We used semiquantitative RT-PCR to monitor the expression of mRNA encoding cytokines (IL-1β6,IL-6,TNF-α, and IL-10) and IFN-γ in fresh isolated peripheral blood mononuclear cells (PBMCs), lymph node mononuclear cells (LNMCs), and mononuclear cells obtained after bronchoalveolar lavages (BALMCs), of four cynomolgus macaques inoculated intravenously with a pathogenic isolate of simian immunodeficiency virus (SIVmac251). To investigate the effects of the viral load on the expression of the cytokines, two monkeys received 30 mg kg⁻¹ day⁻¹ of didanosine (ddI). The two nontreated monkeys became infected and seroconverted, whereas the ddI-treated monkeys were completely protected as demonstrated by all criteria of diagnosis of SIV infection. Concomitant with the peak of viral replication (2 weeks after the experimental inoculation), high levels of IL-6 mRNA were produced in PBMCs, LNMCs, and BALMCs of the two placebotreated infected monkeys. Overexpression of TNF-α and IL-10 mRNAs was sometimes observed in LNMCs and BALMCs. A progressive overexpression of IFN-γ mRNA, starting 2 weeks after experimental inoculation, was observed in BALMCs from infected animals. Concurrently, a marked increase in the CD8⁺ lymphocyte percentage in the BAL fluids was detected by FACS analysis.

Thus, our results emphasize the importance of a comparative study of the expression of cytokines in different tissues. They suggest the interactions of monocyte/macrophage monokine production with viral replication, as well as the role of IFN-γ in the development of lung cellular immunity to SIV infection.