Comparative sensitivity of indirect immunofluorescence to immunoblot assay for the detection of circulating antibodies to bullous pemphigoid antigens 1 and 2

The sera of 263 patients with bullous pemphigoid (BP) were tested by indirect immunofluorescence (IIF) on salt-split skin (SSS) and immunoblot (IB) assay, in order to assess the diagnostic sensitivity of these techniques. Among the 263 sera tested, 198 sera (75%) contained antibasement membrane zone antibodies demonstrable by IIF reacting to the epidermal (98%) or both the dermal and epidermal sides (2%) of SSS. One hundred and eighty-two of the 263 sera (69%) reacted by IB with BP antigens (Ag), most commonly the BPAg1 (93 cases, 51%), and a complex of BPAg1 and the 180 kDa minor BP antigen (BPAg2) (47 cases, 26%). BPAg2 alone was found in 42 cases (23%). A good correlation was found between the detection of autoantibodies by IIF and labelling of BPAg1 and/or BPAg2 by IB assay, in which 152 of 198 sera with an epidermal pattern in IIF identified a BP antigen. IB analysis of the 65 sera negative by IIF yielded positive results in 30 cases (46%). Thirty-one percent (13 of 42) of sera recognizing by IB BPAg2, were negative by IIF, as compared with 12% (11 of 93) of those recognizing BPAg1 (P < 0.01). Comparing the sensitivity of the two tests, IIF (75%) was found to be more sensitive than IB (69%). Thirty-five of the 263 sera (13%) remained negative by both techniques. It can be concluded from this study that IIF on SSS appears to be a sensitive and reliable assay for screening BP; IB should be performed for the sera that are negative by IIF as it may reveal circulating antibodies, particularly to BPAg2.