EMIGRATED RAT NEUTROPHILS ADHERE TO CARDIAC MYOCYTES VIA ALPHA(4) INTEGRIN

Previous work has shown that neutrophils isolated from whole blood adh ere to cardiac myocytes via CD18 (beta(2) integrin) to cause injury to the heart cells. In vitro, we have found that upon endothelial transm igration, neutrophils can also express alpha(4) beta(1); however, whet her this contributes to neutrophil adhesion to parenchymal cells remai ns entirely unknown. Unstimulated and tumor necrosis factor-alpha-stim ulated rat cardiac myocytes adherent to gelatin-coated coverslips supp orted N-formyl-Met-Leu-Phe (fMLP)-induced neutrophil (isolated from wh ole blood) adhesion entirely via CD18 (blocked with monoclonal antibod y [mAb] WT-3). Emigrated neutrophils spontaneously adhered to cardiac myocytes also entirely via CD18. However. if fMLP was used to restimul ate emigrated neutrophils, the adhesion to cardiac myocytes was entire ly independent of CD18. Although an anti-alpha(4) integrin antibody (m Ab TA-2) alone did not reduce the emigrated neutrophilmyocyte interact ion, dual administration of TA-2 and WT-3 reduced adhesion by 81%. alp ha(4) integrin was expressed in small amounts on the surface of circul ating neutrophils, increased following transmigration, and then increa sed >5-fold after restimulation of these emigrated neutrophils, In the presence of the anti-CD18 antibody, a fibronectin fragment (FN-30) bu t not a vascular cell adhesion molecule-1 antibody (mAb 5F10) inhibite d neutrophil-myocyte interactions by 80%. Similar results were seen wh en the rat chemokine CINC-gro was used instead of fMLP, suggesting tha t the alpha 4-dependent adhesion was not specific to fMLP. These data demonstrate that a, integrin can be physiologically induced to increas e in number and avidity after neutrophil emigration and that this adhe sion molecule can cause firm adhesion to fibronectin on parenchymal ce lls, including rat cardiac myocytes.