The Regulation of Lymphocyte Traffic

Abstract

The distribution of lymphocytes among the tissues of the body is not random. Both the number and the representation of particular functional subsets of lymphocytes are carefully controlled, differing in each lymphoid organ or tissue in a manner that presumably reflects local immune requirements. The tissue distribution of lymphocytes is a function of lymphocyte class, of their previous history or stage of differentiation, and of their antigenic specificity. For example, those lymphocyte populations primarily responsible for humoral immunity (B cells) predominate in the spleen and in the gut-associated Peyer’s patches, whereas T cells, which are primarily regulatory and cytotoxic cells, are the major lymphocyte type in the peripheral lymph nodes and skin (Stevens et al. 1982; Streilein 1978). Functionally and antigenically defined T-cell subsets are also unequally distributed between mucosal and nonmucosal lymphoid tissues (Elson et al. 1979; Kraal et al. 1983). The distribution of certain effector and effector-precursor populations can be even more restricted: especially dramatic is the segregation of IgA- vs. IgG-expressing B cells. Surface IgA-bearing lymphocytes are highly represented in the mucosa-associated lymphoid organs, and the mucosal surfaces attract predominantly IgA-secreting plasma cells (Guy-Grand et al. 1974; reviewed by Lamm 1976). In nonmucosal sites, such as peripheral lymph nodes or the skin, IgA-bearing cells are rare, and most plasma cells secrete IgM or IgG. Lymphocytes can also segregate in vivo on the basis of antigen specificity: antigen-specific B and T cells are disproportionately represented in lymph nodes or spleen challenged with antigen (Kraal et al. 1982; Sprent 1980) and antigen-specific plasma cells accumulate in tissue sites of specific antigen deposition (Husband and Gowans 1978; Husband 1982).