The spleen is fed by a single artery and does not receive afferent lymphatic drainage. The sheaths are associated with lymphoid follicles of similar organisation to the lymph node. The largest concentration of lymphoid tissue is, however, in the gut and other mucosal areas. Here aggregates of lymphoid tissue, similar to lymph nodes in organisation, constitute Peyer's Patches in the lamina propria of the small intestine, tonsils in the pharynx, and submucosal lymphoid follicles in the appendix and throughout the upper airways. A VERY simplified overview of an immune response You receive a cut.
Bacteria enter the wound.
Some of the dead bacteria or their breakdown products are taken up by the tissue resident dendritic cells. This causes them to migrate to the local lymph node via afferent lymphatics. Dendritic cells enter the node in the T cell areas. They become resident there displaying their 'wares' T cells enter the node from the blood, trafficking through the T cell area to the efferent lymph. B cells entering nodes from the blood must cross the T rich area in transit to the B cell rich areas.