FCoV type 1 viruses induced higher antibody titers than FCoV type 2, and were more frequently associated with clinical signs and/or feline infectious peritonitis. against TGEV, FCoV 1, and FCoV 2 and TGEV antigen detected the highest proportion of seropositive cats. We conclude that a vaccine against FCoV should be based on FCoV type 1-related antigens and that for serodiagnosis of FCoV infection TGEV should be used to attain the highest diagnostic efficiency. Tacrine HCl When serology is used in addition to clinical signs, hematology, and clinical chemistry results as an aid to diagnose clinical FIP, TGEV shows a diagnostic efficiency equal to that of a FCoV antigen. Intensive research has been done since the first description of the disease pattern of feline infectious peritonitis (FIP) in 1963 (21), and yet the epidemiology and the pathogenesis of the fatal disease FIP, which is caused by a coronavirus is still not fully understood. It was shown that FIP is the single most important infectious cause of death in young cats, resulting in the loss of 10% of seropositive kittens during the first year of life (6). As for the pathogenesis, it is generally accepted today that feline coronavirus (FCoV) and FIP-inducing viruses (FIPV) represent virulence variants of the same virus rather than separate virus species (39). Most FCoV mutants do not cause clinical signs, although present at high viral loads; only sporadically mutants are pathogenic and induce FIP (28). In some cases, FCoV infection was found to IL12RB2 induce mild enteric symptoms (27,39). It was postulated earlier that harmless FCoVs were restricted to Tacrine HCl the intestinal tract and that FIP development would result from the capability Tacrine HCl of a virus mutant to induce systemic infection (33). In the meantime, it was demonstrated by reverse transcription (RT)-PCR that FCoV generally induces systemic infection (10,24,28). Moreover, FCoV and FIPV have remained serologically and genetically indistinguishable. Antigenetically, coronaviruses are divided into five groups. Together with canine coronavirus (CCoV) and transmissible gastroenteritis virus (TGEV), FCoV belongs to group I. Cats seem susceptible to all group I coronaviruses (23). Some feline strains are thought to originate from recombinations of FCoV and other group I viruses, such as CCoV (16). Based on in vitro neutralization tests, FCoVs were further classified into two serotypes which differ in their growth characteristics in cell cultures and antigenetic relationship to TGEV and CCoV; however, both serotypes can cause FIP Tacrine HCl (7,32). The serological distinction of FCoV type 1 from type 2 is most likely associated with differences in the S gene sequence as monoclonal antibodies to the S protein readily differentiate the FCoV subtypes (20). Furthermore, FCoV types 1 and 2 have a different cell tropism which can be explained by changes in the S protein binding to different receptors as demonstrated previously (18). Cats recovering from FCoV infection develop especially high titers against the S protein. Many new strains have recently been isolated (1,4,15,17,25,35) and phylogenetic examination suggests a spectrum of strains ranging from very feline-like to more canine-like rather than two distinct serotypes (1,4,25). Whichever system is applied to classify FCoV, the association between certain FCoV strains and their ability to induce disease could not yet be elucidated. Knowledge of the serotype circulating in a given population is an important prerequisite for the development of a FCoV vaccine in that the vaccine should be closely related to the field viruses. The present study was initiated to determine the seroprevalence of FCoV types 1 and 2 in Switzerland and find potential associations between the serotypes and certain disease manifestations. In addition, we aimed to characterize the immune response during experimental infection with FCoV 1. == MATERIALS AND.