Studies on T lymphocyte activation II. The target cells for concanavalin A‐induced growth factors

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Abstract
Growth factors contained in Con A(concanavalin A)‐conditioned media (CM) maintain exponential growth in T cell blasts derived from mitogen stimulation of spleen cells with Con A, phytohemagglutinin, lentil lectin and pokeweed mitogen (PWM), as well as from mixed lymphocyte reactions to H‐2 D or I‐E and I‐C‐encoded determinants and from non‐H‐2 Mls locus‐controlled reactions. Such growth factors are strictly T cell blast‐specific, inasmuch as they do not stimulate resting, small T or B lymphocytes nor B cell blasts generated by lipopolysaccharide or lipoprotein activation. The responsiveness of T cell blasts to CM appears to be the result of the availability on the cell surface of an acceptor site for growth factors which is not expressed in resting cells, because T cell blasts, but not small spleen cells, absorb out the growth‐promoting activity contained in CM. Furthermore, lectins such as Con A and PWM interfere with the blast surface membrane in such a way that they inhibit the response to growth factors. Finally, there is no detectable allotypic or isotypic restriction in the activity of Con A‐CM on a variety of target T cell blasts.