EXPRESSION OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II ANTIGEN IN NEOPLASTIC-CELLS OF CANINE CUTANEOUS HISTIOCYTOMA

Forty five cases of canine cutaneous histiocytoma (CCH) were examined by immunohistology for expression and distribution of major histocompa tibility complex (MHC) class II antigen in neoplastic cells. In additi on, expression of lysozyme and calprotectin (leucocyte protein L1) in neoplastic cells was investigated. Furthermore, B and T lymphocytes we re demonstrated by antibodies against the CD3 antigen, IgG, and IgM. N eoplastic cells showed two staining patterns for MHC class II antigen: focal juxtanuclear cytoplasmic staining and/or rim-like staining alon g the cell periphery. In 24 cases, a predominant or exclusive focal ju xtanuclear cytoplasmic MHC class II antigen reaction in neoplastic cel ls, and the presence of few diffusely distributed infiltrating CD3 ant igen-positive T lymphocytes were observed. Tumors with numerous neopla stic cells exhibiting staining for MHC class II antigen along the cell periphery (n=21) showed increased inflammatory alterations, represent ed by disseminated and nodular infiltrations of mainly CD3 antigen-pos itive T cells. B cells, plasma cells, exudate macrophages, and neutrop hils were rarely seen disseminated between neoplastic cells whereas th eir number increased within focal inflammatory infiltrates, The focal cytoplasmic reaction for MHC class II antigen in neoplastic cells migh t represent newly synthesized MHC class Il molecules stored in vesicle s, whereas staining of the cell periphery might occur due to accumulat ion of MHC class II molecules along the plasma membrane. The increasin g expression of MHC class II molecules on the cell surface might be th e decisive factor for onset and progression of tumor regression. Howev er, the exact mechanism of priming and activation of T cells by neopla stic cells and the nature of the presented antigen are not yet known. (C) 1998 Elsevier Science B.V.