MODULATION OF CYTOLYTIC T-CELL RESPONSES BY HEPARAN-SULFATE

Accumulating evidence suggests that the functional properties of alloa ctivated T cells may depend upon the microenvironment in which the T c ells reside. For instance, we showed previously that heparan sulfate, a biologically active polysaccharide present on cell surfaces and extr acellular matrices, modulates the proliferative responses of splenocyt es through enhancement of cytokine and prostaglandin production by mac rophages. Here we report that under conditions of suboptimal stimulati on, heparan sulfate causes discrete alterations in the functional resp onses of murine cytolytic T cells. When present in a 5-day mixed leuko cyte culture (MLC), heparan sulfate mediates an increase, from 3- to 1 0-fold, in T cell-mediated cytotoxicity. This increase is dose depende nt and most pronounced when heparan sulfate is present in the highest concentration during the first 24 hr of the culture period. On the oth er hand, when added during the last 48-72 hr of an MLC, heparan sulfat e decreases cytotoxicity by 3- to 30-fold. Neutralizing antibodies aga inst IL-1 alpha, but not antibodies against IL1 beta, IL-6, or TNF alp ha/beta, abrogate the heparan sulfate-mediated increase in cytotoxicit y, suggesting that the increase depended in part upon the production o f IL-1 alpha. However, studies in which exogenous IL-1 was added to ML C showed that increased cytoxicity was not due only to increased cytok ine production. Augmentation of cytotoxicity was in part independent o f T cell help, as depletion of CD4(+) cells from the responder populat ion before MLC, or addition of neutralizing anti-murine IL-2 antibodie s plus human IL-2 to the MLC, did not abrogate the stimulatory effect of heparan sulfate. Heparan sulfate-treated CD8(+) lymphoblasts isolat ed after 7 days in MLC demonstrated an increased cytotoxicity, elevate d intracellular serine esterase, and perforin levels compared with lym phoblasts from control MLC. The decrease in cytotoxicity observed when heparan sulfate was present during the last several days of an MLC wa s likely mediated by PGE(2), as elevated levels of PGE(2) were detecte d in MLC supernatants of heparan sulfate-treated cultures, and because the decrease was not observed in the presence of indomethacin. Our re sults are consistent with the idea that the metabolism of heparan sulf ate, an endogenous component of parenchymal tissues, may regulate the tempo and magnitude of alloreactive cytotoxic T cell responses.