Lymph node B lymphocyte trafficking is constrained by anatomy and highly dependent upon chemoattractant desensitization.

B lymphocyte recirculation through lymph nodes (LNs) requires crossing endothelial barriers and chemoattractant-triggered cell migration. Here we show how LN anatomy and chemoattractant receptor signaling organize B lymphocyte LN trafficking. Blood-borne B cells predominately used CCR7 signaling to adhere to high endothelial venules (HEVs). New B cell emigrants slowly transited the HEV perivenule space, and thereafter localized nearby, avoiding the follicle. Eventually, the newly arrived B cells entered the basal portion of the follicle gradually populating it. In contrast, newly arriving activated B cells rapidly crossed HEVs and migrated toward the lymph node follicle. During their LN residency, recirculating B cells reacquired their sphingosine-1 phospate receptor 1 (S1P1) receptors and markedly attenuated their sensitivity to chemokines. Eventually, the B cells exited the LN follicle by entering the cortical lymphatics or returning to the paracortical cords. Upon entering the lymph, the B cells lost their polarity, down-regulated their S1P1 receptors, and subsequently strongly up-regulated their sensitivity to chemokines. These results are summarized in a model of homeostatic trafficking of B cells through LNs.