Humoral immune responses of cats to mammalian type-C virus p30s

Natural and experimental cat sera were tested in radioimmune precipitation assays vs purified p30s from FeLV, RD114 and MuLV. Antibodies with specificity for FeLV p30 comparable to hyperimmune sera from heterologous species but of low titer were found in a high percentage of normal cats from households with a high incidence of FeLV and neoplasia. Sera from cats with neoplasms were generally negative. Cats immunized with FeLV gave low-level immune response, also of the same general specificity as heterologous hyperimmune sera. Cat sera do not normally show antibody to RD114 p30 although two immunized weanling cats produced low titered but highly specific p30 antibody. Thus, for both classes of feline type-C virus p30s, there is an evident capability of the cat to mount an immune response to natural or experimental exposure to the respective proteins. The magnitude of the response is between 100 and 1,000 fold below that seen in heterologous species. In contrast, cats immunized with MuLV p30 gave immune responses comparable to those seen in guinea-pigs, rabbits and goats. Several very old cats with carcinoma had antibody which preferentially precipitated MuVL p30. A competition assay using one such serum and labelled MuVL p30 was inhibited by FeVL, RD114, and MuLV p30s. This indicates that the assay is "interspecies" in nature. Among the possible explanations of this reaction category is that it represents antibody to the p30 of an as yet undefined class of feline type-C virus.