Mycobacterium lepraemurium infection of nude athymic (nu/nu) mice.

Nude athymic (nu/nu) mice on a BALB/c background and their heterozygous euthymic litter mates (nu/+) were infected with either 10(8) or 10(6) Mycobacterium lepraemurium organisms intravenously or in the left hind footpad (LHF). After LHF infection with 10(8) M. lepraemurium organisms, nu/+ mice slowly developed a response that consisted of LHF swelling and local resistance to Listeria monocytogenes. The lower inoculum induced a proportionately lower response in nu/+ mice, but the nu/nu mice developed neither LHF swelling nor resistance to L. monocytogenes in response to either dose of M. lepraemurium. Counts of M. lepraemurium in the LHF revealed no difference between the nu/+ mice and nu/nu mice. After intravenous infection the nu/+ mice developed splenomegaly, but did not otherwise differ from nu/nu mice with respect to resistance to intravenous challenge with L. monocytogenes or growth of M. lepraemurium in the spleen. In light of the poor responsiveness of nu/+ mice in this experiment, they were then compared with CB6 and B6D2 mice, which are genetically susceptible and resistant to M. lepraemurium, respectively. These mice were infected with either 10(8) or 10(6) M. lepraemurium cells or 10(6) Mycobacterium bovis BCG cells in the LHF. Once again the nu/+ mice responded poorly to M. lepraemurium, the CB6 mice responded very strongly, and the B6D2 mice gave an intermediate response with respect to LHF swelling and resistance to L. monocytogenes. However, M. lepraemurium grew to higher numbers in the LHF of nu/+ and CB6 mice than in B6D2 mice, revealing, in CB6 mice, a dissociation between resistance to L. monocytogenes and M. lepraemurium. All three mouse strains responded strongly to M. bovis BCG, but there was a suggestion that nu/+ mice might be more susceptible to this agent than the other two strains. I concluded that the failure of nu/+ mice to restrict the growth of M. lepraemurium more than nu/nu mice was due to the intrinsic genetic susceptibility of both types of mice. In effect, the nu/+ mice behaved like nu/nu mice, as if they too were deficient in T lymphocytes that were responsive to M. lepraemurium.