Protein-protein interactions underlying molecular recognition are studied, utilizing monoclonal antibodies (Mabs) specific for the protein hen egg white lysozyme (HEL), a protein which has long served as a prototype for investigating the specificity of immune recognition. The X-ray structures of HyHEL-5 Fab complexed with 2 single site-directed mutants of HEL have been solved and refined: R68K which reduces the affinity of the complex by a factor of over 10 to the 3rd power, and R45K, which reduces affinity by only 10-fold. These results represent the first time structures have been obtained for 3 antigens, differing at only a single critical residue, complexed to the same antibody, and will provide valuable insight about the role of Arginine side chains in protein-protein interactions. We are beginning to define fundamental principles that will allow prediction of function from structure, principles that are critical to such applications as antibody design and vaccine development. We are also approaching the problem of vaccine development by investigating immunogenicity and protective epitopes in Shigella flexnerii. In addition, experiments with specific-pathogen- free and conventional BALB/c mice have established that plasmacytoma- refractory SPF BALB/cAnPt mice have naive T cell responses as well as associated restricted B cell responses. These results suggest a significant influence of antigenic exposure, particularly viral antigens, on development of the specificity repertoire and plasmacytomagenesis.
