title: Ontogeny of lymphocyte homing receptor expression in the mouse thymus.
abstract: The monoclonal antibody MEL-14 has been used in conjunction with immunohistology and multiparameter immunofluorescence to identify and characterize homing receptor-bearing thymocytes at various stages of embryonic and neonatal development. MEL-14hi thymocytes first appear at day 14 of gestation and come to represent about 40% of day 15 fetal thymocytes. Thereafter, the proportion of MEL-14hi thymocytes rapidly declines such that by birth (usually the 20th day of embryonic development) only about 2% of thymocytes are MEL-14hi. Although newborn thymocytes resemble adult thymocytes in this respect, the phenotypic characteristics of fetal and neonatal MEL-14hi thymocytes suggest that this unique subset undergoes a gradual transition from containing exclusively phenotypically immature cells in early gestation to containing predominantly phenotypically mature cells by young adulthood. Thus, virtually none of day 15 MEL-14hi fetal thymocytes are peanut agglutinin (PNA)lo, Ly-1hi, or either Lyt-2-/L3T4+ or Lyt-2+/L3T4-, whereas in the weeks that follow a steadily greater proportion of MEL-14hi thymocytes come to express this mature pattern (roughly 70% at 4 wk of age). Most day 15 MEL-14hi fetal thymocytes appear to express the functional homing receptor molecule, since day 15 fetal thymocytes bind to peripheral lymph node high endothelial venules about 40 to 50% as well as do adult mesenteric node lymphocytes, whereas adult thymocytes bind only about 5% as well. We have also identified a population of outer cortical MEL-14hi Lyt-2-/L3T4- lymphoblasts that appears during thymus regeneration 5 to 6 days after the administration of hydrocortisone. These lymphoblasts express the same phenotype as cells that constitute 40% of the day 15 fetal thymus and only 0.4% of normal adult thymocytes, implying that this particular subset may make up a significant fraction of thymocytes whenever there is a requirement for rapid expansion of the intrathymic and/or peripheral T cell pools. Taken together, these results are consistent with the notion that expression of the MEL-14-defined homing receptor may be closely linked to important intrathymic events that may occur early in T cell development and yet still have an overriding impact on the selection of those thymocytes that will serve as precursors of thymus emigrants.
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000276:immunology; D000945:Antigens, Differentiation, T-Lymphocyte; D000950:Antigens, Ly / Q000032:analysis; D000954:Antigens, Surface / Q000032:analysis; D002454:Cell Differentiation; D002465:Cell Movement; D005434:Flow Cytometry; D007124:Immunoenzyme Techniques; D051379:Mice; D008815:Mice, Inbred Strains; D011971:Receptors, Immunologic / Q000032:analysis*; D016201:Receptors, Lymphocyte Homing; D013601:T-Lymphocytes / Q000145:classification / Q000166:cytology / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology* / Q000196:embryology / Q000254:growth & development
chemical_list: D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte; D000950:Antigens, Ly; D000954:Antigens, Surface; D011971:Receptors, Immunologic; D016201:Receptors, Lymphocyte Homing