Detection of interleukin 1 in ascites from cats with feline infectious peritonitis

Expression profiles of immune mediators in feline Coronavirus-infected cells and clinical samples of feline Coronavirus-positive cats

Background

There are two biotypes of feline coronavirus (FCoV): the self-limiting feline enteric coronavirus (FECV) and the feline infectious peritonitis virus (FIPV), which causes feline infectious peritonitis (FIP), a fatal disease associated with cats living in multi-cat environments. This study provides an insight on the various immune mediators detected in FCoV-positive cats which may be responsible for the development of FIP.

Results

In this study, using real-time PCR and multiplex bead-based immunoassay, the expression profiles of several immune mediators were examined in Crandell-Reese feline kidney (CRFK) cells infected with the feline coronavirus (FCoV) strain FIPV 79–1146 and in samples obtained from FCoV-positive cats. CRFK cells infected with FIPV 79–1146 showed an increase in the expression of interferon-related genes and pro-inflammatory cytokines such as MX1, viperin, CXCL10, CCL8, RANTES, KC, MCP1, and IL8. In addition, an increase in the expression of the above cytokines as well as GM-CSF and IFNγ was also detected in the PBMC, serum, and peritoneal effusions of FCoV-positive cats. Although the expression of MX1 and viperin genes was variable between cats, the expression of these two genes was relatively higher in cats having peritoneal effusion compared to cats without clinically obvious effusion. Higher viral load was also detected in the supernatant of peritoneal effusions compared to in the plasma of FCoV-positive cats. As expected, the secretion of IL1β, IL6 and TNFα was readily detected in the supernatant of peritoneal effusions of the FCoV-positive cats.

Conclusions

This study has identified various pro-inflammatory cytokines and interferon-related genes such as MX1, viperin, CXCL10, CCL8, RANTES, KC, MCP1, IL8, GM-CSF and IFNγ in FCoV-positive cats. With the exception of MX1 and viperin, no distinct pattern of immune mediators was observed that distinguished between FCoV-positive cats with and without peritoneal effusion. Further studies based on definitive diagnosis of FIP need to be performed to confirm the clinical importance of this study.

TNF-alpha, produced by feline infectious peritonitis virus (FIPV)-infected macrophages, upregulates expression of type II FIPV receptor feline aminopeptidase N in feline macrophages

The pathogenicity of feline infectious peritonitis virus (FIPV) is known to depend on macrophage tropism, and this macrophage infection is enhanced by mediation via anti-S antibody (antibody-dependent enhancement, ADE). In this study, we found that TNF-alpha production was increased with viral replication in macrophages inoculated with a mixture of FIPV and anti-S antibody, and demonstrated that this culture supernatant had feline PBMC apoptosis-inducing activity. We also demonstrated that the expression level of the FIPV virus receptor, feline aminopeptidase N (fAPN), was increased in macrophages of FIP cats. For upregulation of TNF-alpha and fAPN in macrophages, viral replication in macrophages is necessary, and their expressions were increased by ADE of FIPV infection. It was demonstrated that a heat-resistant fAPN-inducing factor was present in the culture supernatant of FIPV-infected macrophages, and this factor was TNF-alpha: fAPN expression was upregulated in recombinant feline TNF-alpha-treated macrophages, and FIPV infectivity was increased in these macrophages. These findings suggested that FIPV replication in macrophages increases TNF-alpha production in macrophages, and the produced TNF-alpha acts and upregulates fAPN expression, increasing FIPV sensitivity.

