Paradoxical functions of alveolar macrophages from Calmette-Guérin bacillus-immunized rats

The effect of autologous alveolar macrophages on the lymphoproliferative response to mitogens was investigated using Calmette-Guérin bacillus (BCG)-immunized rats. The proliferation of lymphocytes obtained from normal rats was suppressed when the lymphocytes were cultured with alveolar macrophages at any proportion, but there was an enhancement in the lymphoproliferative response when the lymphocytes from BCG-immunized rats were incubated with alveolar macrophages at the ratio of 100:1. The supernatant of alveolar macrophage cultures from both normal and BCG-immunized rats showed a suppressive effect on lymphocytes while the supernatant of lymphocyte-alveolar macrophage cultures from BCG-immunized rats enhanced the lymphoproliferation. The results indicate that there are soluble factors elaborated by alveolar macrophages which have opposite effects on lymphoproliferation, and that these factors may be involved in the development of the hyperimmune state of the lung in tuberculosis.