Suppression of stimulating cell activity by microtubule-disrupting alkaloids.

Microtubule-disrupting alkaloids and protein fixatives were used to investigate the nature of an active process that must occur within stimulator cells in order for them to initiate a unidirectional mixed lymphocyte response (MLR). Brief treatment of the stimulator cells (SC) with glutaraldehyde (0.15%), formalin (0.6%), or lanthanum chloride (10-3 M) abolished their capacity to activate responder cells (RC). Pretreatment of SC with microtubule-disrupting alkaloids, colchicine (c) (10-4 to 10-6 M) or colchicine + vincristine (c+v) (10-4 to 10-6 M) also abrogated their stimulating capacity. This capacity was not restored by the addition of supernates from untreated cultures, thereby excluding the possibility that the alkaloids acted by decreasing the release of soluble stimulatory factors from SC. The introduction of alkaloid-inactivated, mitomycin-treated RC as drug carriers did not affect the mitogenic response of untreated RC to concanavalin A. This excluded a significant leakage of alkaloids from the treated SC and uptake by RC during culture. Lumicolchicine produced no decrease in the stimulating capacity of SC. This suggested that the suppression induced by low concentrations of colchicine resulted from its specific disruption of microtubules. None of the above treatments quantitatively reduced the antigenicity of SC, as evaluated by humoral and cell-mediated lysis of the treated cells. Also, these treatments produced no significant changes in the specific binding of concanavalin A by SC. These results indicate there is a functional interaction of microtubular structures with cell surface antigens that appears to regulate either the capacity of SC to associate with RC, or the ability of SC to form and stabilize stimulatory antigenic configurations on the cell surface.