Lack of beta 2-microglobulin on the surface of canine transmissible venereal tumor cells.

beta 2-Microglobulin (beta 2m) expression on the cell surface of the naturally occurring, allotransplantable canine transmissible venereal tumor (TVT) was investigated by use of indirect membrane immunofluorescence and radioimmunoassay. Two cell populations were identified in animal-derived, collagenase-disaggregated TVT cell suspensions. About 80% of the cells lacked surface beta 2m expression, whereas about 20% of the cells strongly reacted with anti-dog beta 2m serum. With the use of a cell separation technique, beta 2m-negative cells were demonstrated to carry TVT markers on their surface, whereas the beta 2m-positive cells did not express the tumor markers. The beta 2m-positive cells seemed, therefore, to be tumor-infiltrating host cells. These findings were supported by fluorescence staining studies of frozen sections of the TVT. The lack of beta 2m expression on the surface of TVT cells might explain the allotransplantability of this neoplasm, since beta 2m expression on the cell surface appeared to be obligatory for the expression of class I major histocompatibility complex antigens.