Distribution of Interleukin-22–secreting Immune Cells in Conjunctival Associated Lymphoid Tissue

Purpose: Interleukin (IL)-22 is a cytokine involved in epithelial cell regeneration. Currently, no research studies have analyzed the distribution of the three distinct IL-22–secreting cell populations in human or mouse conjunctiva. This study investigated the distribution of the three main populations of IL-22–secreting immune cells, αβ Th cells, γδ T cells, or innate cells (innate lymphoid cells [ILCs] or natural killer cells), in conjunctival associated lymphoid tissues (CALTs) in human and mouse models. Methods: We collected discarded cadaveric bulbar conjunctival tissue specimens after preservation of the corneo- limbal tissue for keratoplasty from four enucleated eyes of the domestic donor. The bulbar conjunctiva tissue, including the cornea from normal (n = 27) or abraded (n = 4) B6 mice, were excised and pooled in RPMI 1640 media. After the lymphoid cells were gated in forward and side scattering, the αβ Th cells, γδ T cells, or innate lymphoid cells were positively or negatively gated using anti-CD3, anti-γδ TCR, and anti–IL-22 antibodies, with a FACSCanto flow cytometer. Results: In normal human conjunctiva, the percentage and number of cells were highest in αβ Th cells, followed by γδ T cells and CD3– γδ TCR – IL-22+ innate cells (presumed ILCs, pILCs) (Kruskal-Wallis test, p = 0.012). In normal mice keratoconjunctiva, the percentage and total number were highest in γδ T cells, followed by αβ Th cells and pILCs (Kruskal-Wallis test, p = 0.0004); in corneal abraded mice, the population of αβ Th cells and pILCs tended to increase. Conclusions: This study suggests that three distinctive populations of IL-22–secreting immune cells are present in CALTs of both humans and mice, and the proportions of IL-22+αβ Th cells, γδ T cells, and pILCs in CALTs in humans might be differently distributed from those in normal mice.