Adhesion molecules, including integrins, play an important role in the selective recruitment of eosinophils. It has recently been shown that integrins also modulate the functions of eosinophils. Here, we tested the hypothesis that cross-linking of the beta2 integrin, alphaMbeta2Mac-/, leads to intracellular signaling events such as activation of protein tyrosine kinases leading to eosinophil degranulation. Cross-of cell surface CD11b/with anti-tibody and goat anti-G immobilized onto the plate triggered tyrosine phosphorylation of several intracellular proteins, including the one with a 115-kD mass (pp115). The same stimulus also provoked degranulation of eosinophils. These findings suggest that engagement of beta2 integrin on eosinophils triggers the activation of intracellular signaling cascade which leads to cellular degranulation.