Comparison of the capacity of murine and human class I MHC molecules to stimulate T cell activation

The mechanism underlying the apparent differences in the capacity of murine and human class I MHC molecules to function as signal transducing structures in T cells was examined. Crosslinking murine class I MHC molecules on splenic T cells did not stimulate an increase in intracellular calcium ([Ca²⁺]_i) and failed to induce proliferation in the presence of IL-2 or PMA. In contrast, modest proliferation was induced by cross-linking class I MHC molecules on murine peripheral blood T cells or human class I MHC molecules on murine transgenic spleen cells, but only when costimulated with PMA. Moreover, cross-linking murine class I MHC molecules or the human HLA-B27 molecule on T cell lines generated from transgenic murine splenic T cells stimulated only modest proliferation in the presence of PMA, but not IL-2. On the other hand, cross-linking murine class I MHC molecules expressed by the human T cell leukemic line, Jurkat, transfected with genes for these molecules, generated a prompt increase in [Ca²⁺]_i, and stimulated IL-2 production in the presence of PMA. The results demonstrate that both murine and human class I MHC molecules have the capacity to function as signal transducing structures, but that murine T cells are much less responsive to this signal.