Macrophage-T interactions are required for the Con A-induced generation of human Ts capable of inhibiting PHA-induced blastogenesis among autologous PBMC. Con A treatment of adherent cell-depleted PBMC, or PBMC recovered after a 7-day incubation in FCS, failed to generate Ts. Addition of adherent cells to either of these populations restored Con A inducible Ts. Discontinuous density gradient fractionation of adherent cells demonstrated that the required accessory cell was a low density macrophage bearing the human equivalent of murine Ia.

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