CD4+ T-cell type 1 and type 2 cytokines in the HSV-1 infected cornea

· 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 105 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-1α (IL-1α), type 1 cytokines (IL-2, interferon-γ) 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-1α, IFN-γ and IL-2 mRNA were found in the eyes at days 1 and 2 p.i. IL-1α protein was detected in the conjunctiva, limbus and corneal epithelium at day 2. The IL-1α staining intensities increased with disease progression. This was paralleled by IL-2 and IFN-γ 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-γ, 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-γ. Type 2 cytokines participate in the late stage of inflammation and might be useful to improve the course of the disease.