Inhibition of expression of cell-mediated immunity by a cell surface-binding antibody directed against T-cell helper factors.

In this study, the effects of a monoclonal antibody, AF3.44.4, which is directed against antigen-specific, T-cell-derived helper factors, were investigated in two models of T-cell-macrophage co-operation. In vitro, cultures of nylon-wool-enriched peritoneal cells from mice immune to Listeria monocytogenes (T cells), macrophages from normal mice and Listeria antigen produced an activity mitogenic for mouse thymocytes (TMF). When AF3.44.4 was added to such cultures, the production of this activity was inhibited in a dose-dependent fashion. Preincubation of T cells with AF3.44.4, followed by its removal, was not sufficient for the inhibitory effect to be manifested. In an in vivo system, when spleen cells from Listeria-immunized mice were transferred to unprimed mice, the latter were protected against subsequent challenge with Listeria. Treatment of spleen cells with AF3.44.4 prior to transfer did not affect their ability to confer resistance upon recipients. It is postulated that AF3.44.4 acts on a population of T cells that is involved in macrophage-T-cell co-operation in vitro and that this population may be different from that involved in macrophage T-cell co-operation in vivo.