Putative scheme for mucosal B-cell homing in humans. Depicted are graded pathways (arrows) presumably followed by mucosal B cells of any isotype activated in nasopharynx-associated lymphoid tissue (NALT) represented by human Waldeyer lymphoid ring (including palatine tonsils and adenoids), versus gut-associated lymphoid tissue (GALT) represented by Peyer patches and isolated lymphoid follicles (ILFs) scattered along the intestinal tract, particularly in the large bowel. The principal homing-molecule profiles of the respective B-cell populations (top compartments), and the adhesion/chemokine cues believed to direct the extravasation of effector B cells into various tissue compartments (boxes), are indicated.