PLASMA ACTIVATION OF NEUTROPHIL CD18 AFTER SKELETAL-MUSCLE ISCHEMIA -A POTENTIAL MECHANISM FOR LATE SYSTEMIC INJURY

Reperfusion of acutely ischemic skeletal muscle is associated with neu trophil activation, which may augment local injury or cause damage to distant organs. Polymorphonuclear neutrophil glycoprotein CD18 plays a role in this injury, since its blockade substantially reduces damage; however, its mechanisms of control during reperfusion are poorly unde rstood. The purpose of this study was to investigate the importance of circulating plasma factors to CD18-dependent neutrophil function duri ng reperfusion and to relate these to quantitative expression of CD18. Eight rabbits were subjected to hindlimb ischemia for 5 h, followed b y 48 h of reperfusion. Plasma collected at seven intervals was incubat ed with unstimulated neutrophils from uninjured rabbits. CD18-specific neutrophil activation was evaluated by quantifying adherence to prote in-coated polystyrene and by measuring oxidant production, detected by chemiluminescence after exposure to complement-opsonized zymosan. CD1 8 was quantified cytofluorometrically. Plasma collected at end ischemi a and during early reperfusion affected no significant alterations of adhesion, oxidant production, or CD18. Late reperfusion plasma (betwee n 8 and 48 h) significantly increased adherence and oxidant production (to 4.11 +/- 0.61 and 2.60 +/- 0.32 times the values of preischemic p lasma, P < 0.006). Peak adherence, oxidant production, and CD18 expres sion were evoked synchronously by 24 h plasma. CD18 expression increas ed only at 24 h and did not increase proportional to increases in adhe rence and oxidant production. Control plasma (nonischemic, n = 5) elic ited no significant differences of any inflammatory measure during sha m ischemia or reperfusion. These results indicate that endogenous medi ators may evoke a progressive systemic inflammatory response after isc hemia by stimulating CD18-dependent neutrophil function in a delayed b ut prolonged manner.