Ia-bearing cells promote the concanavalin A mitogenic response of Ia-negative T cells.

Nylon wool column-purified T cell populations depleted of Ia-bearing cells do not respond to the T cell mitogen concanavalin A (Con A). The response of this population can be restored by admixture of untreated nylon wool-nonadherent T cells. These promotor 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.