title: Activated T cells induce expression of B7/BB1 on normal or leukemic B cells through a CD40-dependent signal.
abstract: Cognate interactions between antigen-presenting B and T cells play crucial roles in immunologic responses. T cells that have been activated via the crosslinking of CD3 are able to induce B cell proliferation and immunoglobulin secretion in a major histocompatibility complex-unrestricted and contact-dependent manner. We find that such activated human CD4+ T cells, but not control Ig-treated T cells, may induce normal or leukemic B cells to express B7/BB1 and significantly higher levels of CD54 intercellular adhesion molecule 1 via a process that also requires direct cell-cell contact. To discern what cell surface molecule(s) may be responsible for signalling B cells to express B7/BB1, we added various monoclonal antibodies (mAbs) specific for T or B cell accessory molecules or control mAbs to cocultures of alpha-CD3-activated T cells and resting B cells. We find that only alpha-CD40 mAbs can significantly inhibit the increased expression of B7/BB1, suggesting that the ligand for CD40 expressed on activated T cells may be an important inducer of B7/BB1 expression. Subsequent experiments in fact demonstrate that alpha-CD40 mAbs, but not control mAbs, induce changes in B cell phenotype similar to those induced by activated T cells when the mAbs are presented on Fc gamma RII (CDw32)-expressing L cells. These phenotypic changes have significant effects on B cell function. Whereas chronic lymphocytic leukemia (CLL) B cells normally are very poor stimulators in allogeneic mixed lymphocyte reactions (MLRs), CLL-B cells preactivated via CD40 crosslinking are significantly better presenters of alloantigen, affecting up to 30-fold-greater stimulation of T cell proliferation than that induced by control treated or nontreated CLL-B cells. Similarly, the MLR of T cells stimulated by allogeneic nonleukemic B cells can be enhanced significantly if the stimulator B cells are preactivated via CD40 crosslinking. The enhanced MLR generated by such preactivated B cells may be inhibited by blocking B7/BB1-CD28 interaction with CTLA4Ig. These studies demonstrate a novel, CD40-dependent pathway for inducing B cell expression of B7/BB1 and enhancing B cell antigen-presenting cell activity that can be initiated via cell-cell contact with alpha-CD3-stimulated CD4+ T cells.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla 92093-0663.
authors.forename: E A
authors.initials: EA
authors.lastname: Ranheim
authors.forename: T J
authors.initials: TJ
authors.lastname: Kipps
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000276:immunology*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000276:immunology*; D000954:Antigens, Surface / Q000096:biosynthesis*; D001402:B-Lymphocytes / Q000276:immunology*; D018122:B7-1 Antigen; D019013:CD40 Antigens; D015815:Cell Adhesion Molecules / Q000096:biosynthesis; D002478:Cells, Cultured; D006801:Humans; D018799:Intercellular Adhesion Molecule-1; D007700:Kinetics; D007938:Leukemia / Q000276:immunology*; D008213:Lymphocyte Activation; D051379:Mice; D010641:Phenotype; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; D000954:Antigens, Surface; D018122:B7-1 Antigen; D019013:CD40 Antigens; D015815:Cell Adhesion Molecules; D018799:Intercellular Adhesion Molecule-1