Complement factor B plays an imortant role in the alternative complement activation pathway by comple, Xenopus/Amphibian,ing with C3b to create the active C3 convertase. The alternative activation pathway was the first to evolve, thus the components involved are very similar in physological different species. The caiman complement factor B is similar to the mammalian counterpart and consists of a single polypeptide chain of appro, Xenopus/Amphibian,imately 90 kDa which upon activation is cleaved in a Ba fragment (60 kDa) and a Bb fragment (30 kDa). This antibody reacts with unactivated caiman complement factor B and the Bb fragment of activated factor B.