title: Defining the recognition elements of Lewis Y-reactive antibodies.
abstract: Antibody response to carbohydrate antigens is often independent of T cells and the process of affinity/specificity improvement is considered strictly dependent on the germinal centers. Antibodies induced during a T cell-independent type 2 (TI-2) response are less variable and less functionally versatile than those induced with T cell help. The antigen specificity consequences of accumulation of somatic mutations in antibodies during TI-2 responses of Marginal Zone (MZ) B cells is a fact that still needs explanation. Germline genes that define carbohydrate-reactive antibodies are known to sculpt antibody-combining sites containing innate, key side-chain contacts that define the antigen recognition step. However, substitutions associated with MZ B cell derived antibodies might affect the mobility and polyspecificity of the antibody. To examine this hypothesis, we analyzed antibodies reactive with the neolactoseries antigen Lewis Y (LeY) to define the residue subset required for the reactive repertoire for the LeY antigen. Our molecular simulation studies of crystallographically determined and modeled antibody-LeY complexes suggests that the heavy-chain germline gene VH7183.a13.20 and the light-chain Vκ cr1 germline gene are sufficient to account for the recognition of the trisaccharide-H determinant Types 1-4, while the specificity for LeY is driven by the CDR3 backbone conformation of the heavy chain and not the side chain interactions. These results confirm that these monoclonals use germline-encoded amino acids to recognize simple carbohydrate determinants like trisaccharide-H but relies on somatic mutations in the periphery of the combining site to modify affinity for LeY through electrostatic interactions that leads to their optimized binding. These observations bring further attention to the role of mutations in T-cell independent antibodies to distinguish self from non-self carbohydrate antigens.
authors.affiliation: Bioinformatics Graduate Program, University of Arkansas at Little Rock/University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
authors.forename: Somdutta
authors.initials: S
authors.lastname: Saha
authors.affiliation: Stephan Angelov Institute of Microbiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
authors.forename: Anastas
authors.initials: A
authors.lastname: Pashov
authors.affiliation: Winthrop P. Rockefeller Cancer Institute, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Siegel
authors.affiliation: Department of Biological Sciences, Research Division of Immunology, Cedars-Sinai Medical Center, Los Angeles, California, United States of America.
authors.forename: Ramachandran
authors.initials: R
authors.lastname: Murali
authors.affiliation: Winthrop P. Rockefeller Cancer Institute, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kieber-Emmons
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D001666:Binding Sites, Antibody / Q000276:immunology*; D002236:Carbohydrate Conformation; D050440:Immunoglobulin Subunits / Q000737:chemistry / Q000276:immunology; D007983:Lewis Blood Group Antigens / Q000737:chemistry / Q000276:immunology*; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding / Q000276:immunology; D011487:Protein Conformation; D016415:Sequence Alignment
chemical_list: D000906:Antibodies; D000911:Antibodies, Monoclonal; D050440:Immunoglobulin Subunits; D007983:Lewis Blood Group Antigens; C094162:Lewis Y antigen