Chemiluminescent responses of alveolar macrophages from normal and Mycobacterium bovis BCG-vaccinated rabbits as a function of age

Luminol-dependent chemiluminescence (CL) responses of alveolar macrophages (AM) from normal and Mycobacterium bovis BCG-vaccinated infant and adult rabbits were compared. AM from 1-, 7-, and 14-day-old normal rabbits exhibited much lower peak CL responses than did AM from 28- and 42-day-old normal animals as well as rabbits 2 to 3 or 5 to 6 months and 1 to 2 years of age. The most striking differences among AM from infant and adult rabbits were noted when AM were obtained from 28-day-old and 5- to 6-month old rabbits 21 days after the rabbits were immunized with 200 micrograms of BCG intravenously. In this case, AM from 5- to 6-month-old animals gave peak counts per minute of 400,000 to 500,000 whereas AM from 28-day-old rabbits vaccinated with BCG (harvested at 49 days of age) gave peak counts per minute of only 40,715 +/- 2,688. These data reveal that AM from neonatal animals are grossly deficient as responders to phorbol myristate acetate-induced CL. This deficiency, which improved with age, is still apparent in AM from 28-day-old animals. The data also reveal that BCG vaccination of 28-day-old animals yields AM that are poor responders to phorbol myristate acetate compared with AM from BCG-vaccinated animals 2 to 3 and 5 to 6 months of age. AM from animals vaccinated with BCG at 28 days of age contained fewer and smaller electron-dense lysosomelike structures than did AM from adult rabbits similarly vaccinated. These findings provide an explanation for the difficulties infants have in developing effective cell-mediated immune responses against intracellular parasites.