The role of mitogenic lectins in T-cell triggering

Abstract

THE process of T-lymphocyte activation requires the participation of metabolically active non-θ-bearing accessory cells¹. As first conclusively shown by Habu and Raff², this requirement is also true of lectin-dependent triggering. Thus, T-cell activation by mitogenic lectins depends on the presence of la-positive non-T cells^3,4. The mere binding of lectins such as concanavalin A (Con A) to the surface membrane of T cells does not trigger the cells to go through the mitotic cycle. This can only be achieved by the activity of growth factors present in conditioned media (CM) from Con A-stimulated cell cultures⁵. Such growth factors, however, cannot activate normal, resting T cells, although they are competent to maintain activated T cells in exponential growth for indefinite periods of time⁶. Hence, to be mitogenic a lectin must not only induce the in situ production of T-cell growth factors, but must also render resting T cells sensitive to the mitogenic activity of these growth factors. In this report we demonstrate that the binding of Con A to purified T cells can in a relatively short time, modify their functional sensitivity to growth factors, even though this binding is not sufficient to stimulate them to proliferate.