Eosinophil major basic protein activates human cord blood mast cells primed with fibroblast membranes by integrin‐β1

Background Mast cell ( MC ) – eosinophil ( E os) activating cross‐talk might be critical for the severity and chronicity of allergy. Among soluble mediators, eosinophil major basic protein ( MBP ), a hallmark of allergy, is particularly important because it was shown to activate specific MC subtypes. We previously demonstrated that MBP activates I g E ‐desensitized rat MC and human lung and cord blood‐derived MC ( CBMC ) after priming with fibroblast membranal stem cell factor. However, a distinct mechanism for this activation was missing. Therefore, we aimed to investigate it. Methods Major basic protein‐1 activation of CBMC primed with fibroblast‐derived membranes ( FBM ) was measured by β‐hexosaminidase and tryptase release. Chemical cross‐linking followed by micrometric flow cytometry probed direct interactions. Antibodies neutralized integrin‐β1 and recognized its active form. Pertussis toxin ( P tx) was used to decrease integrin‐β1 active form expression. Hematopoietic cell kinase ( H ck) was identified by immunoprecipitation ( IP ) and silenced by si RNA . Results Major basic protein‐1‐induced CBMC activation is mediated partly by MBP 1–integrin‐β1 interaction on the MC surface. FBM prime CBMC via a G protein, as confirmed by P tx, to shift integrin‐β1 to its active form. Following MBP 1 binding, integrin‐β1 binds H ck that further transduces the activation signal. MC priming with FBM leads to up‐regulation in H ck protein level. MC integrin‐β1 neutralization inhibits MBP 1‐induced activation and uptake. Hck silencing results with reduced MBP 1‐induced activation. Conclusions Fibroblast‐derived membranes, integrin‐β1, and H ck are involved in MBP 1‐induced activation of CBMC and therefore represent a distinct mechanism for this activation. This finding might implicate integrin‐β1 and Hck as targets for decreasing MC – E os activating cross‐talk in allergy.