The influence of LFA 1 on human T cells stimulated by solid-phase immobilized HLA class II-peptide complexes

Purified HLA class II-peptide complexes immobilized to a solid support induce proliferation of human T-cell clones, indicating that human T-cell clones can proliferate in the absence of secondary signals from accessory cells. We hypothesized that T cells can provide co-stimulatory signals to T cells. LFA-1 molecules play an important role in homotypic interactions of T cells and murine monoclonal antibodies reactive with LFA 1 can inhibit T cell-T cell interactions. LFA-1 reactive monoclonal antibodies inhibited cytolysis of peptide-pulsed T cells by T cells and partially inhibited T-cell proliferation. To study the direct effect of the LFA 1 molecule on T-cell activation, we co-immobilized HLA-class II-peptide complexes with LFA-1 reactive MoAbs. Co-immobilization resulted in an enhanced proliferative response of the T-cell clones. This could indicate that the LFA 1 molecule on T cells is not a passive adhesion molecule, but is capable of transducing a signal that synergizes with the stimulatory signal via the T-cell receptor.