Abstract
Although many relevant immune reactions are initiated in the lymph nodes, this compartment has not been systematically studied in humans. Analyses have been performed on immune cells derived from tonsils, but as this tissue is most often inflamed, generalization of these data is difficult. Here, we analyzed the phenotype and function of the human CD4(+) T-cell subsets and lineages in paired resting lymph node and peripheral blood samples. Naive, central memory cells and effector memory cells as well as Th1, Th2, Th17 and Treg cells were equally represented in both compartments. On the other hand, cytotoxic CD4(+) T cells were strikingly absent in the lymph nodes. CXCR5(+)CD4(+) T cells, representing putative follicular Th (Tfh) cells were over-represented in lymph nodes and expressed higher levels of Tfh markers than their peripheral blood counterparts. Compared with the circulating pool, lymph-node-derived CXCR5(+)CD4(+) T cells were superior in providing help to B cells. Thus, functionally competent Tfh cells accumulate in resting human lymph nodes, providing a swift induction of naive and memory antibody responses upon antigenic challenge.