β2-GPI mediates inactivation of intact C3. (A) β2-GPI enabled degradation of C3 by factor I and factor H (lanes 4-6), but C3 was not cleaved by factor I in the presence of factor H (lane 2). The mobility of C3 cleavage products of 43 and 41 kDa is indicated. No cleavage product at 68 kDa was detected. (B) Probes from experiment shown in panel A were immunostained using a monoclonal C3a antibody. Cleavage product of 77 kDa, which represents the α-chain fragment including the C3a domain, is indicated. (C) Fragment β2-GPI/I-IV (lanes 8-10) mediated lower cleavage activities of C3 than β2-GPI and β2-GPI/IV-V (lanes 11-14) showed no effect. (D) C3a staining of the probes demonstrated a C3a containing cleavage product of 77 kDa in the presence of β2-GPI (lane 1) and β2-GPI/I-IV (lanes 3-5). Representative Western blots of 4 experiments are shown.
