Complement receptors and B lymphocytes.

Most of the biological processes depend on cell-to-cell and protein-to-cell interactions, which take place through receptors present on the cell surface. Various physiological systems are linked by such interactions, as is the case for innate and adaptative immune response. There is increasing evidence that two of the main actors involved in host defense, namely, the proteins of the complement system (nonspecific response) and the B lymphocytes (specific response), are strongly connected through the complement receptors displayed on the B-cell surface. Many parameters account for the importance of these molecules: (1) their diversity in terms of binding specificity allows them to interact with different fragments resulting from complement activation and C3 component proteolysis; (2) the structures of their extra- and intracytoplasmic domains differ from one receptor to another, controlling their interactions with other nall surface molecules as well as pathogens and regulating cell signaling; (3) their expression on the majority of the cells involved in immune response, especially B lymphocytes, make them an essential link between specific and nonspecific immune responses. This review deals with these different aspects, taking into account the most recent data.