ABSTRACT
We studied the phenotype and distribution of “naturally” occurring CD4+ CD25+ T regulatory cells (CD4+ CD25+ nTreg cells) resident in rabbit conjunctiva, the main T-cell inductive site of the ocular mucosal immune system, and we investigated their suppressive capacities using herpes simplex virus type 1 (HSV-1)-specific effector T (Teff) cells induced during ocular infection. The expression of CD4, CD25, CTLA4, GITR, and Foxp3 was examined by reverse transcription-PCR, Western blotting, and fluorescence-activated cell sorter analysis in CD45+ pan-leukocytes isolated from conjunctiva, spleen, and peripheral blood monocyte cells (PBMC) of HSV-1-infected and uninfected rabbits. Normal conjunctiva showed a higher frequency of CD4+ CD25(Bright+) T cells than did spleen and PBMC. These cells expressed high levels of Foxp3, GITR, and CTLA4 molecules. CD4+ CD25(Bright+) T cells were localized continuously along the upper and lower palpebral and bulbar conjunctiva, throughout the epithelium and substantia propria. Conjunctiva-derived CD4+ CD25(Bright+) T cells, but not CD4+ CD25(low) T cells, efficiently suppressed HSV-specific CD4+ and CD8+ Teff cells. The CD4+ CD25(Bright+) T-cell-mediated suppression was effective on both peripheral blood and conjunctiva infiltrating Teff cells and was cell-cell contact dependent but independent of interleukin-10 and transforming growth factor β. Interestingly, during an ocular herpes infection, there was a selective increase in the frequency and suppressive capacity of Foxp3+ CD4+ CD25(Bright+) T cells in conjunctiva but not in the spleen or in peripheral blood. Altogether, these results provide the first evidence that functional Foxp3+ CD4+ CD25(Bright+) Treg cells accumulate in the conjunctiva. It remains to be determined whether conjunctiva CD4+ CD25+ nTreg cells affect the topical/mucosal delivery of subunit vaccines that stimulate the ocular mucosal immune system.
The Mucosal Immune System: Modulation by Microemulsion