Tumor necrosis factor-alpha and virus expression in the central nervous system of cats infected with feline immunodeficiency virus

Cytokine disregulation has been implicated in the pathogenesis of lentivirus-induced diseases. In the present study, 18 specific pathogen free (SPF) cats were inoculated with feline immunodeficiency virus (FIV) Petaluma strain and sacrificed at different times post-infection. Five additional SPF cats were used as controls. The cell localization of the cytokine tumor necrosis factor alpha (TNF-alpha) in the central nervous system (CNS) was determined by immunohistochemical and morphometric analyses with a polyclonal rabbit anti-human TNF-alpha antibody. TNF-alpha and FIV RNA were measured using competitive reverse transcriptase polymerase chain reaction (PCR) assays and the number of proviral genomes was estimated by competitive PCR. Portions of frontal cortex were collected from each animal and both formalin-fixed and snap-frozen and stored at -80 degrees C until used. The results showed that TNF-alpha is present mainly in astrocytes and microglial cells. Morphometric analysis showed that areas of TNF-alpha production increased in the early phases of infection. Molecular analyses demonstrated that the kinetics of proviral loads in the CNS were comparable to what observed in lymph nodes and peripheral blood mononuclear cells, with the peaks in the early and late stages of infection. A positive correlation was found between viral parameters and TNF-alpha transcription, the strongest relationship was found between the transcription of the cytokine and viral RNA load. These results confirm that invasion of CNS by FIV occurs soon after virus exposure and that during this phase there is an increase of local viral loads with concomitant up-regulation of TNF-alpha expression. During the asymptomatic phase viral replication remains low in spite of the progression of CNS alterations. The dissociation between the viral load and the lesions observed suggests the importance of an indirect mechanism for the progression of these lesions, even if TNF-alpha seems to play a role particularly in the early phase of infection.