Cellular distribution and costimulatory function of rat CD28. Regulated expression during thymocyte maturation and induction of cyclosporin A sensitivity of costimulated T cell responses by phorbol ester
Tacke, M.; Clark, G.J.; Dallman, M.J.; Hünig, T.
Journal of Immunology 154(10): 5121-5127
1995
ISSN/ISBN: 0022-1767 PMID: 7730618 Document Number: 442145
CD28 has been identified in man and mouse as a potent costimulatory receptor on T cells. We have generated a mAb, called JJ319, to rat CD28 and show that it is expressed on virtually all peripheral rat alpha-beta and on most gamma-delta T cells, and on about half of NK cells. In contrast to the mouse but as in humans, most immature CD4+8+TCR-low thymocytes express little or no CD28, whereas CD28 expression is high on TCR-intermediate and TCR-high cells. mAb JJ319 very effectively costimulates T cell proliferation and IL-2 secretion by resting rat T cells. In contrast to results obtained in mice and humans, phorbol ester did not synergize in T cell activation with CD28-specific mAb but even induced sensitivity to cyclosporin A in T cell cultures that were optimally costimulated by mAbs to the TCR and to CD28. This result points to a novel effect of protein kinase activation by phorbol ester on signal transduction by TCR plus CD28 costimulation which only becomes apparent if, as in the rat, the TCR-mediated signal cannot be replaced by phorbol ester.