title: Differential recognition by CD28 of its cognate counter receptors CD80 (B7.1) and B70 (B7.2): analysis by site directed mutagenesis.
abstract: CD28, which is a member of the immunoglobulin superfamily of molecules (IgSF), is a homodimer of two polypeptides containing a single V-like domain with short transmembrane and cytoplasmic regions. It serves as a co-signalling molecule for T cell activation through binding to its cognate counter-receptors CD80 and B70, expressed on antigen presenting cells. In the current study, we investigated the regions of CD28 which are involved in its interactions with CD80 and B70, using site directed mutagenesis, CD28 mAb epitope mapping, receptor based adhesion assays and direct binding of Ig-fusion proteins to cell surface receptors. Truncation or substitution of a stretch of a proline rich "hallmark" sequence, "MYPPPY", abrogates binding to CD80 or B70, while retaining CD28 mAb epitopes and cell surface expression. On an Ig-fold model of the CD28 V-domain, this fully conserved motif localizes to a CDR3-like region. Mutations introduced into other loops, including the CDRI-like and CDR2-like regions, had very little effect on CD80 or B70 binding. Mutations introduced within the predicted beta-strand regions caused loss of receptor expression. Conservative substitution of both the flanking tyrosine residues within the "MYPPPY" motif with phenylalanine, caused loss of binding to B70 but not to CD80. These results show that, although the same overall region on CD28 may be involved in the interactions with CD80 and B70, subtle but important differences distinguish recognition by the two molecules. These finding, along with previous observations on the differential pattern of expression and tissue distribution of CD80 and B70, support the contention that these molecules play distinct roles in the regulation of immune responses in vivo.
authors.affiliation: SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406, USA.
authors.forename: A
authors.initials: A
authors.lastname: Truneh
authors.forename: M
authors.initials: M
authors.lastname: Reddy
authors.forename: P
authors.initials: P
authors.lastname: Ryan
authors.forename: S D
authors.initials: SD
authors.lastname: Lyn
authors.forename: C
authors.initials: C
authors.lastname: Eichman
authors.forename: D
authors.initials: D
authors.lastname: Couez
authors.forename: M R
authors.initials: MR
authors.lastname: Hurle
authors.forename: R P
authors.initials: RP
authors.lastname: Sekaly
authors.forename: D
authors.initials: D
authors.lastname: Olive
authors.forename: R
authors.initials: R
authors.lastname: Sweet
mesh_terms: D000069594:Abatacept; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics*; D000943:Antigens, Differentiation / Q000737:chemistry / Q000235:genetics; D018122:B7-1 Antigen / Q000737:chemistry / Q000235:genetics*; D051940:B7-2 Antigen; D001483:Base Sequence; D001666:Binding Sites, Antibody; D018106:CD28 Antigens / Q000737:chemistry / Q000235:genetics*; D060908:CTLA-4 Antigen; D002448:Cell Adhesion / Q000276:immunology; D018604:Epitope Mapping; D005434:Flow Cytometry; D005822:Genetic Vectors; D006801:Humans; D018796:Immunoconjugates; D007135:Immunoglobulin Variable Region / Q000737:chemistry / Q000235:genetics; D007739:L Cells; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed / Q000276:immunology*; D017510:Protein Folding; D016415:Sequence Alignment
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D051940:B7-2 Antigen; D018106:CD28 Antigens; C497964:CD86 protein, human; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; C497965:Cd86 protein, mouse; C556707:Ctla4 protein, mouse; D018796:Immunoconjugates; D007135:Immunoglobulin Variable Region; D008562:Membrane Glycoproteins; D000069594:Abatacept