T cell activation by cross‐linking anti‐CD3 antibodies with second anti‐T cell antibodies: dual antibody cross‐linking mimics physical monocyte interaction

Abstract

The anti‐CD3 antibody BMA030 (IgG_2a isotype) induces T cell activation and proliferation if an interaction with monocytes is provided. In contrast to other anti‐CD3 antibodies, it is unable to induce interleukin (IL)2 responsiveness through cross‐linking by plastic‐bound goat anti mouse Ig antibodies (panning). Cross‐linking BMA030 with a second anti‐T cell antibody is, however, able to induce IL 2 responsiveness in monocyte‐depleted T cell cultures. In this report we show that a large number of different antibodies are suitable for this dual antibody stimulation, and that the extent of proliferation corresponds to the percentage of T cells expressing the respective T cell antigen. Proliferation induced by low concentrations (0.1‐1 ng/ml) of other anti‐CD3 antibodies requires also cross‐linking with second anti‐T cell antibodies. The proliferative response of monocyte‐depleted T cells to two cross‐linked anti‐T cell antibodies plus added IL 2 is of the same magnitude as the one induced by anti‐CD3 antibodies plus monocytes. On the other hand, if monocytes are present, soluble anti‐CD2, ‐CD4, ‐CD8, ‐LFA‐1 antibodies (IgG₁ or F(ab′)₂ fragments) can inhibit OKT3 or BMA030‐induced T cell activation. Anti‐CD6 antibodies do not interfere with this monocyte‐dependent T cell stimulation. We conclude that dual antibody stimulation mimics the physical contact of T cells with monocyte membranes, where the T cell receptor CD3 complex is cross‐linked with neighboring structures (mainly so‐called adhesion molecules) through the interaction with respective counter‐structures on monocyte membranes. Dual antibody cross‐linking bypasses this interaction and can be used to stimulate IL2 responsiveness of antibodydefined T cells.