Replication of feline coronaviruses in peripheral blood monocytes

Feline infectious peritonitis virus (FIPV) (Coronaviridae) causes the most lethal viral infection in cats: FIP. The related feline enteric coronavirus (FECV) causes mild enteritis. Why these feline coronaviruses manifest so differently in vivo is not known. In this study, infection kinetics (titres and antigen expression) of FIPV 79-1146, and FECV 79-1683, were determined in peripheral blood monocytes from 3 donor cats and compared to those in Crandell feline kidney (CrFK) cells. The infection kinetics in monocytes were host dependent. Monocytes from 1 cat were resistant to both FIPV- and FECV-infection. Monocytes from the other 2 cats could initially be infected by both FIPV and FECV but FIPV infection was sustained in monocytes of only one cat. FECV-infection was never sustained and viral production was up to 100 times lower than in FIPV-infected monocytes. In CrFK cells, FIPV and FECV infection kinetics did not differ. In monocytes of a larger cat population (n = 19) the 3 infection patterns were also found. Considering all 22 investigated cats, 3/22 were not susceptible for FIPV and FECV. The rest could be infected with FECV and FIPV but 10/22 cats had monocytes that only sustained FIPV infection and 9/22 sustained neither FIPV nor FECV infection.

In vivo cytokine response to experimental feline infectious peritonitis virus infection

Feline infectious peritonitis virus (FIPV) is a coronavirus that causes sporadic fatal disease in cats characterized by vasculitis, granulomatous inflammation and effusive pleuritis/peritonitis. Histologic changes in lymphoid tissues include lymphoid hyperplasia, lymphoid depletion, histiocytosis, and granuloma formation. Although viremia occurs, histologic lesions are not found uniformly throughout lymphoid tissues. We used experimental infection of cats with a highly pathogenic FIPV isolate, UCD8, to study histologic lesions, virus replication, and cytokine expression in multiple lymphoid tissues during the effusive phase of disease. Viral RNA was found in 76% of central tissues (mediastinal lymph node, spleen, mesenteric lymph node) examined, as compared to 27% of peripheral tissues (popliteal lymph node, cervical lymph node, femoral bone marrow). All tissues positive for virus replication also demonstrated lymphoid depletion. Generally, affected tissues had lower levels of IL-4 and IL-12–p40 mRNA and higher levels of IL-10 mRNA. Although no differences in IFN-γ or TNF-α mRNA were measured, TNF-α protein expression was greater in affected tissues and demonstrated a shift in the source of TNF-α from macrophages to lymphocytes. Together, these results colocalize FIPV replication, lymphocyte depletion in tissues, and alterations in cytokine transcription and translation. A possible role for TNF-α in the previously described FIPV-induced lymphocyte apoptosis is also suggested.

Antibody and cytokine responses in kittens during the development of feline infectious peritonitis (FIP)

Two recombinant FIPV spike proteins were assessed for their immunogenic properties in 8-week-old kittens, which were then challenged intranasally with FIPV 79-1146. Humoral responses were assessed by ELISA and serum neutralisation test. Changes in PBMC cytokine mRNA levels were detected by a reverse transcription, semiquantitative polymerase chain reaction assay (RT-sqPCR), assessing IL-2, IL-4, IL-6, IL-10, IL-12 and IFNgamma. All of the kittens developed clinical signs typical of FIP, which were confirmed on gross post mortem examination. The recombinant proteins induced little or no specific antibody response prior to challenge, and failed to alter the course of disease compared to controls. One week after virus challenge, the stimulated PBMCs showed small increases in the expression of IL-6 and IFNgamma mRNA, which correlated with a transient pyrexia. After this time expression of IL-6 mRNA remained unaltered but, as FIP developed, mRNA levels of IL-2, IL-4, IL-10, IL-12 and IFNgamma became markedly depressed.

Effect of thromboxane synthetase inhibitor on feline infectious peritonitis in cats

Two cats with abdominal effusion and anorexia were diagnosed as feline infectious peritonitis (FIP). We tried to evaluate the effect of thromboxane (Tx) synthetase inhibitor, ozagrel hydrochloride, on the progression of symptoms and clinicopathologic data characteristic to FIP. After administration of Tx synthetase inhibitor, improvement of appetite and activity, decreases of peritoneal effusion, reduction of leukocyte number to normal level, and improvement of hyper gamma-globulinemia were found in 2 cats with FIP. These findings suggest that the vasculitis in FIP can be successfully treated with Tx synthetase inhibitor which inhibits platelet aggregation.