Two new monoclonal antibodies (LN-4,LN-5) reactive in B5 formalinfixed,Paraffin-embedded tissues with subsets of macrophages and B lymphocytes and derived tumors.

We have studied two new monoclonal antibodies that are effective in BS-fixed paraffin-embedded sections using ABC immunoperoxidase technique and show predominant reactivity with cells of the mononuclear-phagocyte system.LN-4 has specificity for phagocytic macrophages and epithelioid histiocytes among hematopoietic cells. LN-S demonstrated a wider range of hematopoietic reactivity. It stained macrophages and some dendritic cells, including interdigitating reticulum cells and Langerhans cells and also reacted with some B-Iymphocytes,most strongly with mantle zone B-cells. Selectively, LN-4 and LN-5 gave positive reactivity with some cases of true histiocytic lymphoma and histiocytosis X. These two new antibodies will be useful in confirming histiocytic disorders, particularly in cases for which fresh or frozen tissue is not available.