Assessment of skin basement membrane zone antibodies in the urine of patients with acquired subepidermal immunobullous diseases

Background In bullous pemphigoid (BP), cicatricial pemphigoid (CP) and line ar IgA disease (LAD), autoantibodies to the basement membrane zone (BMZ) ar e found in skin and mucosa, blood and blister fluid. Objectives To assess whether BMZ antibodies might also be detected in urine , Methods Urine and serum samples from 62 patients (32 with BP, 17 with CP an d 13 with LAD) were analysed for antibody isotypes and subclasses by indire ct immunofluorescence, and urine and serum samples from 40 patients (25 wit h BP, eight with CP and seven with LAD) were screened for target antigens u sing immunoblotting. Results Fourteen of 32 patients with BP had detectable levels of IgG BMZ au toantibodies in their urine, and all 32 had positive sera, Of these 14 BP p atients, 13 had epidermal-binding serum autoantibodies at a titre >1:160, a nd one had dermal-binding serum antibodies at a titre of 1:40, BMZ autoanti bodies were not detected in the urine of the CP or LAD patients, but the co rresponding sera were of low titre or negative, IgG subclasses (IgG1-4) wer e less frequently detected in urine than in serum. IgG4 was the predominant subgroup found (10 urine samples and all 14 sera), followed by IgG1 (two u rine samples and 12 sera); IgG2 was detected in a single urine sample and t hree sera, and IgG3 was not detected. Eight of 25 BP and one of eight CP ur ine samples were positive on immunoblotting, and bound BP230 and/or BP180 w ith IgA and/or IgG autoantibodies. IgA autoantibodies were not detected in the urine of the seven LAD patients, The corresponding sera were often more positive, with 21 of 25 BP, five of eight CP and six of seven LAD sera imm unoblotting the major BP antigens, Conclusions The detection of IgG autoantibodies from urine samples using in direct immunofluorescence correlated with a high titre of IgG autoantibodie s in the serum. IgG and IgA autoantibodies in the urine were detected by im munoblotting, although less frequently than in serum, The finding of BMZ an tibodies in the urine of many BP patients may have clinical relevance, and may have a restricted application in the diagnosis of immunobullous disease .