Role of mononuclear phagocytes in expression of resistance and susceptibility to Mycobacterium avium infections in mice.

The growth of Mycobacterium avium 702 in the spleens and livers of four inbred strains of mice varied such that the mice could be separated into naturally susceptible (BALB/c and C57BL/6) and naturally resistant (A/Tru and DBA/2) strains. This phenomenon was independent of the size of the infecting inoculum of bacteria in that both low (10(4))- and high (10(7))-dose inocula of M. avium grew progressively in susceptible strains and were eliminated from the target organs of resistant strains. Resistance and susceptibility were also demonstrated in in vitro preparations of macrophages from these strains of mice. Over a 7-day period, replication of M. avium in susceptible mouse macrophages was far greater than that in resistant macrophages. Evidence was obtained to suggest that toxic oxygen metabolites were not responsible for this difference. Though no difference was found in the rate of clearance of M. avium from the blood of susceptible or resistant mice, resident macrophages from susceptible mice ingested more M. avium in vitro than did resident macrophages from resistant animals. Growth of M. avium in spleens of susceptible mice induced a large influx of phagocytes, whereas this was not observed in resistant mice. In contrast to this it was found that, after injection of a variety of inflammatory agents, influx of leukocytes into the peritoneal cavity could not be used to distinguish susceptible and resistant strains of mice.