Mice lacking expression of the chemokines CCL21-Ser and CCL19 (plt mice) demonstrate delayed but enhanced T cell immune responses

The paucity of lymph node T cells (plt) mutation leads to a loss of CCL21 a nd CCL19 expression in secondary lymphoid organs. pit mice have defects in the migration of naive T cells and activated dendritic cells into the T cel l zones of lymphoid organs, suggesting that they would have defects in T ce ll immune responses. We now demonstrate T cell responses in plt mice are de layed but ultimately enhanced. Responses to contact sensitization are decre ased at day 2 after priming but increased at day 6. After subcutaneous immu nization, antigen-specific T cell proliferation and cytokine production in pit mice are increased and remain markedly elevated for at least 8 wk. Comp ared with wild-type mice, a proportion of T cell response in pit mice are s hifted to the spleen, and prior splenectomy reduces the T cell response in draining lymph nodes. After immunization of plt mice, T cells and dendritic cells colocalize in the superficial cortex of lymph nodes and in splenic b ridging channels, but not in T cell zones. These results demonstrate that p it mice mount robust T cell responses despite the failure of naive T cells and activated dendritic cells to enter the thymus dependent areas of second ary lymphoid organs.