Analysis of T cell activation requirements with the use of alloantigens or an anti-clonotypic monoclonal antibody.

H-2Kb-specific alloreactive cytotoxic T lymphocyte (CTL) clones, which secrete macrophage-activating factor (MAF) in response to antigen, were used to study the antigenic and physiologic parameters for T cell-antigen receptor (Ti)-mediated activation. When H-2Kb was presented on untreated, formaldehyde (FOR)-fixed cells, or liposomes, optimal stimulation in the absence of co-factors was obtained only with the untreated cells. FOR cells, which were efficient inhibitors of CTL-target cell interactions for the CTL clones studied, had a greatly reduced activating capacity. Phorbol myristic acetate (PMA), which alone had no activating effect on the CTL clones, acted in synergy with FOR cells, restoring an unimpaired H-2Kb-dependent activation for some CTL clones. H-2Kb-liposomes were not stimulatory even in the presence of PMA and/or splenic feeder cells. For one H-2Kb-specific CTL clone (KB5-C20), activation was studied with the use of an anti-clonotypic (anti-Ti) monoclonal antibody (mAb), Désiré-1. By using this immunoglobulin (Ig) G2a mAb or its F(ab')2 or Fab fragments, it was observed that the association constant of the IgG2a (4.7 X 10(9) M-1) for KB5-C20 was 30-fold higher than that of the Fab fragment, whereas the molar concentration of mAb required to inhibit 50% of the H-2Kb-specific CTL activity of clone KB5-C20 was 70-fold to 90-fold higher for the Fab fragment than for the IgG2a (1 to 5 X 10(-10) M). It was also observed that activation as measured by MAF secretion of clone KB5-C20 was obtained by using the divalent IgG2a mAb or its F(ab')2 fragment at 10(-9) M to 10(-8) M in the absence of any added co-factor or feeder cells, whereas a 500-fold higher molar concentration of the Fab fragment only induced very low levels of MAF secretion. Also, in the presence of PMA, the mAb-mediated activation of MAF secretion by clone KB5-C20 was increased, but Fab-induced activation never resulted in high titers of MAF. We conclude that the intrinsic "affinity" of the H-2Kb-Ti interaction is probably so low for the Ti of clone KB5-C20 that efficient activation by H-2Kb is obtained only when multivalency is achieved on H-2Kb-expressing cells, and possibly when molecules on the T cells such as Lyt-2 and LFA-1 stabilize the interactions.(ABSTRACT TRUNCATED AT 400 WORDS)