title: Microvilli structures on B lymphocytes: inducible functional domains?
abstract: Interactive contact between B lymphocytes and T cells is necessary for their expansion during an immune response. It has been shown that B lymphocytes receive signals from T cells, such as IL-4 and cross-linking of CD40, which are crucial for their differentiation. We previously found that these factors induce formation of microvilli on B cells and that this was correlated with increased homotypic adhesion of B lymphocytes. In this study we have investigated if IL-4 induce segregation of proteins to microvilli and lipid rafts. Using immuno-electron microscopy we analyzed cell-surface distribution of molecules involved in B-T cell co-activation. Recruitment to detergent-resistant membrane fractions was analyzed using sucrose gradient centrifugation. We found that microvilli were enriched in ICAM-1 and MHC class II molecules. In contrast, LFA-1 and CD40 were more abundant on the smooth cell surfaces, while B7-2 (CD86) was randomly distributed. We also discovered that depletion of cholesterol, using beta-methyl-cyclodextrin, lowered the number of microvilli, indicating that intact lipid rafts are required for their expression. Moreover, activation of B lymphocytes by lipopolysaccharide (LPS) induced increased expression of GM(1), a marker for lipid rafts. However, although both surface and total levels of GM(1) were similar in B lymphocytes stimulated with either LPS or LPS plus IL-4, GM(1) was mainly expressed on microvilli in LPS plus IL-4-stimulated cells. Taken together, our results indicate that microvilli represent distinct inducible membrane domains that can regulate direct cell-cell interactions via grouping and three-dimensional presentation of cell-surface receptors.
authors.affiliation: Department of Cell and Molecular Biology, Karolinska Institutet, 17177 Stockholm, Sweden.
authors.forename: Gediminas
authors.initials: G
authors.lastname: Greicius
authors.forename: Lisa
authors.initials: L
authors.lastname: Westerberg
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Davey
authors.forename: Eva
authors.initials: E
authors.lastname: Buentke
authors.forename: Annika
authors.initials: A
authors.lastname: Scheynius
authors.forename: Johan
authors.initials: J
authors.lastname: Thyberg
authors.forename: Eva
authors.initials: E
authors.lastname: Severinson
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D001402:B-Lymphocytes / Q000276:immunology / Q000648:ultrastructure*; D051940:B7-2 Antigen; D019013:CD40 Antigens / Q000378:metabolism; D002450:Cell Communication / Q000187:drug effects / Q000502:physiology; D002772:Cholera Toxin / Q000494:pharmacology; D003505:Cyclodextrins / Q000494:pharmacology; D005802:Genes, MHC Class II / Q000502:physiology*; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism*; D015847:Interleukin-4 / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism / Q000648:ultrastructure*; D051379:Mice; D008871:Microvilli / Q000276:immunology / Q000648:ultrastructure*; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D015703:Antigens, CD; D051940:B7-2 Antigen; D019013:CD40 Antigens; C497965:Cd86 protein, mouse; D003505:Cyclodextrins; D008070:Lipopolysaccharides; D016169:Lymphocyte Function-Associated Antigen-1; D008562:Membrane Glycoproteins; D018799:Intercellular Adhesion Molecule-1; D015847:Interleukin-4; D002772:Cholera Toxin