Carbohydrate- and CD18-dependent neutrophil adhesion to cardiac myocytes: Effects of adenosine

Objective: Adenosine inhibits neutrophil adhesion and injury to isolated cardiac myocytes. In the present study, the contribution of selectin and CD18 interactions to neutrophil-myocyte adhesion and their sensitivity to adenosine were assessed. Methods: Activated human neutrophils and canine myocytes were incubated with inhibitors of CD18 or selectin binding, adenosine, or combinations of both for 30-50 min at 37 degrees C. Neutrophils were pretreated with 0.1 mu M fMLP for 10 min to study L-selectin-independent adhesion. Adhesion was measured by phase contrast microscopy. Results: Anti-L-selectin mAb and the selectin-blocking carbohydrates sialyl Lewis(x) or mannose-6-phosphate as well as anti-CD18 or anti-ICAM-1 mAbs, inhibited cell adhesion (by 84-99% P < 0.05). CD11a, but not CD11b, was responsible fur most of the CD18-mediated binding. An L-selectin-independent interaction between neutrophils and cardiac myocytes was observed that was delayed (peak adhesion al 40-50 min, rather than 30 min), but still inhibited by anti-CD18 mAb (by 65 +/- 11% P < 0.05) and carbohydrates (by 87-97%, each P < 0.05), Adenosine (100 nM) inhibited this late CD18-dependent/L-selectin-independent phase of adhesion (by 61 +/- 14% P < 0.05). The combination of adenosine and anti-CD18 mAb was additive such that adhesion was completely blocked (P < 0.05, compared to either agent alone). Inhibition of adhesion by adenosine was prevented by the A(2) antagonist, DMPX (100 nM), and mimicked by the A(2) agonist, CGS-21680 (10 nM) or the adenosine regulating agents, acadesine (100 mu M) or GP531 (10 mu M). Conclusion: Neutrophil-myocyte adhesion involved both L-selectin-dependent and L-selectin-independent carbohydrate binding as well as CD11a/CD18. Inhibition of adhesion by adenosine interferes with L-selectin-independent carbohydrate binding and possibly CD18.