Impaired actin polymerization and depolymerization in neutrophils from patients with thermal injury

Acquired neutrophil dysfunction is considered an important cause of increased susceptibility to infection in patients with burns. In the early postinjury phase, large amounts of circulating chemoattractants, cytokines and endotoxins induce strong systemic activation of neutrophils which may impair their motile functions. Actin is the most prevalent component of the microfilament lattice that generates force for the neutrophil motile responses, and in the present study we examined the dynamics of actin polymerization and depolymerization in neutrophils from 11 patients with large burns. At admission, the amount of polymerized actin in unstimulated neutrophils was 39.9 per cent higher than that of parallel controls. In addition, there was a positive correlation between the amount of polymerized actin and the total body surface area (TBSA) burn. The time course of patient neutrophil actin polymerization in response to FMLP, C5a, (Ser-IL-8) 72, (Ala-IL-8) 77 and crosslinking of surface FcγRII was similar to that of controls, and the maximal amount of neutrophil F-actin was demonstrated after 30 s stimulation. At the peak of actin polymerization, however, patient neutrophils contained 27.3, 24.0, 24.7 and 25.6 per cent more polymerized actin than control cells stimulated with FMLP, (Ser-IL,-8) 72, (Ala-8) 77 and FcγRII crosslinking, respectively. However, the relative increase of neutrophil F-actin following stimulation was significantly lower in patients than in controls. Moreover, the rate of patient neutrophil actin depolymerization was 39.0, 23.5, 63.3 and 51.7 per cent lower than that of controls after stimulation with FMLP, C5a (Ser-IL-8) 72 and FcγRII crosslinking, respectively. At discharge, the dynamics of neutrophil actin polymerization and depolymerization were similar to that of controls. The results demonstrate that in neutrophils during the early postburn phase, there are increased basal levels of polymerized actin, a lower responsiveness to stimulation and a reduced rate of actin depolymerization. As periodic polymerization and depolymerization of actin is essential for all neutrophil motile responses, it is probable that the alterations observed may contribute significantly to the overall neutrophil dysfunction following thermal injury.