Massive, sustained γδ T cell migration from the bovine skin in vivo

In all species studied so far, γδ T cells are abundantly present in epithelia. The functions of these cells are largely unknown. Using a lymph duct cannulation method, which is only possible in large animals such as cattle, we show that large numbers of γδ T cells, but not αβ T cells, are constitutively present in pseudoafferent lymph draining bovine skin. The γδ T cells, which are present in pseudoafferent lymph, use Vγ segments that are characteristic for bovine dermal γδ T cells, suggesting that these cells migrated from the skin. Further supporting the origin of these cells is the fact that fluorescent latex beads injected in the skin could be recovered in cells in the pseudoafferent lymph. The cannulation method is minimally invasive, and the lymph flow, which was sustained and remained essentially unaltered during 14 days, closely represents the in vivo situation. The γδ T cells could not be induced to produce IFN-γ, TNF-α, and IL-10, and they did not express costimulatory molecules, IL-2 receptor, and MHC Class II molecules. The level of γδ T cell egress was 6.7 × 10³ γδ T cells per cm² skin per hour, which is enough to deplete all γδ T cells from the skin within 46 h. As this massive γδ T cell migration was observed during 14 days, constant replenishment of these cells must take place. Our data suggest that γδ T cells in tissues fulfill more than exclusively local functions.