Regulation of virus induced inflammatory immune responses with cytokine DNA

Viral infection frequently results in chronic inflammatory lesions the principal mediators of which are proinflammatory molecules from activated T cells. Controlling these events has been a focus of the clinical field. Although cytokine therapy using some regulatory cytokines such as IL-10 or TGFβ represents one of the most promising approaches, proteins have a short half-life and bioactivity in vivo, making the strategy inconvenient and costly. In this study, cytokines expressed by means of plasmid DNA were evaluated for their efficacy to modulate inflammatory responses and the mechanisms by which such modulation occurred were investigated. Both mucosal and systemic administration of plasmid DNA encoding IL-4 or IL-10 prior to HSV infection inhibited the development of cutaneous inflammatory responses. To achieve modulation of ocular inflammation administration close to the eye itself provided best results. In the case of cytokine DNA administration to already HSV-primed animals (therapeutic approach), only plasmid DNA encoding IL-10 showed a regulatory effect on the expression phase of the cutaneous DTH response. The mechanisms of immune modulation following prophylactic administration of plasmid DNA encoding IL-4 showed a shift the Th subset balance toward Th2 responses. In contrast, both prophylactic and therapeutic administration of plasmid DNA encoding IL-10 downregulated the activity of Thi response. The delivery systems for the therapeutic modulation of cutaneous inflammatory response were also compared. Plasmid DNA encoding IL-10 had a delayed and milder, yet more persisting effect than that achieved by viral vectors expressing IL-10. Moreover, plasmid DNA was not affected by preexisting immunity as occurred following administration of viral vectors. Finally, the studies on the mechanism of modulation by plasmid DNA encoding IL-10 revealed that multiple mechanisms such as active suppression, induction of energy or inhibition of ARC appeared to be involved. Although wide dissemination, even to the inflammatory sites and transgene expression occur following in vivo inoculation of plasmid DNA, the central T cell regulation appeared to be the principal mechanism for immune modulation by IL-10 DNA.