This project concerns molecular studies of the immune response with particular emphasis on: (1) origin of antibody specificity, i.e., nature of interactions between antibody and antigen, how antibody structure determines antigenic specificity; (2) activation of effector function, i.e., relative importance of aggregation and conformational change of antibody caused by binding antigen as necessary and/or sufficient condition for activation of complement cascade; (3) cell surface receptors for peptides released in complement cascade which have chemotactic or related properties such as C3a and C5a.