Characterization of two monoclonal antibodies (UCL4D12 and UCL3D3) that discriminate between human mantle zone and marginal zone B cells
Two new monoclonal antibodies (MoAbs), UCL3D3 and UCL4D12 were obtained following immunization with follicular lymphoma (UCL3D3) or low‐grade primary B cell gastric lymphoma cells (UCL4D12). In normal splenic white pulp, tonsil and small intestinal Peyer's patches, UCL4D12 recognizes marginal zone B cells and a subpopulation of follicle centre cells, whereas mantle zone B cells are UCL4D12 negative. In contrast, UCL3D3 recognizes mantle zone B cells and follicular dendritic cells, but not marginal zone B cells or follicle centre B cells. Double‐immunofluorescence studies showed that in the splenic white pulp, these antibodies stain reciprocally. The majority of UCL3D3+ cells are slgM+ andsIgD+ whereas a higher proportion of UCL4D12+ cells express surface IgM (sIgM) but not surface IgD (slgD). Less than 10% of splenic B cells express both 3D3 and 4D12 antigens. None of the cell lines tested expressed either antigen. Functional studies showed that both antigens play a role in B cell activation as the MoAbs increase the mitogenic effect of Staphylococcus aureus Cowan I on tonsil B cells. This effect was maximal at 72 h in culture. TPA activation was reduced, and no effect was observed with anti‐immunoglobulin (anti μ) or CDw40 (G28.5). UCL3D3 and UCL4D12 did not show any stimulatory effect on their own. Biochemical studies show that both MoAbs recognize proteins of 80–90 kD under reducing conditions. These two MoAbs appear to recognize new B cell surface antigens which may be useful for identifying subpopulations of B cells.