Activation of human basophils by Staphylococcus aureus Cowan I. II. Alternative F(ab')-mediated mechanism

We investigated the capacity of Staphylococcus aureus Cowan I (Cowan Staph A+) and Staphylococcus aureus Wood 46 (Wood Staph A-) to induce histamine release from human basophils in vitro. Cowan Staph A+ (3 X 10(6) to 3 X 10(8)/ml), which synthesizes protein A (Staph A), stimulated the release of histamine from basophils, whereas Wood Staph A- (3 X 10(6) to 3 X 10(9)/ml), which does not synthesize Staph A, did not induce histamine secretion. Soluble Staph A (10(-3) to 10 micrograms/ml) also induced histamine secretion from human basophils, Hyperiodination of Staph A, which destroys over 90% of the original Fc reactivity without altering the Fab binding site, did not alter this protein's ability to induce histamine release. The stimulating effect of Staph A was suppressed by preincubation with human polyclonal IgG and a human monoclonal IgM, which have F(ab')-Staph A reactivity. In contrast, rabbit IgG and a human monoclonal IgM possessing only Fc-Staph A reactivity did not inhibit Staph A activity. Preincubation with Staph A or Cowan Staph A+ resulted in complete cross-desensitization to a subsequent challenge with homologous and heterologous stimuli. These results indicate that Staph A and Cowan Staph A+ activate human basophils by interacting with the F(ab')2 region of IgE and/or IgG present on the cell surface.