Susceptibility of 'et,' the spontaneously mutating CD1-derived nude mouse, to infection of M. lepraemurium

We have studied the susceptibility to infection by Mycobacterium lepraemurium (MLM) of a nude, hypothymic, CD1-derived, spontaneous mouse mutant called 'et' because of its extraterrestrial appearance. We found that despite their hypothymia, et/et mice were not more susceptible to infection by MLM than their euthymic et/+ counterparts. Infection of both et/et and et/+ mice with 50 x 10⁶ bacilli by the intraperitoneal route led only to a mild infection with low levels of antimycobacterial antibodies and a small number of lesions. These lesions were indicative of reactive hepatitis and hyaline perisplenitis with lymphoid hyperplasia. Some small bacilliferous granulomas were also observed at the end of the experiment (5 months of infection). CD1 mice behave in a rather 'resistant' manner to the infection by MLM. It is clear that the nu gene is not necessarily linked to the thymus defect, and it is also clear that the hypothymia of et/et mice does not obviously affect their general cell-mediated immune competence.