Complement fixation by the F(ab')2-fragment of pepsin-treated rabbit antibody.

  • 1 May 1971
    • journal article
    • Vol. 20  (5) , 649-58
Abstract
The F(ab′)2-fragments of rabbit anti-ovalbumin and anti-human serum albumin IgG fixed between 30 and 50 per cent of guinea-pig complement when they were aggregated with the appropriate antigen. The fixation took place at 37° but not at 4° and was completely inhibited by 0.005 M EDTA. The fixation was more efficient when preformed immune aggregates were used rather than allowing the aggregates to form in the fixation mixture. The loss in haemolytic activity was probably due to the fixation of one or more of the late components (C3 to C9) of guinea-pig complement since no significant fixation of the C1 and C2 components could be found. These results may help to explain previous conflicting reports on the ability of 5S antibody to fix complement. The results also suggest that rabbit antibody F(ab′)2 may fix complement by a pathway which utilizes only the components C3 to C9 thus bypassing the more usual pathway initiated by C1 activation.