Murine immunological and histological changes in response to chronic silica exposure

The relationship between immunological and histological changes was studied in mice exposed to silica dust over a period of 39 weeks. The response of these mice to Escherichia coli antigens given as an aerosol was suppressed in the spleen at all times tested, while in the mediastinal lymph nodes (MLN) an initial enhancement at 9 weeks was followed by suppression of responses at all subsequent times.The development of silica-induced lesions also was studied using histological methods. With polarized light, silica-laden aggregations of macrophages were observed in the lungs after 24, 33, 36, and 39 weeks. Using scanning electron microscopy, numerous macrophages were frequently present in respiratory airways of silica-exposed animals. Typical silicotic lesions were observed in lungs and adjacent lymph nodes after 39 weeks of exposure.