Distinct antigen trafficking from skin in the steady and active states

In antigen trafficking from the skin, it has been postulated that Langerhans cells/dendritic cells are activated after capturing exogenous antigens, up-regulate the expression of the chemokine receptor, CCR7, and migrate into lymphoid organs in response to the signaling of a chemokine, CCL21, which is expressed in lymphatic vessels and T cell zone stromal cells. Here we demonstrate that there is a distinct pathway of antigen trafficking from skin in the steady state that is independent of CCL21-CCR7 signaling. Employing melanin granules as an endogenous traceable antigen, we developed a system for visualizing antigen trafficking using mice with melanocytosis in the skin. We found the abrogation of antigen trafficking into regional lymph nodes (LN) in CCL21-Ser-deficient paucity of lymph node T cells (plt) mice in the active state induced by lipopolysaccharide injection, corresponding with previous reports, but normal accumulation of antigen in regional LN under steady-state conditions. These findings suggest that self-antigen is trafficking constitutively using pathway(s) other than that of the active state and the constitutive trafficking might regulate self-reactivity of the immune system.