B cell localization and migration in health and disease

B lymphocytes are a highly dynamic cell population. During their lifetime they travel over distances that are many times larger than their own size. Mature B cells constantly travel throughout the body, patrolling for antigens. This migration process is tightly regulated through a system of chemokines and adhesion molecules, which act like address codes to bring the B cells to their destination in various tissues. Moreover, already during their maturation process in the bone marrow, B cells of various developmental stages are undergoing distinct changes in their localization. This chapter focuses on the localization of various B cell subsets and on how their migration, adhesion, and interactions with tissue-resident stromal cells are regulated on a molecular level to ensure an efficient humoral immune response against pathogens. Apart from their role in protective immune responses, the same mechanisms that guide the motility of B cells can be detrimental under certain circumstances (e.g., in chronic inflammation and lymphoma dissemination)