Inhibitory action of sulfatide, a putative ligand for L-selectin, on B cell proliferation and Ig production

The interaction of L-selectin and its ligand is widely accepted to mediate leukocyte rolling and adhesion on the endothelial surface. Although L-selectin is ubiquitously expressed on lymphoid cells, its role in execution of lymphocyte functions is unknown. By flow cytometric analysis using mAb specific for sulfatide, a putative ligand for L-selectin, we found that sulfatide was selectively expressed on B cells, but not on T cells. To elucidate the involvement of L-selectin and its ligand in B cell activation, the present study was undertaken to investigate effects of sulfatide on T celldependent and -independent Ig production by B cells. In pokeweed mitogen-stimulated cultures, addition of sulfatide resulted in almost complete inhibition of Ig production by B cells in the presence of memory CD4+ T cells, whether L-selectin-positive or -negative. A similar inhibition of Ig production by sulfatide was found when B cells were stimulated with Staphylococcus aureus Cowan I and IL-2. Unlike sulfatide, a desulfated form of sulfatide, galactosylceramide, did not show any effects on Ig production by B cells. Maximal inhibition of Ig production was observed when sulfatide was added at the early period of culture. Sulfatide suppressed effectively proliferation of B cells, but not of T cells. Sulfatide competed the binding of anti-L-selectin mAb to B cells, suggesting it could interfere B cell activation by blocking L-selectin function. The results suggest a novel role of the L-selectin/its ligand system in the initiation of B cell activation.