title: Cholera toxin B subunit binding to an antigen-presenting cell directly co-stimulates cytokine production from a T cell clone.
abstract: Cholera toxin (CT) is a powerful immunomodulator with strong adjuvant activity. Much of this activity is retained by the binding component alone, cholera toxin B subunit (CTB). Little is known about the mechanism of the immunomodulatory activity of CTB. In this study, both CT and CTB were found to dramatically enhance IL-4 production from a T cell clone stimulated with antigen and the B cell hybridoma LB as antigen-presenting cell (APC). Enhancement of cytokine production was seen following pretreatment of the APC with CT or CTB, while pretreatment of the T cells had no effect. Furthermore, stimulatory activity on the APC was stable to fixation with paraformaldehyde, demonstrating that the activity was mediated by a surface molecule on the APC. CT-pretreated APC also enhanced IL-4 production from anti-CD3 mAb-stimulated T cells, indicating that CT was providing a co-stimulatory signal. CT treatment of LB cells did not alter the expression of class II MHC molecules, CTLA-4 counter-receptors, LFA-1 or ICAM-1. When mAb were raised against the CT-pretreated APC, the only antibodies that were found to inhibit IL-4 production were those specific for CTB itself. The antibodies blocked even when the CT or CTB were already bound to the APC, arguing that co-stimulation was provided by a direct interaction with CTB. Blocking experiments suggested that APC-associated CTB molecules are interacting with non-GM1 receptors on the T cells. This novel finding of CTB-mediated T-B interaction provides one of the first potential mechanisms for the adjuvant activity of CTB.
authors.affiliation: Department of Biological Chemistry, University of Maryland at Baltimore 21201, USA.
authors.forename: T K
authors.initials: TK
authors.lastname: Li
authors.forename: B S
authors.initials: BS
authors.lastname: Fox
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000938:Antigen-Presenting Cells / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism*; D017252:CD3 Complex / Q000276:immunology; D002772:Cholera Toxin / Q000276:immunology / Q000378:metabolism* / Q000494:pharmacology*; D002999:Clone Cells; D016207:Cytokines / Q000096:biosynthesis* / Q000187:drug effects; D015847:Interleukin-4 / Q000096:biosynthesis; D008213:Lymphocyte Activation / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D011485:Protein Binding / Q000276:immunology; D051381:Rats; D011917:Rats, Inbred Lew; D018418:Th2 Cells / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D017252:CD3 Complex; D016207:Cytokines; D015847:Interleukin-4; D002772:Cholera Toxin