Haematological and serum protein profiles of cats with different lesions and viral antigen distribution in feline infectious peritonitis

HAEMATOGICAL AND SERUM PROTEIN PROFILES OF CATS WITH DIFFERENT LESIONS AND VIRAL ANTIGEN DISTRIBUTION IN FELINE INFECTIOUS PERITONITIS Paltrinieri S., Grieco V.*, Comazzi S., Teti M.*, Parodi Cammarata M.* Istituto di Patologia Generale Veterinaria, and *Istituto di Anatomia Patologica Veterinaria e Patologia Aviare, via Celoria 10, Milano, Italy; Feline Infectious Peritonitis (FIP) is characterized by different clinical forms, by lesions with different evolutive pattern, and by a high variability in viral antigen distribution. In order to investigate if these different patterns are associated with differences in immunological status, we analyzed haematologic and serum protein profiles of cats with different pathologic findings. Cats with the effusive form had lower number of circulating lymphocytes, higher levels of - and - globulins and lower levels of -globulins, compared to those with non-effusive forms. Among the cats with effusive forms, -globulins and antibody titers were lower in cats with histologic features referrable to acute lesions. These findings are signs of a non specific inflammatory status in the acute effusive forms; in the subacute effusive forms and in the non effusive FIP an immune mediated reaction predominates. Furthermore, cats with effusive FIP had lower albumin levels, most likely due to the sequestration of these proteins in the effusions. The distribution of viral antigen showed the greatest variation between the cats, with differences in the percentage of positive foci, in the amount of viral antigen within the lesions and in the localization of the virus (within the cells or in the extracellular necrosis). A decrease in circulating lymphocytes was found in cats with the highest percentage of positive foci, in those with stronger positivity and in presence of extracellular viral antigen. These findings are consistent with both the hypothesis that the lack of cellular immunity can exacerbate the disease and that severe FIP infection induces lymphocyte depletion. Furthermore, the presence of viral antigen in the extracellular necrosis is associated with an increase in the number of blood neutrophils. Low - and high -globulin levels were found in cats with high percentage of positive foci (these also had high antibody titers), in those with stronger positivity and in those with both extracellular and intracellular antigen. This suggests that the larger is the amount of viral antigen, the stronger is the involvement of the immune system and that early necrosis activates the immune system. Finally, strong differences in serum protein levels were found between cats with and without viral antigen in germinal centers of lymph nodes draining the lesions. The latter had higher levels of  and -globulins and lower -globulins, together with lower amount of circulating immunecomplexes, suggesting the presence of the virus in the lymph nodes in the acute phase of the disease. In conclusion, a non specific inflammatory reaction characterizes the cats with acute effusive lesions, with low levels of viral antigen, detectable intracellularly in a small number of foci and in the lymph nodes. In contrast, specific immunity and lymphocyte depletion characterizes the cats with the subacute effusive form or with non-effusive FIP, with higher amount of viral antigen, higher number of positive foci and an extracellular positivity.