Secretory and Accessory Cell Functions of the Alveolar Macrophage

We have attempted to address the requirements necessary for alveolar macrophage accessory cell function. We have also examined the in vitro and in vivo factors that must be taken into account when interpreting results from experimental studies. Differences in phenotypic expression by rat alveolar pleural and peritoneal macrophages are noted, as well as the differing expression of major histocompatibility complex (MHC) class II molecules. Furthermore, alveolar macrophages, harvested from rat lung, do not express the interleukin (IL)- cytokines, and lipopolysaccharide (LPS) treatment of quiescent cells (after 24-hrin vito culure) induces low levelsof exprssion of IL- a and IL-. Short-term inhalation of refractory ceramic fibers, however, resultsin markedly increased I-1 expression after stimulation with LPS e suggest that, in vivo, IL-O may be involved in the initial recruitment and activation of inflammatory cells rather than in induction of immune responses. We also postulate, based on recent published evidence, that alveolar macrophages activate the dendritic cells within the respiratory epithelium. Thus alveolar macrophages would release cytokines critical for the activation of dendritic cells during the afferent limb of the immune response, and they would respond to products of sensitized T-cells such as interfe and to interact with T-helper cells in an antigen-specific M C-restricted manner during the efferent limb of the response.