Distinct Homing Pathways Direct T Lymphocytes to the Genital and Intestinal Mucosae in Chlamydia-infected Mice

Immunity to genital tract infection with Chlamydia trachomatis is mediated by type 1 CD4+ T lymphocytes. To define the signals that govern lymphocyte trafficking to the genital mucosa, integrins expressed by infiltrating T cells and endothelial addressins displayed on local vasculature were characterized during the course of infection. All T cells expressed the alphaLbeta2 heterodimer that binds vascular ICAM-1, and most displayed enhanced levels of the alpha4beta1 integrin that interacts with VCAM-1. AlphaE and beta7(low) integrin chains were detected on approximately 15 and 30% of infiltrating T cells, respectively. Lymphocytes derived from the spleen or draining lymph nodes expressed this same integrin profile, suggesting that cells are recruited to the genital mucosa from the systemic circulation without significant selection pressure for these markers. Immunofluorescent staining for the corresponding vascular addressins revealed intense expression of VCAM-1 on small vessels within Chlamydia-infected genital tracts and up-regulation of ICAM-1 on endothelial, stromal, and epithelial cells. Mucosal addressin cell adhesion molecule-1 was not detected within genital tissues. These results indicate that T lymphocyte homing to the genital mucosa requires the interaction of alphaLbeta2 and alpha4beta1 with endothelial ICAM-1 and VCAM-1, respectively, which is the same pathway that directs lymphocytes to systemic sites of inflammation. Homing pathways defined for the intestinal mucosa and assumed to be relevant to all mucosal sites are not well represented in the genital tract. The identification of T lymphocyte trafficking pathways shared between systemic and mucosal tissues should facilitate vaccine strategies aimed at maximizing immune responses against Chlamydia and other pathogens of the urogenital tract.