Activation of human basophils byStaphylococcus aureus Cowan I. II. Alternative F(ab′)-mediated mechanism

Abstract

We investigated the capacity ofStaphylococcus aureus Cowan I (Cowan Staph A⁺) andStaphylococcus aureus Wood 46 (Wood Staph A⁻) to induce histamine release from human basophilsin vitro. Cowan Staph A⁺ (3 × 10⁶ to 3 × 10⁸/ml), which synthesizes protein A (Staph A), stimulated the release of histamine from basophils, whereas Wood Staph A⁻ (3×10⁶ to 3×10⁹/ml), which does not synthesize Staph A, did not induce histamine secretion. Soluble Staph A (10⁻³ to 10 μg/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 Fe-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.