IMMUNOLOGY

Detailed explanation-1: -The formation of C3 convertases is the point at which the three pathways of complement activation converge, because both the classical pathway and MB-lectin pathway convertases C4b, 2b, and the alternative pathway convertase C3b, Bb have the same activity, and they initiate the same subsequent events.

Detailed explanation-2: -C3 Convertase This is the most important step in the complement cascade and occurs in the classic, alternative, and MBL pathways. C3b is a highly unstable molecule that has a unique thioester that allows covalent binding to a microbial cell.

Detailed explanation-3: -Factor B (Bf) is a component of the alternative pathway, which is activated by a diverse set of substances including components of yeast and bacterial cell walls and is usually antibody-independent.

Detailed explanation-4: -Key complement components C3b, iC3b, and C4b (see Ch. 19 for nomenclature) are generated as by-products of the classical pathway of complement activation.