It recognizes a non-polymorphic antigen of the HLA-DR, Ia region. LN-3 reacts with B-cells of the germinal centers and mantle zones. It also recognizes monocytes, macrophages, and interdigitating histiocytes. It is an excellent histiocytic marker in paraffin sections producing intense cytoplasmic staining. True histiocytic neoplasms are similarly positive. HLA-DR antigens also occur on a variety of epithelial cells and their corresponding neoplastic counterparts.
