A MURINE TRANSGENIC MODEL OF HUMAN CLASS I MHC-MEDIATED PROGRAMMED CELL DEATH

Abstract

376 Human class I MHC molecules have recently been shown to mediate programmed cell death (PCD) signals via a Fas-independent pathway, suggesting that this pathway may, like Fas/Fas ligand, be useful for conferring immune privilege. The present study was conducted to develop a murine model for PCD mediated via human class I MHC molecules. Methods: B6 mice and B6 mice expressing both HLA B27 and human β2-microglobulin transgenes (Tg++ mice) were used. PCD was evaluated using viable cell recovery, ethidium bromide/acridine orange staining/fluorescent microscopy, and propidium iodide staining/FACS. Anti-human class I MHC mAbs used included W6/32 and 5H7(specific for an α3 domain monomorphic determinant). Results: Initial studies in mice expressing a single human class I MHC transgene did not demonstrate PCD induction, however, human class I MHC transgene expression was relatively low. Mice expressing HLA B27 and human β2 microglobulin transgenes, however, demonstrated higher human class I MHC expression and underwent PCD following treatment with 5H7 mAb. Splenocytes undergoing 5H7-induced PCD demonstrated classic features of PCD: cell shrinkage, cytoplasmic vacuolization, DNA condensation, and apoptotic body formation. Similar to the human studies of 5H7-induced PCD, studies in murine Tg++ cells demonstrated a greater sensitivity of B cells than T cells to PCD induction. The murine model was also similar to the human model in that class I MHC-mediated PCD induction was profoundly influenced by MHC receptor crosslinking and also dependent on the epitope specificity of the inducing anti-class I MHC mAb. Anti-CD3 mAb enhanced PCD induction by 5H7 mAb in both murine and human cells, however, IL-2 reversed 5H7-induced PCD only in murine cells. Conclusions: These studies indicate that 1) high level expression of human class I MHC in murine cells renders them susceptible to PCD induction via anti-human class I MHC mAb, 2) similar to human lymphoid cells, crosslinking and epitope specificity of the anti-class I MHC mAb markedly influence PCD induction, 3) anti-CD3 mAb enhances human class I MHC-mediated PCD in both human and murine cells, and 4) Tg++ mice provide a useful model for study of human class I MHC-mediated PCD.