Objective: To investigate the expression of cytokine in CD(4)(+) T helper type 1 (Th1) and T helper type 2 (Th2) cells in murine cornea during recurrent herpetic stromal keratitis (HSK) and its relationship with the HSK.
Methods: Seven weeks after corneal inoculation with HSV-1, the eyes of latently infected BALB/c mice were irradiated by UV-B and examined for the signs of inflammation and viral reactivation. The corneas of six mice with recurrent stromal disease and six controls were examined to detect the content of Th1 type cytokines (IFN-gamma and IL-12) and Th2 type cytokines (IL-4 and IL-10) on days 0, 3, 7, 10, 14, 21 and 28 after irradiation.
Results: Peak of the inflammation process of HSK, manifested by stromal opacification, occurred 7-14 days after viral reactivation in latently infected mice. In semi-quantitative RT-PCR analyses, IFN-gamma, IL-12 p40, IL-10 and IL-4 mRNA were expressed before and during the clinical course of recurrent HSK. The highest expression of IFN-gamma and IL-10 was revealed during the occurrence and development of corneal inflammation (3 -14 days after the reactivation of virus) with a decline at the recovering process (after 14 days). The expression of IFN-gamma and IL-10 was co-related with the degree of corneal opacification. Large amounts of IL-12 p40 mRNA were detected in the cornea 3 days after the virus reactivation and maintained over the whole course of observation. IL-4 levels increased at 3-14 days after the reactivation of virus and declined after day 14.
Conclusions: Th1 and Th2 cytokines present together throughout the course of the inflammatory process accompanying recurrent corneal HSV-1 infection, which is likely associated with a memory response to viral antigens. The expression of IL-10 mRNA parallels with the expression of IFN-gamma and is co-related with the degree of corneal inflammation. The damage and repair of corneal tissue in recurrent HSK may depend upon the balance between the destructive cytokines and protective cytokines at the site of virus reactivation.