Enhanced recovery of murine alveolar macrophages: morphological and functional characteristics following intravenous injection of heat-killed Mycobacterium bovis BCG.

The kinetics of induction of the bronchoalveolar cell population (i.e., alveolar macrophages [AM], lymphocytes, and polymorphonuclear leukocytes) was studied in mice inoculated intravenously with heat-killed Mycobacterium bovis BCG. Injection of BCG at 100 and 500 micrograms but not at 10 micrograms per mouse resulted in an increase in the total number of bronchoalveolar cells (threefold) and in the number of AM (sixfold) recovered by bronchoalveolar lavage in a time-dependent manner, as compared with control mice. A significant increase in the number of lymphocytes was also observed between days 2 and 4 after injection, but this number returned to normal levels by day 8, whereas the number of polymorphonuclear leukocytes was not significantly altered. AM were characteristically phagocytic and stained positively for nonspecific esterase. AM recruited in response to BCG injection were activated, as indicated by elevated levels of acid phosphatase activity and decreased levels of membrane 5'-nucleotidase activity. However, both resident and BCG-induced AM suppressed the in vitro plaque-forming cell response of sheep erythrocyte-primed mice to the same extent. These results indicate that injection of heat-killed BCG induced increased numbers of activated AM, which appeared to be functionally similar to resident AM in their ability to phagocytize and modulate in vitro immune responses.