SURFACE IG ON B-LYMPHOCYTES FROM CATTLE AND SHEEP

IgD, first demonstrated in humans, has been unequivocally shown to exi st in primates and rodents. In addition to IgM a second unique membran e isotype, generally considered to be IgD, has been demonstrated in a number of other species, including dogs and chickens. Because of its a ssumed widespread presence, it is widely accepted that IgD is phylogen etically conserved and therefore functionally important in B cell matu ration. In the present paper, we could not demonstrate IgD on bovine B cells derived from peripheral blood, lymph nodes, spleen and fetal sp leen by precipitation with anti-light chain antibodies. This lack of d etectable IgD was confirmed in peripheral blood B cells of sheep, and raises questions on the requirement for IgD in cell differentiation an d Ig secretion. At present it is not clear whether cattle (and sheep) are an exception in this context, Reports of the presence of IgD in di fferent species are largely based on the assumption that non-IgM surfa ce Ig is most likely IgD. Our data question this extrapolation and str ess the need for further isotype characterization of the surface Ig in different species, Lack of surface IgD has been observed in human and mouse B-1 cells, most of which express the surface marker CD5. The po ssibility that all bovine B cells belong to the B-l lineage is discuss ed.