Clearance of feline leukemia virus from persistently infected pet cats treated by extracorporeal immunoadsorption is correlated with an enhanced antibody response to FeLV gp 70.

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Abstract
Six persistently feline leukemia virus (FeLV)-infected pet cats were treated by extracorporeal immunoadsorption with Staphylococcus aureus Cowan I (SAC) to remove circulating immune complexes and immunoglobulin G (IgG) from plasma. In three of these cats, the FeLV infection was eliminated, whereas in the other three cats the infection persisted. The amounts of peripheral blood leukocyte (PBL)-associated FeLV, soluble FeLV envelope glycoprotein (gp70) antigens in serum, and FeLV-gp70-specific antibodies were determined in all six cats at different times during treatment. In all of the cats, there were fluctuations in the amounts of FeLV-positive PBL and of serum antigen related to FeLV gp70. The one serologic parameter that always correlated with complete clearance of FeLV in the responder cats was the development of free antibodies to gp70. These results suggest that extracorporeal immunoadsorption treatment stimulates an existing low level antibody response to FeLV in some cats, and that these antibodies mediate the clearance of FeLV. The results also suggest that determination of antibody titer to FeLV is of value in predicting the outcome of extracorporeal immunoadsorption treatments as well as when treatment may be terminated.