Published online before print January 18, 2007
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T cell migration from the bovine skin in vivo

* Department of Infectious Diseases and Immunology and
Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands; and
Institute for Animal Health, Compton, UK
1 Correspondence: Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 1, 3584 CL Utrecht, The Netherlands. E-mail: i.vanrhijn{at}vet.uu.nl
In all species studied so far, 
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 
T cells, but not
ß T cells, are constitutively present in pseudoafferent lymph draining bovine skin. The 
T cells, which are present in pseudoafferent lymph, use V
segments that are characteristic for bovine dermal 
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 
T cells could not be induced to produce IFN-
, TNF-
, and IL-10, and they did not express costimulatory molecules, IL-2 receptor, and MHC Class II molecules. The level of 
T cell egress was 6.7 x 103 
T cells per cm2 skin per hour, which is enough to deplete all 
T cells from the skin within 46 h. As this massive 
T cell migration was observed during 14 days, constant replenishment of these cells must take place. Our data suggest that 
T cells in tissues fulfill more than exclusively local functions.
Key Words: trafficking other animals T lymphocytes