DOWN-REGULATION OF CHEMOTAXIS OF POLYMORPHONUCLEAR LEUKOCYTES FOLLOWING THERMAL-INJURY INVOLVES 2 DISTINCT MECHANISMS

Thermal injury induces a depression of major effector functions of polymorphonuclear leukocytes (PMNL) that contributes to the increased susceptibility to bacterial infection associated with severe injury. In a study on chemotactic alterations in PMNL induced by thermal injury in a well-characterized guinea pig model, a concomitant reduction in the chemotactic response of PMNL to zymosan-activated serum (ZAS) and FMLP was seen early after thermal injury in temporal association with the previously reported bactericidal defect and depression of superoxide anion production. Unlike the bactericidal defect, the chemotactic alterations were not directly linked to the marked elevation of intracellular cAMP in PMNL associated with thermal injury. Two mechanisms (adaptation and desensitization)were shown to be involved in the reduction of chemotactic responses of PMNL to FMLP and ZAS, respectively. Adaptation appears to be a protective response of PMNL to thermal injury unassociated with receptor down-regulation.