This project involves the pattern of expression of rabbit class II major histocompatibility complex antigens. Previous work from this laboratory demonstrated the existence of five genes encoding class II alpha chains in the rabbit. These have now been surveyed for mRNA expression in normal and pathological tissues of the rabbit. The results obtained are for the most part consistent with the tentative assignments of these genes as homologues of human alpha chain genes by strength of hybridization. The RLA genes referred to as RLA-DR alpha, RLA-DQ alpha and RLA-DP1 alpha are expressed with a pattern identical to that observed in the human for the HLA genes of the same name. Expression studies of RLA-DP2 alpha demonstrate a larger (3.6 kb) transcript, suggesting homology to the poorly understood human gene HLA-DZ alpha. This has now been borne out by sequence analysis. Northern blot analysis of RLA-DN alpha shows nothing resembling a mature class I alpha chain transcript but instead a very large transcript expressed most strongly in heart. This phenomenon is under study. A panel of class II-positive rabbit continuous cell lines has been established largely but not exclusively by in vitro viral transformation. Most of the viral transformants are macrophage-like in properties, but very recent experiments with human T lymphotropic virus I (HTLV-I) suggest that rabbit cells can be readily transformed by this virus.