Potential involvement of C-3 complement factor in amphibian fertilization

We have assessed the potential involvement of C-3, the third complement fac tor, and its receptor in Bufo arenarum fertilization. We show that a polycl onal antibody against a B. arenarum C-3-like factor (C3Ba) reacts specifica lly with components of the extracellular matrix (ECM) of coelomic eggs and the cell membrane of uterine eggs. Interestingly, we have identified a 163 kD protein immunoreactive with a monoclonal antibody against the CD11b alph a chain of the human C-3 receptor on the cell membrane of the animal pole o f uterine eggs, the site of entry of the sperm, but not in coelomic eggs (C R3Ba). Treatment of coelomic eggs with a pars recta oviductal-like protease , trypsin, induced the translocation of C3Ba from the ECM to the cell membr ane. Furthermore, inhibition of CR3Ba by trypan blue, as well as inhibition of C3Ba by anti-C3Ba on uterine eggs impaired fertilization, whereas ident ical treatment on sperm cells did not alter percentage fertilization. Our r esults suggest, (A) that changes in the localization of C3Ba from the ECM t o the cell membrane may be triggered by trypsin-like proteases during passa ge of eggs through the oviduct; and (B) that C3Ba/CR3Ba may be involved in B. arenarum fertilization. (C) 2000 Elsevier Science Inc. All rights reserv ed.