A scanning electron microscopic study of the early response of lung tissue to amosite asbestos exposure.

The early response of the lung to a single exposure of amosite asbestos was examined via scanning electron microscopy and correlated light microscopy in the guinea pig model. At 2 h post-exposure, lesions consisted of discrete areas of atelectasis with influx of neutrophils and macrophages. Free asbestos fibres were evident in affected areas. By 4 h post exposure, affected regions were more extensive with phagocytic cell numbers increased both in reactive sites and in adjacent tissue. By 1 day post-exposure, the inflammatory response was well developed and encompassed wide areas of the lung. Activated phagocytes were congregated in atelectatic regions and on blood vessel walls. Numerous macrophages were present even in alveoli distant to reactive loci. The 6 day and 12 day time frames marked a subsiding of the inflammatory response in which macrophages outnumbered PMNs in the comparably fewer reactive areas. There was a notable decrease both in marginated leucocytes and in accumulations of phagocytes in tissue adjacent to affected regions.