Purpose: It has been previously shown that CD4+ T-lymphocytes are critical mediators in HSV-1 stromal keratitis (HSK). CD4+ T cell subpopulations (type 1, type 2) can be defined by their capabilities of producing different sets of cytokines. This study was performed to determine the role of type 1 and type 2 cytokines in murine HSK.
Methods: BALB/c mice (n = 20) were inoculated with 10(5) PFU of HSV-1 (KOS strain) and were followed clinically. At various time points post-infection (p.i.), the conjunctival and corneal tissues were analyzed histologically (n = 2 each time point), and immunohistochemically (n = 5 each time point) for the presence of interleukin-1alpha (IL-1alpha), type 1 cytokines (IL-2, interferon-gamma) and a type 2 cytokine (IL-4). The expression of cytokine mRNA was tested in eye samples by reverse transcription-polymerase chain reaction (RT-PCR).
Results: Stromal keratitis clinically progressed after day 9. In 15% of the mice, disease regressed until day 14 p.i. Polymorphonuclear neutrophils, lymphocytes and other mononuclear cells infiltrated the conjunctiva by day 2 and rapidly expanded to the central cornea between days 7 and 14. IL-1alpha, IFN-gamma and IL-2 mRNA were found in the eyes at days 1 and 2 p.i. IL-1alpha protein was detected in the conjunctiva, limbus and corneal epithelium at day 2. The IL-1alpha staining intensities increased with disease progression. This was paralleled by IL-2 and IFN-gamma staining intensities. In contrast, IL-4 mRNA and protein were detected at days 7 through 14 after HSV-1 infection; compared to IL-2 and IFN-gamma, IL-4 staining intensities were lower.
Conclusions: The findings suggest that the lymphocytic infiltrate during the development of HSV-1 keratitis is predominantly composed of type 1 cells expressing IL-2 and IFN-gamma. Type 2 cytokines participate in the late stage of inflammation and might be useful to improve the course of the disease.