Application of molecular cloning to studies on the complement system.

The isolation of cDNA and, in certain cases, genomic clones has been reported for the following complement proteins: C1q, C2, C3, C4, C5, C9, and factor B, C4b-binding protein and C1-inhibitor. The availability of cloned DNA has allowed rapid advances to be made in the understanding of the structure (from the derived amino acid sequences), function, biosynthesis and genetics of these proteins. This is most strongly illustrated from recent studies on the C2, factor B and C4 genes, which code for the class III molecules of the major histocompatibility complex, especially as certain allelic forms of these genes may be associated with disease susceptibility.