title: The priming of helper T cells.
abstract: Before helper T cells and B cells can interact to produce specific antibody, the antigen-specific helper T cell precursors must be primed. Priming is a fairly abrupt event which occurs in vivo about 5 days after immunization. Priming involves several steps: Antigen uptake, processing, and cell surface expression bound to class II MHC molecules by an antigen presenting cell, recirculation and antigen-specific trapping of helper T cell precursors in lymphoid tissue, and T cell proliferation and differentiation. Helper T cells express CD4, but not all CD4 T cells are helper cells. The signals required for clonal expansion of helper T cells differ from those required by other CD4 T cells. The critical antigen-presenting cell for helper T cell priming appears to be a macrophage, and the critical second signal for helper T cell growth is the macrophage product interleukin-1.
authors.affiliation: Section of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Janeway
mesh_terms: D000818:Animals; D000917:Antibody Formation / Q000276:immunology*; D017951:Antigen Presentation; D005802:Genes, MHC Class II / Q000276:immunology; D007156:Immunologic Memory; D008264:Macrophages / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology*; D018417:Th1 Cells / Q000276:immunology; D018418:Th2 Cells / Q000276:immunology
chemical_list: D011948:Receptors, Antigen, T-Cell