Expression of the T200 family of glycoproteins in canine malignant lymphoma.

High molecular weight surface proteins were examined in lymph node lymphocytes from five control dogs and 27 dogs with malignant lymphoma. Polyclonal rabbit antiserum was raised against a 210,000-dalton (210 K) membrane protein which was purified from a canine lymphoid tumor by preparative slab gel electrophoresis. Three high MW proteins at 210, 195 and 170 K and a common proteolytic fragment at 95 K were detected in the electrophoretically separated plasma membrane preparations by immunoblotting with polyclonal anti-210 K antiserum. Two antigenically distinct patterns were evident: 1) Type 1 lymphomas expressed a major 210 K peptide (with or without a minor 195 K component), and 2) Type 2 lymphomas lacked the 210 K form but had a 170 K or 195 K peptide singly or in combination. Immunoperoxidase staining of formalin-fixed, paraffin-embedded tissue sections demonstrated that the antigen was localized predominantly to the surface membrane of lymphocytes, and that canine lymphoma cells expressed a greater amount of the antigen than normal lymph node lymphocytes. It was concluded that these structurally and antigenically related high molecular weight proteins, based on their antigenic patterns, limited peptide analysis and tissue distribution, represent the canine homologue of the lymphocyte differentiation antigen known as T200.