title: Evidence for dimers of MHC class II molecules in B lymphocytes and their role in low affinity T cell responses.
abstract: The crystallographic structure of the MHC class II molecule showed that the alpha beta heterodimer can itself dimerize to form a four chain (alpha beta)2 complex of 120 kDa. Here we provide evidence for the existence of a 120 kDa (alpha beta)2 complex of the class II I-Ek molecules in mouse B cells. Both a 60 kDa and a 120 kDa form of I-Ek are detected by Western blotting and by immunoprecipitation under conditions in which class II alpha beta heterodimers are stable. The 120 kDa I-Ek complex does not contain Ii and, upon warming, dissociates into free alpha and beta chains. The 120 kDa I-Ek complex is expressed at the cell surface, is active in antigen presentation, and appears to play a significant role in T cell responses to low affinity but not to high affinity antigens, possibly by facilitating cross-linking of the T cell receptors.
authors.affiliation: Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: P H
authors.initials: PH
authors.lastname: Schafer
authors.forename: S K
authors.initials: SK
authors.lastname: Pierce
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D017951:Antigen Presentation; D000944:Antigens, Differentiation, B-Lymphocyte; D001402:B-Lymphocytes / Q000378:metabolism* / Q000648:ultrastructure; D015153:Blotting, Western; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D000949:Histocompatibility Antigens Class II / Q000378:metabolism / Q000502:physiology*; D008213:Lymphocyte Activation; D051379:Mice; D011233:Precipitin Tests; D011487:Protein Conformation; D013154:Spleen / Q000737:chemistry; D013601:T-Lymphocytes / Q000276:immunology; D013997:Time Factors
chemical_list: D000911:Antibodies, Monoclonal; D000944:Antigens, Differentiation, B-Lymphocyte; D000949:Histocompatibility Antigens Class II; C024138:I-E-antigen; C045084:invariant chain