Antigen-specific T-cell hyporesponsiveness in MRL congenic mice can be explained by two independent cellular defects

MRL-+, MRL-lpr and B6-lpr have been shown to be useful models in studying systemic lupus erythematosus. MRL-lpr and B6-lpr differ from their congenic counterparts by the presence and expression of the homozygous recessive lymphoproliferation (lpr) gene. One manifestation of this gene is a massive T-cell proliferation that results in a generalized lymphadenopathy in older animals. A paradox that has developed out of the work utilizing the congenic mice is that the gene responsible for lymphoproliferation also appears to be responsible for the inability of T cells to respond to proliferative signals in vitro. In this paper we investigate the basis for this hyporesponsiveness in antigen-induced activation of proliferation and antibody synthesis. We have demonstrated that spleen cells from both MRL-+ and MRL-lpr mice gave minimal stimulation in a one-way mixed lymphocyte reaction against allogeneic T cells. These findings were extended to include antigen-specific proliferation involving antigen that must be processed and presented to responder lymphocytes in a H-2 restricted manner. Thus, MRL-+ and MRL-lpr spleen cells pulsed with ferredoxin also failed to stimulate ferredoxin-primed T cells from B10.Br animals in vitro. We then investigated whether any T-cell defect(s) was also contributing to this proliferative hyporesponsiveness. T lymphocytes from the spleen of MRL-+, 2-month-old MRL-lpr, and 6-month-old MRL-lpr were tested in a one-way mixed lymphocyte reaction. It was found that only the MRL-+ T cells gave responses approaching normal, suggesting lpr gene involvement in T-cell non-responsiveness. This was confirmed by the demonstration of an age-onset T-cell proliferative hyporesponsiveness in B6-lpr mice. This lpr gene-linked non-responsiveness was also shown to extend to T-cell helper function in a positive allogeneic effect assay. We can conclude from these studies that antigenic nonresponsiveness in MRL congenic mice can be explained by two defects: the failure of antigen-presenting cells in MRL-+ and MRL-lpr mice to provide the necessary signal(s) to immunocompetent T cells, this defect not being associated with the lpr gene, and the lpr gene controlled outgrowth of a unique T-cell population that cannot respond in our assay systems.