AGE-DEPENDENT NEUTROPHIL AND BLOOD-FLOW RESPONSIVENESS IN ACUTE PULMONARY INFLAMMATION IN RABBITS

Diminished ability of neonatal neutrophils to orient and move in a che motactic gradient has been linked to compromised pulmonary host defens e. We investigated whether deficiency of neonatal neutrophil function in vitro was evident in acute pulmonary inflammation. Analysis of neut rophils in vitro showed impaired chemotaxis in 4-wk-old compared with adult rabbits. In vivo-directed migration of labeled neutrophils into the alveolar space of adult rabbits in response to C5f instillation wa s significantly less for neutrophils donated from 4-wk-old rabbits com pared with those from adults. In contrast, there were no differences i n the alveolar accumulation of 4-wk-old and adult labeled neutrophils in 4-wk-old rabbits in response to C5f instillation, although the resp onse showed a shorter time course than seen in adult rabbits. Adult ra bbits diverted 46% of the blood away from the right cranial lung lobe, whereas 4-wk-old rabbits showed no change in blood flow after C5f ins tillation. Megakaryocytes (a source of blood flow mediators) were 3.2- fold greater in adult compared with 4-wk-old lung. These data suggest that the lack. of blood flow diversion from inflamed neonatal lung inc reases neutrophil migration into alveoli, allowing for preservation of an inflammatory response despite neutrophil deficiencies in chemotaxi s.