Systemic immune responses in Cytauxzoon felis-infected domestic cats.

To characterize systemic immune responses in Cytauxzoon felis-infected cats. Blood and lung samples obtained from 27 cats. Cats were allocated into 4 groups: cats that died of cytauxzoonosis, acutely ill C felis-infected cats, healthy survivors of C felis infection, and healthy uninfected cats. Serum concentrations of tumor necrosis factor-α and interleukin-1 β were measured and serum proteins characterized. Blood smears were stained immunocytochemically and used to assess immunoglobulin deposition. Immunohistochemical expression of CD18 and tumor necrosis factor-α were compared in lung tissues obtained from cats that died and healthy uninfected cats. A real-time reverse-transcription PCR assay for CD18 expression was performed on selected blood samples from all groups. Concentrations of both cytokines were greater and serum albumin concentrations were significantly lower in cats that died of cytauxzoonosis, compared with results for all other groups. Erythrocytes from acutely ill cats and survivors of C felis infection had staining for plasmalemmal IgM, whereas erythrocytes from the other groups did not. Increased staining of C felis-infected monocytes and interstitial neutrophils for CD18 was detected. The real-time reverse-transcription PCR assay confirmed a relative increase in CD18 expression in cats that died of cytauxzoonosis and acutely ill cats, compared with expression in other groups. Immunostaining for TNF-α in lung samples confirmed a local proinflammatory response. Results indicated immunopathologic responses were greater in cats that died of C felis infection than in cats that survived C felis infection.