<P> The C3bBb complex is stabilized by binding oligomers of factor P (Properdin). The stabilized C3 convertase, C3bBbP, then acts enzymatically to cleave much more C3, some of which becomes covalently attached to the same surface as C3b . This newly bound C3b recruits more B, D and P activity and greatly amplifies the complement activation . When complement is activated on a cell surface, the activation is limited by endogenous complement regulatory proteins, which include CD35, CD46, CD55 and CD59, depending on the cell . Pathogens, in general, don't have complement regulatory proteins (there are many exceptions, which reflect adaptation of microbial pathogens to vertebrate immune defenses). Thus, the alternative complement pathway is able to distinguish self from non-self on the basis of the surface expression of complement regulatory proteins . Host cells don't accumulate cell surface C3b (and the proteolytic fragment of C3b called iC3b) because this is prevented by the complement regulatory proteins, while foreign cells, pathogens and abnormal surfaces may be heavily decorated with C3b and iC3b . Accordingly, the alternative complement pathway is one element of innate immunity . </P> <P> Once the alternative C3 convertase enzyme is formed on a pathogen or cell surface, it may bind covalently another C3b, to form C3bBbC3bP, the C5 convertase . This enzyme then cleaves C5 to C5a, a potent anaphylatoxin, and C5b . The C5b then recruits and assembles C6, C7, C8 and multiple C9 molecules to assemble the membrane attack complex . This creates a hole or pore in the membrane that can kill or damage the pathogen or cell . </P> <P> The lectin pathway is homologous to the classical pathway, but with the opsonin, mannose - binding lectin (MBL), and ficolins, instead of C1q . This pathway is activated by binding of MBL to mannose residues on the pathogen surface, which activates the MBL - associated serine proteases, MASP - 1, and MASP - 2 (very similar to C1r and C1s, respectively), which can then split C4 into C4a and C4b and C2 into C2a and C2b . C4b and C2b then bind together to form the classical C3 - convertase, as in the classical pathway . Ficolins are homologous to MBL and function via MASP in a similar way . Several single - nucleotide polymorphisms have been described in M - ficolin in humans, with effect on ligand - binding ability and serum levels . Historically, the larger fragment of C2 was named C2a, but it is now referred to as C2b . In invertebrates without an adaptive immune system, ficolins are expanded and their binding specificities diversified to compensate for the lack of pathogen - specific recognition molecules . </P> <P> Immunology textbooks have used different naming assignments for the smaller and larger fragments of C2 as C2a and C2b . The preferred assignment appears to be that the smaller fragment be designated as C2a: as early as 1994, a well known textbook recommended that the larger fragment of C2 should be designated C2b . However, this was amplified in their 1999 4th edition, to say that: "It is also useful to be aware that the larger active fragment of C2 was originally designated C2a, and is still called that in some texts and research papers . Here, for consistency, we shall call all large fragments of complement b, so the larger fragment of C2 will be designated C2b . In the classical and lectin pathways the C3 convertase enzyme is formed from membrane - bound C4b with C2b ." </P>

What is an outcome of the complement cascade