16a ELISA. All BP sera were obtained at presentation before initiation of systemic immunosuppressive therapy. The values of IgG antibody levels measured by ELISA were compared with those measured by indirect IF on salt-split skin. Results Receiver operating characteristic analysis was used to calculate the cut-off value for the ELISA in the diagnosis of BP which maximizes both sensitivity and specificity, and to estimate the diagnostic accuracy of the ELISA as represented by the area under the curve (AUC = 0.965). A cut-off value of 9 was associated with a sensitivity of 89% (91 of 102 BP sera showed a positive result) and a specificity of 98%. Fifty-eight of 60 normal controls and all the pemphigus sera showed a negative result. There was a correlation between the mean ELISA values and indirect IF titres (Spearman rank correlation 0.286; P = 0.004).

Conclusions: Our results suggest that the BP180-NC16a ELISA is a useful tool for the detection of pathogenic anti-BP180 IgG autoantibodies at the initial disease stage of BP. Because it is not only highly sensitive and specific, but is also easy to perform, is objective, and semiquantitative, the ELISA may provide valuable information for the accurate and reliable serodiagnosis of BP.