Disparate effects of phorbol esters, CD3 and the costimulatory receptors CD2 and CD28 on RANTES secretion by human T lymphocytes

This study has examined the stimuli required for secretion of regulated upo n activation, normal T-cell expressed, presumed secreted (RANTES) from T ly mphocytes and found that stimuli such as phorbol 12-myristate 13-acetate (P MA), which are unable to support T-cell proliferation and interleukin-2 (IL -2) production, are nevertheless able to elicit strong secretion of RANTES. Conversely, stimuli such as CD2 and CD28 ligation, which are able to suppo rt T-cell proliferation, are unable to elicit RANTES secretion. Coligation of CD3 and CD28 drives T-cell proliferation to a similar degree as CD2 and CD28 coligation, yet also supports modest RANTES secretion. Furthermore, CD 28 ligation enhances the secretion of RANTES stumulated by PMA and this cos timulatory effect is abrogated by the phosphoinositide 3-kinase inhibitor w ortmannin. Our data also indicate that the observed effects of PMA on RANTE S secretion are probably due to activation of protein kinase C (PKC) isoenz ymes, since RANTES secretion was unaffected by the non-PKC activating 4 alp ha-phorbol ester, whilst the general PKC inhibitor Ro-32-0432 inhibits PMA- stimulated RANTES secretion. Moreover, the effect of PMA appears to be chem okine-specific because PMA was unable to increase secretion of the related CC chemokine MIP-1 alpha. Under stimulation conditions where increases in [ Ca2+](i) occur (e.g. PMA plus ionomycin or CD3 plus CD28 ligation) RANTES s ecretion can be severely reduced compared with the levels observed in respo nse to the phorbol ester PMA. Hence, whilst PKC-dependent pathways are suff icient for strong RANTES secretion, a calcium-dependent factor is activated which negatively regulates RANTES secretion. This correlates well with the observation that ligation of cytolytic T lymphocyte-associated antigen-4 ( CTLA-4) (expression of which has been reported to be dependent on a sustain ed calcium signal), inhibits RANTES secretion induced by CD3/CD28, but has no effect on PMA-stimulated RANTES secretion.