A crucial role for B and T lymphocyte attenuator in preventing the development of CD4+ T cell-mediated herpetic stromal keratitis

PURPOSE To investigate the effect of the B and T lymphocyte attenuator (BTLA; CD272) on cluster of differentiation (CD)4(+) T cell-mediated corneal immunopathology during murine herpetic stromal keratitis (HSK). METHODS BALB/c mice were infected with the herpes simplex virus type 1 (HSV-1) KOS strain by corneal scarification. The levels of BTLA expression in CD4(+) and CD8(+) T cells in murine peripheral blood were determined by flow cytometry on days 0, 3, 7, 10, 14, and 21 after HSV-1 infection. BTLA expression in the infected cornea was detected by immunohistochemistry. BALB/c mice were injected intraperitoneally with recombinant plasmid DNA encoding BTLA (pBTLA), pcDNA3.1, or PBS on 0 and 7 days before infection and 7 days postinfection. The incidence and severity of stromal disease, tear film virus titers, and the delayed-type hypersensitivity (DTH) reaction were then compared among treated and control groups. The effects of pBTLA on CD4(+) T cells that infiltrated into infected corneas and on type 1 helper T-cell (Th1) cytokines (interferon-gamma [IFN-γ]) were evaluated. The levels of glycoprotein D (gD) mRNA in corneas were tested by real-time PCR. The eyes were examined histologically. RESULTS BTLA expression increased both in the corneas of HSV-1 infected mice and in CD4(+) T cells in the murine peripheral blood. Systemic administration of pBTLA resulted in a diminished incidence and severity of corneal lesions compared to controls. Treatment with pBTLA led to a decreased infiltration of CD4(+) T cells into infected corneas, and diminished Th1 responses in murine corneas, draining lymph nodes, and splenocytes. The pBTLA treated mice showed an impaired DTH response two weeks after HSV-1 infection compared to control mice. No differences were noted in tear film virus titers or gD mRNA levels in corneas among the experimental groups. CONCLUSIONS The results suggest that recombinant pBTLA plays a crucial role in preventing HSV-1 specific responses in CD4(+) Th1 cells in the infected corneas. Thus, BTLA, with immunosuppressive effects, may be a good candidate for treatment of HSK.