title: Mechanism of Staphylococcus aureus exotoxin A inhibition of Ig production by human B cells.
abstract: Staphylococcus enterotoxins and toxic shock syndrome toxin 1 are members of a family of exoproteins that are produced by staphylococci and bind specifically to MHC class II molecules. Upon binding to MHC class II molecules, these exoproteins are potent stimulators of T cell proliferation via interaction with specific TCR V-beta segments of both CD4+ and CD8+ T cells. These exoproteins also directly stimulate monocytes to secrete IL-1 and TNF-alpha. Furthermore, these exoproteins have a profound inhibitory effect on Ig production by PBMC. We examined the effects of Staphylococcus enterotoxin A (SEA) on proliferation and Ig production of highly purified human B cells. Our results demonstrated that the binding of SEA to MHC class II molecules on B cells does not alter their ability to proliferate in response to Staphylococcus aureus Cowan strain I (SAC) or to produce Ig in response to SAC plus rIL-2. In contrast, the anti-DR mAb L243 inhibited both B cell proliferation and Ig production. Unable to determine a direct effect of SEA on B cell function, we investigated whether the capacity of SEA to inhibit SAC-induced Ig production by PBMC was T cell-dependent. Our results demonstrated that in the presence of T cells, under appropriate conditions, SEA can either function as a nominal Ag for stimulation of B cell proliferation and Ig production or induce T cell-mediated suppression of Ig production. SEA-induced Ig production required T cell help, which was dependent on pretreatment of the T cells with irradiation or mitomycin C; Ig production was not induced by SEA in the absence of T cells or in the presence of untreated T cells. Furthermore, SEA inhibited Ig production in SAC-stimulated cultures of autologous B cells and untreated T cells; pretreatment of the T cells with irradiation or mitomycin C abrogated SEA-induced inhibition of Ig production. Thus, T cell suppression of SAC-induced Ig production was dependent on T cell proliferation. Similar results were observed with both SEA and toxic shock syndrome toxin 1.
authors.affiliation: Department of Medicine, Baylor College of Medicine, Houston, TX.
authors.forename: A B
authors.initials: AB
authors.lastname: Moseley
authors.forename: D P
authors.initials: DP
authors.lastname: Huston
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D001402:B-Lymphocytes / Q000187:drug effects* / Q000276:immunology; D001427:Bacterial Toxins; D001665:Binding Sites; D004768:Enterotoxins / Q000494:pharmacology*; D005098:Exotoxins / Q000494:pharmacology*; D006684:HLA-DR Antigens / Q000276:immunology; D006801:Humans; D007136:Immunoglobulins / Q000096:biosynthesis*; D008213:Lymphocyte Activation; D015375:Receptors, Interleukin-2 / Q000032:analysis; D013211:Staphylococcus aureus / Q000378:metabolism*; D018089:Superantigens; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D001427:Bacterial Toxins; D004768:Enterotoxins; D005098:Exotoxins; D006684:HLA-DR Antigens; D007136:Immunoglobulins; D015375:Receptors, Interleukin-2; D018089:Superantigens; C030107:enterotoxin F, Staphylococcal; C026066:enterotoxin A, Staphylococcal