The Skn alloantigens of the mouse, expressed only by cells of the skin (and possibly the nervous system) is one of the instances of a true tissue- specific histoincompatibility. They were recognized by the invariable and prompt rejection of A and (B6xA)F1 donor skin grafts by lethally irradiated B6 mice reconstituted with (B6xA)F1 bone marrow or spleen cells [(B6xA/B6 chimeras], and serologically with Skn specific antiserum and monoclonal antibodies which react exclusively with epidermal cells of A mice. The primary objective of this proposal is to develop molecular genetic probes for the biochemical and molecular characterization of the Skn histocompatibility systems. A molecular approach will facilitate studies designed to determine the expression and function of these skin-selective alloantigens. With the development of Skn-specific monoclonal antibodies, and the isolation of a possible Skn polypeptide, during the previous funding period, the study of the Skn histocompatibility systems using molecular technology is now possible. The first two aims are proposed to address this important objective. The first aim is to purify, characterize and sequence Skn alloantigen(s). We have identified a protein of approximately 94 kDa from A epidermal lysates which will be initially characterized and sequenced. Using this information oligonucleotide probes will be constructed for eventual screening of epidermal cDNA libraries. The second aim is to develop and screen A strain epidermal cDNA libraries with a view to clone and sequence gene(s) encoding Skn antigen(s). Skn specific monoclonal antibodies already developed, and other being developed, will be used to screen this expression library. Using these antibodies and recombinant inbred strains, as well as the backcross segregants, further mapping of the Skn genes and definition of the Skn alloantigens in immunogenetic terms are proposed as Aim 3. With the monoclonal antibodies distinguishing allotypes of both Skn loci, it is now feasible to derive Skn congenic strains simply by serotyping, which will permit further immunogenetic analysis of Skn without resort to radiation chimeras and the uncertainties of varied genetic backgrounds (Aim 4). If successful in cloning a gene or genes for Skn, transgenic mice will be developed. Finally, an important question concerning natural self tolerance and acquired immunity is addressed in Aim 5 which is to determine if the pathologic changes in the skin induced in (B6xA)F1 mice receiving spleen cells from (B6xA)/B6 chimeras immunized against A strain Skn alloantigens are truly Skn specific. If the reaction is shown to be Skn- directed, then the Skn systems could potentially be of considerable clinical significance.