Anti-leucocyte function-associated antigen-1 antibodies inhibit T-cell activation following low-avidity and adhesion-independent interactions.

Anti-leucocyte function-associated antigen-1 (LFA-1) antibodies can provide either stimulatory or inhibitory signals to T cells, depending on the epitope they recognize, type and stage of activation of the T cells, and nature of the activation stimulus. Because of the low affinity of interaction between the T-cell receptor (TcR) and the antigen/major histocompatibility complex (MHC), it was proposed that the LFA-1 molecule strengthens the adhesion between the interacting cells, thus contributing in an additive manner to TcR-specific interactions. To check if high-avidity, TcR-specific interactions still require the accessory function of the adhesion molecule, we studied the effect of anti-LFA-1 antibodies on T-cell triggering mediated through chimeric receptors composed of an Fv of an antibody and a constant region of the TcR. Such chimeric TcR (cTcR) confer on T cells antibody-type specificity and affinity. We made use of transfected T-cell hybridomas expressing various amounts of either one cTcR chain (composed of VH linked to C beta) or double-chain cTcR (VHC beta + VLC alpha). When such transfectants were stimulated with hapten-modified cells, anti-LFA-1 antibodies inhibited activation predominantly mediated through cTcR composed of a single chimeric chain and did not inhibit stimulation of the double-chain transfectants. Moreover, these anti-LFA-1 antibodies blocked antigen-specific T-cell activation regardless of whether the stimulus was adhesion dependent or not, such as in the case of stimulation by immobilized hapten-protein conjugates. These studies show that the 'off-signal' provided by anti-LFA-1 antibodies is adhesion independent and affects mainly low-avidity TcR-antigen interactions.