Reduced constitutive cytokine transcription in isolated monocytes of clinically healthy cats, infected with an FIV strain of low pathogenicity

Twenty-five barrier-maintained cats had been experimentally infected for 9.5 months with an FIV strain of low pathogenicity, FIV Zurich 2. Animals were clinically healthy and did not exhibit any haematological changes. FIV proviral DNA was demonstrated in peripheral blood lymphocytes of all cats and in monocytes of most animals, identifying FIV Zurich 2 as a both lympho- and monocytotropic strain. Monocytes were isolated from FIV-infected cats as well as from age-matched uninfected control cats, short-term cultured and examined for cytokine (IL-1β, IL-6, IL-10, IL-12 p40 and TNF-α) transcription by real-time PCR. Constitutive transcription of cytokines in monocytes from FIV-infected cats was restricted to IL-1β and, in the majority of samples, TNF-α. For all cytokines, transcription levels were significantly lower in FIV-infected cats than in control cats. Transcription was often least intense in those samples where FIV infection of the monocyte fraction was not demonstrated. Results show that infection of cats with an FIV strain of low pathogenicity was associated with depression of constitutive cytokine transcription in monocytes even if clinical and haematological changes were not observed.