Dendritic cells are accessory cells for the development of anti-trinitrophenyl cytotoxic T lymphocytes.

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Abstract
Dendritic cells (DC) are the critical accessory cells for the development of anti-trinitrophenol (TNP) cytotoxic T lymphocytes (CTL) in vitro. A model was developed in which nylon wool-nonadherent [mouse] spleen cells were used as the responding and stimulating cells, the latter having been TNP-modified and X-irradiated. Thy-1-bearing CTL developed in C57BL/6, B6D2F1 and CBA mice only when small numbers of DC were added. Maximal responses in 5-day cultures were achieved with 0.5-1 DC/100 responding T cells. The DC did not have to be TNP modified directly. Anti-Ia and complement inactivated accessory cells; similar treatment of the responders had no effect. DC exposed to UV radiation were ineffective but X-irradiated DC were fully active. Culture media from DC or from DC-nylon wool-passed spleen T-cell cocultures that contained abundant CTL would not substitute for viable DC. Enriched preparations of macrophages (M.vphi.) were obtained from blood, peritoneal cavity and spleens of BCG-immune and unprimed mice. M.vphi. added at doses of 0.2-4% were weak or inactive as accessory cells. The level of Ia antigens on test M.vphi. populations was quantitated and visualized by binding of a radioiodinated monoclonal anti-I-Ab,d antibody, clone B-21. M.vphi. that bore substantial amounts of Ia from all organs were weak accessory cells. Addition of M.vphi. to DC-T cell cocultures produced inhibitory effects, usually at a dose of 2% M.vphi.. In contrast, 0.5% Ia-bearing M.vphi. from BCG-immune boosted mice inhibited > 80% of the DC-mediated CTL response. Addition of indomethacin reversed M.vphi. inhibition and 10-9 M prostaglandin E2 blocked the indomethacin effect. Indomethacin restored a low level of accessory cell function in immune-boosted adherent peritoneal cells but not in preparations of monocytes and spleen M.vphi.. Small numbers of DC were identified in preparations of immune-boosted peritoneal cells and may have accounted for the observed accessory activity. Evidently, the development of anti-TNP CTL is an immune response in which: DC are the critical accessory cells; Ia-bearing M.vphi. are weak or inactive; and M.vphi. can inhibit DC-mediated response by an indomethacin-sensitive mechanism.