CARBOHYDRATE-DEPENDENT AND CD18-DEPENDENT NEUTROPHIL ADHESION TO CARDIAC MYOCYTES - EFFECTS OF ADENOSINE

Objective: Adenosine inhibits neutrophil adhesion and injury to isolat ed cardiac myocytes. In the present study, the contribution of selecti n and CD18 interactions to neutrophil-myocyte adhesion and their sensi tivity to adenosine were assessed. Methods: Activated human neutrophil s and canine myocytes were incubated with inhibitors of CD18 or select in binding, adenosine, or combinations of both for 30-50 min at 37 deg rees C. Neutrophils were pretreated with 0.1 mu M fMLP for 10 min to s tudy L-selectin-independent adhesion. Adhesion was measured by phase c ontrast microscopy. Results: Anti-L-selectin mAb and the selectin-bloc king carbohydrates sialyl Lewis(x) or mannose-6-phosphate as well as a nti-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-media ted 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-indep endent phase of adhesion (by 61 +/- 14% P < 0.05). The combination of adenosine and anti-CD18 mAb was additive such that adhesion was comple tely 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 adeno sine regulating agents, acadesine (100 mu M) or GP531 (10 mu M). Concl usion: 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-indepe ndent carbohydrate binding and possibly CD18.