Antigen-presenting function of alveolar macrophages: uptake and presentation of Listeria monocytogenes.

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Abstract
Mouse alveolar macrophages were characterized and compared to resident peritoneal macrophages for their ability to take up and present to immune T cells the bacteria Listeria monocytogenes. Both macrophage populations contained a similar proportion of Ia-positive macrophages (approximately 5%). However, alveolar macrophages showed a deficiency in the uptake of Listeria monocytogenes. Macrophage, antigen-presenting function was studied by measuring the proliferative response of Listeria-immune T cells to Listeria-pulsed macrophages. The alveolar macrophages were capable of presenting Listeria, although less effectively than the peritoneal macrophages. Listeria presentation by alveolar macrophages was dose dependent, antigen specific, and genetically restricted, and required the presence of Ia-positive macrophages. The differences in antigen-presenting function between alveolar and peritoneal macrophages appeared to be due solely to their differences in Listeria uptake. Thus, opsonizing Listeria resulted in marked enhancement of both Listeria uptake and presentation by alveolar macrophages. These findings demonstrate that alveolar macrophages possess I-region-dependent antigen-presenting function and emphasize the importance of bacterial binding by macrophages in generating effective immune stimulation.