Low responsiveness to MLM bacilli associated with an impaired macrophage function in CBA/J mice

It has previously been reported that susceptibility to Mycobacterium lepraemurium (MLM) infection (subcutaneous inoculation) differs markedly between CBA/J and C57BL/6 mice. The high susceptibility of CBA/J mice was shown to be due to the generation of cyclophosphamide-sensitive, I-Jk-positive suppressor T cells. In the present study, we attempt to show functional differences between splenic macrophages of both strains of mice in terms of their phagocytic and antigen-presenting activities against MLM bacilli. The results show that (a) the secondary MLM-induced T-cell proliferative response is dependent on Ia-positive antigen-presenting cells (APC), (b) macrophages of CBA/J mice are able to present antigens to F1 T cells, and yet (c) they show an extremely low phagocytic activity, (d) antigen presentation by APC of CBA/J mice lasted for a longer period than that of C57BL/6 mice after MLM infection. These results suggest that there is a functional difference in CBA/J and C57BL/6 APC, which could account for the phenotypic difference in immune responsiveness to MLM bacilli.