Unique surface phenotype of T cells in lymphoproliferative autoimmune MRL/Mp-lpr/lpr mice

MRL/l mice, which carry the mutant gene lpr, develop massive T cell lymphoproliferation and an autoimmune syndrome. The surface antigen profile of MRL/l lymphocytes was analyzed with rat monoclonal antibodies. They included YE1/9.9, anti-transferrin receptor; YE1/7.1, which reacts with a population of proliferating immature T cells; and YE1/19.1, a newly identified antibody reactive with a surface antigen on EL-4 cells, which consists of two disulfide-bonded polypeptide chains, each of 115,000 m.w. Flow cytometric analysis of lymphocytes from the enlarged lymph nodes of MRL/1 mice showed the majority of them to be Lyt-1+, YE1/7.1+, YE1/19.1+, YE1/9.9-. In contrast, YE1/7.1 and YE1/19.1 antibodies did not significantly react with lymphocytes from the congenic MRL/n mice, which lack the lpr gene and do not develop lymphoproliferation. Lymphocytes from younger MRL/l mice, which have almost normal size lymph nodes, were also YE1/7.1-, YE1/19.1-. A small proportion of mitogen-stimulated MRL/n lymph node cells appeared to express these antigens at low densities, but it is not known whether they represent a unique cell population. Among the several lymphoid cell lines tested, only the T lymphoma line EL-4 had the Lyt-1+, YE1/7.1+, YE1/19.1+ phenotype. These results suggest that the lpr mutation induces the expansion of a unique T cell subset.