Immune responsiveness in Mycobacterium avium-infected mice: changes in the proportion of T cell subsets and antibody production during the course of infection

Abstract

SUMMARY The C57B1/6 susceptible (BegS) and its resistant (Begr) congenic mouse, previously developed by retrogressive backcrossing, were infected with 1 × 106 colony-forming units (CFU) of Mycobacterium avium and bacterial growth and their immune responses during the early and prolonged periods of infection were examined. There was a high proliferation in the liver and spleen of BegS mice, whereas no proliferation was observed in the Begr mice. Similarly, the sizes and weights of these organs were much higher than those of their Begr counterparts. The size and number of granulomas in Begr were also found to be higher than those of Begr. The CD3+ and CD4+ subsets increased dramatically in both mice during the early stage of infection. However, in the later phase of the infection, these populations decreased dramatically in Begr mice, but not in Begr mice, resulting in a depression in cell-mediated immune responses. No significant decrease in cellmediated immune responses was observed in Begr mice even after prolonged infection. ELISA was performed to determine the antibody levels in both mice, and it was found that serum IgG and IgM levels in Begs were comparatively higher than those in Begr mice throughout the period of infection. The Beg gene therefore may have an important role in the maintenance of resistance not only in the early phase but also in the later phase of Myco. avium infection.