Genetics of the complement system and rheumatic diseases.

The complement system, especially the early components of the classic pathway, are critically involved in immune complex processing. The deposition of clusters of complement component C3b on a target marks it for elimination, primarily through an interaction with complement receptors. Not surprisingly, total and partial deficiencies of certain complement components and C3b receptors are associated with rheumatic diseases, particularly systemic lupus erythematosus. This predisposition is explicable, based on the critical role complement plays in immune complex handling.