Alveolar macrophages form the first line of defense in the lung against a variety of intracellular parasites. However, the precise relationship between these cells and the immunologically activated emigrant monocytes which enter the developing lesion is still not clear. Several representative microbial lung pathogens will be introduced by the aerogenic and intravenous routes into LBN rats and B6D2 mice. The effect of these infections on the mononuclear phagocytes present in the lungs following the two types of challenge will be examined and compared with available data obtained using live and heat-killed BCG suspensions. The effect of a variety of chemotherapeutic and immunotherapeutic regimens on the establishment and persistence of atypical Mycobacteria in the lungs of aerogenically infected rats and mice will be made, correlating the antibacterial response with the level of DTH or anergy present in the heavily infected animals. The effect of the thymic hormone 'thymosin' on the ability of BCG vaccines to promote an anti-Mycobacterial immune response within the lung will be explored quantitatively. Several atypical Mycobacterial (M. kansasii, M. simiae, M. intracellulare) cause persisting systemic infections associated with a lack of cell-mediated immunity and a profound anergy. The role played by suppressor T and B cells in the establishment of these persisting infections in rat and mouse lung will be examined both in vivo and in vitro and correlated with levels of DTH and CMI. The effects of chemotherapy, cyclophosphamide, and thymosin treatment on suppressor T-cell activity by spleen, lung and tracheobronchial lymphocytes will be assessed in terms of humoral and cellular immune responses within the lungs of heavily infected animals to be used as a therapeutic model of human lung infections.