We compared the abilities of alveolar macrophages (AM) from neonatal and adult rabbits to generate and release superoxide (O2-) after exposure to soluble and particulate stimuli. Basal rates of O2- release, 0.1-0.2 nmol/10(6)AM/10 min, were modestly increased by exposing AM to phorbol myristate acetate, (dihydro)cytochalasin B, or cytochalasin C. Opsonized zymosan was a more effective stimulus, and maximal rates of O2- release were observed when AM were stimulated by a combination of opsonized zymosan and one of the aforementioned cytochalasins. Cytochalasins D and E were each potent activators of O2- production by AM in the absence of additional stimuli. Adult AM released 24.8 +/- 6.0, 20.4 +/- 4.4, and 33.5 +/- 6.4 nmol O2-/10(6)AM/10 min after stimulation by cytochalasin D, cytochalasin E, and dihydrocytochalasin B plus opsonized zymosan, respectively. Following exposure to the same stimuli, AM from 1, 3- and 7-day-old rabbits released O2- at rates that ranged from 45 to 75% of corresponding adult values. The discrepancy between O2- production by neonatal and adult AM was accentuated when comparisons were restricted to AM recovered from bacteriologically sterile respiratory tracts. Our data show the O2- generating capacity of neonatal AM to be substantially less than that of the adult AM. Immaturity of this response could predispose neonates to pulmonary infection.
Aging Animals