AN EXPERIMENTAL-MODEL TO DETERMINE THE EFFECT OF IRRADIATED TISSUE ONNEUTROPHIL FUNCTION

Complications of irradiated tissue include infections and impaired hea ling. Although fibrosis and hypovascularity contribute, a cellular mec hanism has not been identified. This study examines the effect of radi ation (10 to 30 Gy) on neutrophil function in a rabbit wound cylinder model. At 3 to 12 weeks after radiation, subcutaneous wound cylinders were implanted in both irradiated and control fields in 19 rabbits. Wo und neutrophils were subsequently assayed for phagocytosis (H-3-labele d Staphylococcus aureus assay), superoxide production (cytochrome c re duction assay), and surface Mac-1 expression (flow cytometric assay us ing MHM 23 monoclonal antibody). Phagocytosis of H-3-labeled S. aureus was significantly lower in neutrophils from irradiated fields compare d with controls at 6 and 12 weeks after radiation (6.5 versus 18.9 bac teria per neutrophil at 12 weeks; p = 0.027). Stimulated neutrophils f rom irradiated tissue could not increase superoxide production or Mac- 1 expression as much as controls, with differences increasing as posti rradiation time increased. The diminished phagocytosis, superoxide pro duction, and Mac-1 expression provide a cellular mechanism that may ac count for susceptibility to infection and poor healing in irradiated t issues.