The deficient migration in vitro of lung macrophages from newborn rats normalizes after three days of maturation in situ.

Because there are functional deficiencies in neonatal phagocytes, we investigated age-dependent differences in the directed migration of rat pulmonary macrophages (PM). Directed migration of PMs from newborn (less than 24 h old) rats towards partially purified rat C5a was lower than that of PMs from adults, but reached adult levels by the third post-natal day. Calculation of the dose of C5a resulting in a half-maximal migratory response (ED-50) revealed that the ED-50s for all age groups studied were similar. These results suggest that responding PMs at all times after birth have comparable sensitivity to C5a, but that a lower percentage of newborn PMs migrate toward this factor because of defects in either signal transduction or cell motility.