This chapter discusses the lymphocyte trafficking and regional immunity. The chapter discusses the present understanding of tissue-selective lymphocyte trafficking, focusing in particular on the gut and its associated lymphoid tissues. The sophisticated cellular, developmental, and molecular mechanisms involved are discussed in the chapter with emphasis on the importance of these mechanisms for the understanding and manipulation of regional immune responses in the gastrointestinal tract. Lymphocytes are migratory cells, trafficking from their sites of origin in the bone marrow and thymus and homing to and recirculating through specialized lymphoid and extra lymphoid tissues in the periphery. Like all leukocytes, lymphocytes develop with characteristic trafficking properties. A central tenet of current thinking in the field is that this tissue-specific targeting of antigen-reactive populations must increase the efficiency of immune surveillance by circulating memory cells as well as enhancing local immune responses. From the perspective of regional physiology and pathology, selective trafficking may also provide a mechanism for segregating the specialized immune response modalities characteristic of intestinal versus systemic immune responses.
