Alteration of cytokine levels in murine retrovirus infection: modulation by combination therapy.

Immunoregulatory cytokines may regulate the resistance or susceptibility of a host to retroviral infection. These cytokines may be therapeutically modulated to prevent or limit the progression of infection. The non-progression to AIDS of some HIV+ patients has been related to a strong type 1 cytokine response (IL-2, IL-12, and IFNgamma). For this reason, we investigated the ability of combination therapeutics to modulate cytokines in vivo towards a type 1 cytokine response in a murine retroviral infection using Friend leukemia virus (FLV). BALB/c mice were infected with FLV and treated with either 3'-azido-3'-deoxythymidine (AZT), the immunomodulator methionine enkephalin (MENK), or a combination of both AZT and MENK starting 3 d post infection. Splenocytes were harvested on days 1, 3, 7, 14, 21 and 28 post treatment initiation and cultured with 1 microg/ml concanavalin A (ConA) for 24 h. Supernatants were examined for IL-2, IL-4, IL-10, IL-12, and IFNgamma cytokine production using cytokine specific ELISAs. The levels of type 2 cytokines were not significantly changed by any treatment group over the course of the disease. However, although decreased in all infected animals, type 1 cytokines were partially maintained by the combination treatment through day 21. RT-PCR for cytokine specific mRNA confirmed these results, with expression of the type 1 cytokines, especially IFNgamma, being maintained through day 21. Establishment of a treatment regime that can maintain protective cytokine activities against disease progression may prove applicable to other retroviral infections.