Ia‐bearing cells promote the concanavalin A mitogenic response of la‐negative T cells

Nylon wool column‐purified T cell populations depleted of la‐bearing cells do not respond to the T cell mitogen concanavalin A (ConA). The response of this population can be restored by admixture of untreated nylon wool‐nonadherent T cells. These promoter cells express Thy‐1, are not sensitive to mitomycin C treatment and cannot be replaced with adherent spleen cells. Experiments using the T6 chromosome marker demonstrate that Ia‐depleted populations respond to ConA only in the presence of the Ia‐positive population.