Characteristics of Immunosuppressive Macrophages Induced in Host Spleen Cells by Mycobacterium avium Complex and Mycobacterium tuberculosis Infections in Mice

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Abstract
The profile of generation and characteristics of immunosuppressive macrophages (M.vphi.s), which suppress the ConA-mitogenic response of spleen cells (SPCs), in host CBA/JN mice during the course of Mycobacterium avium complex (MAC) and M. tuberculosis (MT) infections were investigated. In both infections, a marked reduction in ConA mitogenic response of splenic T cells was seen around 2 weeks after infection, and this was accompanied by generation of potent immunosuppressive M.vphi.s in the SPCs of infected mice. The suppressive activity was much stronger in MT-infected mice than in MAC-infected ones. In both infections, the large part of the suppressive M.vphi.s exhibited suppressor activity that depended on the arachidonic acid cascade, particularly mediated by prostaglandin (PGs), and the remainder showed the suppressor action independent from PGs. The unique finding of this study is that the generation of IL-2 reactive T cell populations in SPCs in response to ConA signal was markedly inhibited by the MAC- and MT-induced immunosuppressive M.vphi.s, whereas the suppressive M.vphi.s failed to reduce the IL-2-producing ability of splenic T cells. In any case, the present results indicate a close similarity in immunosuppressive M.vphi.s induced by MAC and MT infections.