Assessment of the role of leucocyte function-associated antigen-1 in homotypic adhesion of activated B lymphocytes

In this study we investigated how T-cell-dependent stimuli, via interleukin -4 (IL-4) or CD40 ligation, influence homotypic B-cell adhesion when compar ed with induction by the T-cell-independent stimulus lipopolysaccharide (LP S). Using primary murine B cells, we Found that T-cell-dependent stimulatio n led to increased aggregation as compared to that induced by LPS. The adhe sion was to a large extent dependent on the adhesion molecule, lymphocyte f unction-associated antigen-1 (LFA-1). We found that activation of B cells w ith the mitogenic stimuli induced an increased avidity of LFA-1 for its lig and, intercellular adhesion molecule-1 (ICAM-1). The increase was stable an d different from that induced by phorbol esters. Although adhesion was redu ced using B cells from LFA-1-/- mice, aggregation occurred in response to T -cell-dependent stimuli. Our data suggest that adhesion of B lymphocytes is regulated in different modes. One is induced by antigen and leads to a tra nsient conformational change of the LFA-1 molecule. Another is induced by m itogenic stimuli and leads to stable avidity increase of LFA-1, possibly vi a activation of cytoskeletal anchorage. A third is LFA-1 independent, of lo w avidity and is induced by T-cell-dependent stimuli.