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Modulation of CD8⁺ CTL Effector Function by Fibroblasts Derived from the Immunoprivileged Cornea

¹From the Graduate Program in Immunology and the ²Departments of Ophthalmology, ³Molecular Genetics and Biochemistry, and ⁴Immunology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.

PURPOSE. To examine the acquisition of lytic activity and interferon gamma (IFN-) production by herpes simplex virus (HSV) type 1-specific CD8⁺ cytotoxic T-lymphocyte precursors (HSV-CTLps) after exposure to in vitro HSV-1-infected fibroblasts derived from the immunoprivileged cornea (HSV-cFb) or nonprivileged skin (HSV-sFb) or to in vitro HSV-1-infected splenocytes (HSV-Spls) obtained from noninfected mice.

METHODS. Chromium release assays were used to assess HSV-CTL cytotoxicity, and flow cytometry was used to assess intracellular granzyme (Gr) B content and lytic granule exocytosis through surface CD107a expression. In addition, the BLT esterase assay was used to assess functional GrA release. [³H]-Thymidine incorporation and total CD8⁺ cell numbers, as assessed by flow cytometry, were used to assess CTLp proliferation. ELISA and intracellular flow cytometric analysis were used to assess CTL IFN- production and release.

RESULTS. HSV-cFb, HSV-sFb, and HSV-Spl individually induced strong cytotoxic and IFN- responses by HSV-CTL. Simultaneous exposure to HSV-Spl and HSV-cFb virtually abrogated the cytotoxic response while enhancing IFN- production by HSV-CTL. In contrast, exposure to HSV-sFb, in conjunction with HSV-Spl, did not alter the cytotoxic or IFN- response of HSV-CTL compared with stimulation with either cell type alone. Abrogation of the cytotoxic response after simultaneous exposure to HSV-Spl and HSV-cFb was associated with reduced production, storage, or both of GrA and GrB but with unimpaired lytic granule release.

CONCLUSIONS. These findings suggest that an interesting regulatory circuit protects the cornea from the potentially damaging effects of CD8⁺ T-cell cytotoxic function while maintaining their ability to control virus replication through enhanced production of the antiviral cytokine IFN-.