Differences between Primed Allogeneic T‐Cell Responses and the Primary Mixed Leucocyte Reaction

Abstract

Recent investigations have demonstrated that the primary mixed lymphocyte reaction (MLR) is dependent on certain accessory molecules, e.g. CD4 and LFA-1. We have compared the requirements of the primary MLR and the responses of alloreactive, primed lymphocytes (PL) by inhibition studies using monoclonal antibodies (MoAb) directed against (i) adhesion molecules belonging to the CD11 cluster of leucocyte antigens (CD11a, LFA-1; CD11b, MAC1=CR3; and CD11c, p 150.95); (ii) various T cell-related antigens(CD2, CD4, CD5 and CD8); and (iii) recombinant IL-1β. The CD5-, CD11a- and CD11c-reactive MoAb significantly inhibited the primary MLR (inhibition = 25%, P0.01; 48%, P0.01, and 13%, P0.05, respectively) but these MoAb did not inhibit the primed lymphocyte reaction (PLR). The CD11b-reactive MoAb had no significant influence on either of the responses. CD2- and CD4-reactivc MoAb significantly inhibited both primary MLR (>80%, P0.01) and to a lesser extent the PLR (40–65%, P0.01). A MoAb reactive with IL-1β inhibited the primary MLR (38%, PP0.01) of peripheral blood mononuclear cells (PBMC), whereas primed allogeneic responses to PBMC and Epstein-Barr virus (EBV) cell lines were unaffected by this MoAb. In addition, preliminary data indicated that PL seemed neither to bind exogenous IL-1 (as opposed to CD4⁺ PBMC) nor to possess membrane-bound IL-1. The differences between ‘virgin’ and primed, allogeneic T-cell responses indicate that profound changes in the functional capability of the responding T-cell population take place during the bulk expansion. The results indicate that during repeated priming with alloantigen and bulk expansion, the proliferative response of T lymphocytes becomes independent of (i) the interaction with the CD11 adhesion molecule(s). (ii) the CD5 molecule, and (iii) the cytokine IL-1β.