title: Receptors for toxic shock syndrome toxin-1 and staphylococcal enterotoxin A on human blood monocytes.
abstract: Staphylococcal toxic shock syndrome toxin-1 (TSST-1) as well as staphylococcal enterotoxin A (SEA) and B (SEB) have recently been shown to bind directly to the class II major histocompatibility antigen, HLA-DR. Whereas others have characterized TSST-1 and SEA binding to HLA-DR on transfected L cells or B lymphoma cell lines, we sought evidence for direct binding of TSST-1 and SEA to HLA-DR on purified human monocytes. A single class of high-affinity receptors was found for both TSST-1 (dissociation constant (Kd) 40 nM, 3.4 x 10(4) receptors per cell) and SEA (Kd 12 nM, 3.2 x 10(4) receptors per cell) on normal human monocytes. Affinity cross-linking of 125I-labeled toxins to monocytes revealed the presence of two membrane protein subunits with molecular masses consistent with the alpha and beta chains of human HLA-DR (35 and 28 kDa, respectively). The anti-HLA-DR monoclonal antibody L243, but not L203 or 2.06, inhibited radiolabeled toxin binding to human monocytes and neutralized the mitogenic response of human T lymphocytes to both toxins. However, L243 was consistently more effective in blocking radiolabeled TSST-1 than SEA binding to human monocytes from the same donors, suggesting that TSST-1 and SEA may be binding to overlapping epitopes rather than to the same epitope on HLA-DR. Because TSST-1 and SEB bind to distinct epitopes on HLA-DR and because SEA cross competes with both TSST-1 and SEB on the HLA-DR receptor, we postulate that SEA occupies a binding site within HLA-DR that overlaps both TSST-1 and SEB.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000328:Adult; D001427:Bacterial Toxins; D004591:Electrophoresis, Polyacrylamide Gel; D004768:Enterotoxins / Q000276:immunology / Q000378:metabolism*; D000939:Epitopes; D006162:Guanylate Cyclase; D006684:HLA-DR Antigens / Q000276:immunology / Q000378:metabolism; D006801:Humans; D009000:Monocytes / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000276:immunology / Q000378:metabolism*; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D018000:Receptors, Peptide; D013211:Staphylococcus aureus / Q000276:immunology / Q000378:metabolism*; D018089:Superantigens
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D000939:Epitopes; D006684:HLA-DR Antigens; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; D018089:Superantigens; C030107:enterotoxin F, Staphylococcal; C026066:enterotoxin A, Staphylococcal; D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled