The feline leukemia virus (FeLV) is a contagiously spread oncornavirus that causes malignant transformation of lymphoid cells. Feline cells transformed by FeLV produce a new cell surface antigen, the Feline Oncornavirus Associated Cell Membrane Antigen (FOCMA), which is a tumor-specific cellular antigen specified by, but not part of, the virion (Hardy, in press). An indirect immunofluorescent antibody test for FeLV antigens in leukocytes of peripheral blood indicates that approximately 90% of cats with lymphosarcoma (LSA) are infected with FeLV. In response to infection the cat may produce FeLV neutralizing and/or FOCMA antibodies.

In the present study functional levels of total complement (TCH50), C4, C2, and Factor B were determined in cat sera. Protein levels of C1q were estimated by radial immunodiffusion using monospecific antiserum against cat C1q. A total of 60 animals were studied, 32 of which were normal and FeLV negative.

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