Murine mu chains obtained from the cell surface or secreted IgM of BCL1 tumor cells will be compared to understand the mechanism of attachment to IgM to the cell surface. Extra peptide peaks of radioactivity from cell surface IgM will be isolated and subjected to amino acid sequencing. The role of cell surface IgM and IqD in signaling for activation to replication and differentiation or to induction of tolerance will be further investigated. In particular, the relation of these signals to those induced by helper T cells will be analyzed. One approach will be to use T cell signals and anti-Igs in in vitro model systems, under conditions in which anti-Igs either block or stimulate replication of the relevant B cells. In addition, cell populations can be purified on the florescent activated cell sorter in order to obtain B cells which bear or lack particular cell surface isotypes. These maneuvers should allow the analysis of signaling in various B cell subsets. Transformation of B cells by Abelson virus will be studied in order to determine susceptible subsets, alteration of surface markers, to transform cells to build a library of cell lines representing different stages of differentiation, and to study differentiation in neoplastic B cells. Ia antigens on T cells from selected peritoneal exudate lymphocytes of immune guinea pigs will be studied biochemically in order to determine their relationship to B cell and macrophage Ia antigens. T cell recognition of virus infected cells will be analyzed with regard to the role of carbohydrate moieties of H-2D and H-2K and to viral glycoproteins. Comparative studies of cell surface gene products of chromosome 17 will be performed. Comparative peptide mapping of thymus leukemia antigen and QA antigen will be performed with H-2D and H-2K to determine structural homology among these proteins. This will permit isolation of common peptides among such gene products for amino acid sequencing.