Investigation of acute phase proteins and some immune parameters in cats with different titers of feline coronavirus seropositivity

Feline infectious peritonitis (FIP) is a systemic and progressive disease in cats, caused by infection with feline coronavirus (FCoV), and is most often fatal. The non-specific nature of clinical and laboratory findings complicates the diagnosis and leads to the disease being recognized at a late and/or end stage. The aim of this doctoral thesis is to identify potential important biomarkers for the early diagnosis of FIP by evaluating FCoV antibody titers in conjunction with acute phase proteins (Alpha-1 acid glycoprotein [AGP], Serum amyloid A [SAA], C-reactive protein [CRP], Haptoglobin [Hp]) and Feline interferon gamma (IFN-γ) levels, and to reveal the risk of subclinical FIP in asymptomatic cats with high antibody titers. Between 2021 and 2024, a total of 84 cats over 1 year of age, regardless of breed or sex, are referred to the Internal Medicine Depertment Polyclinics, Istanbul University-Cerrahpasa, with complaints of anorexia, lethargy, diarrhea, vomiting, jaundice, and/or general condition impairment, were included in the study. The cats were divided into seven groups (S0, S1, S2, S3, S4, S5, and S6) according to their FCoV antibody titers determined by the Immunocomb® ELISA method, and clinical, hematological, biochemical, and immunological parameters were evaluated in detail in all groups. The effects of age, breed, and sex on FCoV infection and the development of FIP were examined in detail. It was determined that the risk of developing FIP may be increased in cats under 2 years of age, as well as in British Shorthair and Scottish Fold breeds, and that male cats more frequently exhibited higher feline coronavirus antibody titers and clinical symptoms specific to FIP. High antibody titers were found to be associated with increased AGP and SAA levels, whereas IFN-γ levels were higher in the negative and low-positive titer groups. This finding supports the significant role of the cellular immune response in the pathogenesis of FIP. In conclusion all parameters examined in this study show that they can provide significant contributions to the differential diagnosis of FIP, veterinary clinical practice and espesially to the survival and the quality of life of cats infected with feline coronavirus.