UCL3D3 and UCL4D12 reactivity in small B-cell neoplasms with special emphasis on monocytoid B-cell lymphoma

Two recently described monoclonal antibodies, UCL3D3 and UCL4D12, have been reported to have some specificity for mantle zone B lymphocytes and marginal zone/follicular center B lymphocytes, respectively, in the spleen. Forty-nine B-cell neoplasms, including 20 cases of monocytoid B-cell lymphoma (MBCL), were studied by frozen section immunohistochemistry with these antibodies to evaluate their utility. Tonsil, lymph node, and reactive spleen also were studied with the antibodies. Although a wide overlap was observed among the different lymphomas, a majority of cases of MBCL and half of cases of hairy cell leukemia (HCL) reacted with both markers, suggesting both marginal/follicular and mantle cell antigen expression. None of four cases of mantle cell lymphoma reacted with the proposed mantle cell marker UCL3D3, whereas three of these cases immunoreacted with UCL4D12. This marker is known to react with a subpopulation of follicular center cells and possibly with marginal zone lymphocytes. A comparison of nodal and extranodal neoplasms failed to show a significant difference in the pattern of immunoreactivity with these antibodies. Tonsil and lymph node controls showed some mantle zone staining with both antibodies, and there was a slight overlap in mantle and marginal zone staining of the spleen controls. These findings suggest an immunologic similarity between some cases of HCL and MBCL. However, the findings also would suggest that these antibodies, particularly UCL4D12, have less specificity than has been previously assumed, and UCL4D12 may not have practical utility in the evaluation of low grade B-cell lymphomas.