Age-dependent neutrophil and blood flow responsiveness in acute pulmonary inflammation in rabbits

Diminished ability of neonatal neutrophils to orient and move in a chemotactic gradient has been linked to compromised pulmonary host defense. We investigated whether deficiency of neonatal neutrophil function in vitro was evident in acute pulmonary inflammation. Analysis of neutrophils 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 was significantly less for neutrophils donated from 4-wk-old rabbits compared with those from adults. In contrast, there were no differences in the alveolar accumulation of 4-wk-old and adult labeled neutrophils in 4-wk-old rabbits in response to C5f instillation, although the response showed a shorter time course than seen in adult rabbits. Adult rabbits 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 instillation. 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 increases neutrophil migration into alveoli, allowing for preservation of an inflammatory response despite neutrophil deficiencies in chemotaxis.