Complement fixation by Brazilian pemphigus foliaceus antibodies in vitro

In order to examine the presence of intercellular substance antibodies (ICS Ab) which will fix complement in vitro, in the sera of patients with Brazilian pemphigus foliaceus (BPF), 7 BPF sera were tested using immunofluorescence (IF) and complement IF (CIF). All 7 sera possessed IgG ICS Ab at titers varying from 1/320 to 1/2,560 (normal human skin as substrates). Using CIF, 2 out of 7 sera proved to have a capacity to fix complement (C3) in vitro at a titer of 1/40. Although the titer of complement-fixing ICS Ab detected by CIF was lower than IgG ICS Ab detected by IF, these results with the evidence of frequent C3 deposition in the lesional skin of BPF suggest the necessity of further studies on the role of complement system in BPF.