SOME ASPECTS OF HUMORAL AND CELLULAR-IMMUNITY IN NATURALLY-OCCURING FELINE INFECTIOUS PERITONITIS

Haematology, antibody titers and serum protein electrophoresis from 48 eats (34 effusive and 14 noneffusive forms) affected with feline infe ctious peritonitis (FIP) were studied and compared with those of 20 he althy cats. In the effusive form, antibody titers and protein electrop horesis in the effusions were analyzed. The distribution of the immune cells and of the virus in FIP lesions were also investigated immunohi stochemically with the avidin-biotin complex (ABC) method, using antib odies against the FIP virus (FIPV), myelomonocytic (MAC387) and lympho id (CD3, CD4 and CD8 for T-cells and IgM and IgG for B-cells) antigens . Seropositive animals (antibody titer>1:100) were present among both the FIP infected cats (73%) and the healthy cats (70%). Cats with effu sive FIP had neutrophilic leukocytosis (P>0.05), lymphopenia (P<0.01) and eosinopenia (P<0.001). In both effusive and noneffusive forms decr eased albumin/globulin ratio (P<0.001) with hypoalbuminemia (P<0.001), hyperglobulinemia (P<0.001) and increased alpha(2)- (P<0.05), beta- ( P<0.05) and gamma-globulins (P<0.001) were found. Hypergammaglobulinem ia was not related to the antibody titers, suggesting the presence of other proteins with gamma-motility (e.g. complement fractions). The el ectrophoretic pattern of the effusions was always similar to that of t he corresponding serum. Antibody titers higher than those of the corre sponding serum were often detected in the effusions. Immunohistochemic al findings were not related to the antibody titers, bur they were rel ated to the histological aspect of the lesions. In cellular foci of FL P lesions many virus-infected macrophages and few lymphocytes, mainly CD4(+), were found. Extracellular viral and myelomonocytic antigens we re also detectable in the foci with intercellular necrosis. Only few F IPV-infected cells were present at the periphery of the larger necroti c foci: in these lesions MAC387(+) cells were mainly neutrophils, with many MAC387(-) macrophages, probably due to their activated state; a small number of lymphocytes, with an increasing percentage of CD8(+) c ells was present. Lymphocytes were more abundant when cellular foci an d FIP-infected macrophages were centered around neoformed vessels, IgM and IgG exposing B-cells were always few and scattered. In conclusion the simultaneous analysis of body fluids and of the cellular composit ion of the lesions showed a complex immune status, on which type III a nd type IV hypersensitivity could coexist. (C) 1998 Elsevier Science B .V. All rights reserved.