THE VALUE OF IMMUNOHISTOCHEMISTRY
IN THE ASSESSMENT OF BONE MARROW DISORDERS

Attilio Orazi, M.D., FRCPath. and Dennis P. O'Malley, M.D.

CD45RB (Leucocyte Common Antigen) Leucocyte Common Antigen is a mouse monoclonal antibody made against human peripheral blood lymphocytes. We use the epitope PD7/26. This epitope reacts with both B and T lymphocytes and with monocytes and macrophages. It also reacts weakly with granulocytes, but because of the striking difference in reactivity between lymphoid and myeloid cells it is effectively a lymphocyte marker. We find that a heat induced epitope retrieval technique is preferable and find that the antibody works well with either formalin or B5-fixed tissue and does not appear to be affected by decalcification. Leucocyte common antigen is a valuable antibody to document the hematologic nature of a given proliferation. It is relatively specific, but may be negative in some kinds of malignant lymphomas, most notably Hodgkin's disease, anaplastic large cell lymphoma, and in B- cell lymphomas with significant plasmacytoid differentiation (e.g. immunoblastic lymphoma). References Warnke RA, Gatter KC, Falini B, et al: Diagnosis of human lymphoma with monoclonal antileucocyte antibodies. N Engl. J Med 1983;309:1275.