title: B lymphocytes in vivo fail to prime naive T cells but can stimulate antigen-experienced T lymphocytes.
abstract: The ability of B cells or macrophages and dendritic cells (DC) to elicit class II-restricted T cell responses in vivo was compared using a mouse chimera model. Severe combined immunodeficient (SCID) mice (H-2d), reconstituted either with T or T+B lymphocytes from (H-2d x H-2b) donors, were immunized subcutaneously with protein antigen (Ag) to induce a class II-restricted T cell response. The frequency and major histocompatibility complex restriction of the resulting Ag-specific T cells were analyzed to establish whether B cells were necessary for the induction of class II-restricted T cell responses, and to determine the cell type on which priming had occurred. The results indicated that: (a) B cells are not necessary for the induction of a class II-restricted T cell response in vivo, as the frequencies of interleukin 2 (IL-2)- or IL-3-secreting T cells induced in the presence or absence of B cells were comparable. (b) Activation of naive T cells requires presentation of Ag on DC; Ag presented only on B cells is not sufficient to elicit a response. No H-2b-restricted, IL-3-secreting cells could in fact be detected in SCID mice reconstituted with naive (H-2d x H-2b) T cells and nonimmune or antigen-primed (H-2d x H-2b) B cells. (c) Previously primed T cells are able to be stimulated by Ag presented by both B cells and DC. H-2b-restricted, IL-3-secreting cells could in fact be readily demonstrated in SCID mice reconstituted with antigen-primed (H-2d x H-2b) T and B cells. Irrespective of whether the T cells were naive or previously activated, B cells were able to respond with an Ag-specific immunoglobulin G response, indicating that B cells were functional and able to present Ag in order to receive specific T cell help. Therefore, it appears that B cells are not necessary and do not participate in the initial priming of T cells; however, Ag presented by B cells can reactivate previously primed T cells. Taken together, these data indicate that during the course of an immune response Ag is first presented to naive T cells via DC, and only subsequently primed T cells can be stimulated by Ag presented by B cells.
authors.affiliation: Basel Institute for Immunology, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Ronchese
authors.forename: B
authors.initials: B
authors.lastname: Hausmann
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D000941:Antigens / Q000008:administration & dosage / Q000494:pharmacology*; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D002450:Cell Communication / Q000502:physiology; D002478:Cells, Cultured; D002678:Chimera; D004797:Enzyme-Linked Immunosorbent Assay; D006183:H-2 Antigens / Q000032:analysis; D064532:Histocompatibility Antigen H-2D; D000949:Histocompatibility Antigens Class II / Q000032:analysis*; D007376:Interleukin-2 / Q000378:metabolism; D007377:Interleukin-3 / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D008954:Models, Biological; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism / Q000502:physiology*
chemical_list: D000941:Antigens; D006183:H-2 Antigens; D064532:Histocompatibility Antigen H-2D; D000949:Histocompatibility Antigens Class II; D007376:Interleukin-2; D007377:Interleukin-3