Evidence for functional relevance of CTLA-4 in ultraviolet-radiation-induced tolerance

Hapten sensitization through W-exposed skin induces hapten-specific toleran ce that can be adoptively transferred by injecting T lymphocytes into naive recipients. The exact phenotype of T cells responsible for inhibiting the immune response and their mode of action remain unclear. Evidence exists th at CTLA-4 negatively regulates T cell activation. We addressed whether CTLA -4 is involved in the transfer of UV-induced tolerance. Injection of lymph node cells from mice that were sensitized with dinitrofluorobenzene (DNFB) through W-irradiated skin inhibited induction of contact hypersensitivity a gainst DNFB in the recipient animals, When CTLA-4(+) cells were depleted, t ransfer of suppression was lost. Likewise, significantly fewer lymphocytes enriched for CTLA-4(+) cells were necessary to transfer suppression than un fractionated cells. Expression of CTLA-4 appears to be functionally relevan t, since in vivo injection of a blocking anti-CTLA-4 Ab was able to break U V-induced tolerance and inhibited transfer of suppression. Upon stimulation with dendritic cells in the presence of the water-soluble DNFB analogue, D NBS, CTLA-4(+) T cells from DNFB-tolerized mice secreted high levels of IL- 10, TGF-beta, and IFN-gamma; low levels of IL-2; and no IL-4, resembling th e cytokine pattern of T regulatory 1 cells. Ab blocking of CTLA-4 resulted in inhibition of IL-10 release. Accordingly, transfer of tolerance was not observed when recipients were treated with an anti-IL-10 Ab, Hence we propo se that T cells, possibly of the T regulatory 1 type, transfer UV-mediated suppression through the release of IL-10. Activation of CTLA-4 appears to b e important in this process.