title: Regulatory function of human CD4+ cytolytic T lymphocytes.
abstract: Allograft rejection is mediated by both CD4+ and CD8+ T cells. The lytic function of the classic CD8+ cytolytic T lymphocytes (CTL) occurs through recognition of allogeneic major histocompatibility complex (MHC) class I on the surface of the graft. CD4+ CTL recognize MHC class II through a direct recognition pathway or an indirect pathway where MHC peptides are presented in the context of self MHC class II. Lytic CD4+ cells may destroy graft tissue or, we hypothesize, the indirect CD4+ T cell may down regulate CD8+ CTL by recognition of donor MHC peptides presented by self MHC class II expressed on CD8+ T cells. To define the role of CD4+ CTL in allograft outcome we used a CD4+ CTL that is MHC class II restricted, recognizing human leucocyte antigen (HLA)-A1 and HLA-B8 peptides in the context of HLA-DR4. This line (MDSxA1/B8) will lyse DR4+ B lymphoblastoid cells (LCL) pulsed with HLA-A1/B8 peptides (amino acids 60-84 of the alpha1 domain of the MHC class I molecule). These T cells will also lyse peptide-pulsed antigen-specific T cell clones, both CD4+ and CD8+, that express HLA-DR4. These clones must process and present the MHC class I peptides for recognition and lysis to occur. These results suggest a possible mechanism to explain allograft tolerance. Lytic CD4+ T cells, that recognize donor HLA peptides through an indirect antigen presentation pathway, down-regulate donor-specific CTL through peptide-specific lysis resulting in graft tolerance.
authors.affiliation: Department of Surgery, Washington University School of Medicine, St Louis, Missouri 63110, USA.
authors.forename: N J
authors.initials: NJ
authors.lastname: Poindexter
authors.forename: M A
authors.initials: MA
authors.lastname: Smith
authors.forename: A E
authors.initials: AE
authors.lastname: Haynes
authors.forename: T
authors.initials: T
authors.lastname: Mohanakumar
mesh_terms: D017951:Antigen Presentation; D015704:CD4 Antigens / Q000276:immunology*; D002460:Cell Line; D015804:HLA-DR4 Antigen / Q000276:immunology; D006801:Humans; D010455:Peptides / Q000276:immunology; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
chemical_list: D015704:CD4 Antigens; D015804:HLA-DR4 Antigen; D010455:Peptides