title: Interaction of Rhodococcus equi with phagocytic cells from R. equi-exposed and non-exposed foals.
abstract: The interaction of Rhodococcus equi with alveolar macrophages from adult horses, foals experimentally exposed to R. equi (sensitized foals) and non-exposed foals was studied using in vitro bactericidal assays, cytochemical staining and transmission electron microscopy. It was demonstrated that R. equi is a facultative intracellular parasite, able to survive and multiply within the alveolar macrophages of the host by interfering with phagosome-lysosome fusion. Opsonization of R. equi with antibody against capsular components was associated with increased phagosome-lysosome fusion and significantly enhanced (P less than 0.05) killing of the organism by alveolar macrophages from non-exposed foals. Macrophages from non-exposed foals were able to ingest the non-opsonized organism, but unable to kill greater than 65% of the infective dose by 6 h post-exposure. Alveolar macrophages from sensitized foals behaved as adult macrophages, able to kill greater than 95% of the infective dose by 6 h. Lymphocyte factors, derived by in vitro incubation of sensitized peripheral blood lymphocytes with R. equi surface antigens, enhanced macrophage bactericidal activity. Macrophages from non-exposed foals incubated in the presence of the lymphocyte factors had a 50% increase in killing of R. equi, while sensitized macrophages incubated with lymphocyte factors had a greater than 100% increase in killing capacity.
authors: Department of Medicine, School of Veterinary Medicine, University of California, Davis 95616.
authors: S K
authors: SK
authors: Hietala
authors: A A
authors: AA
authors: Ardans
mesh_terms: D000193:Actinomycetales Infections / Q000503:physiopathology / Q000662:veterinary*; D000818:Animals; D000831:Animals, Newborn; D005260:Female; D006734:Horse Diseases / Q000382:microbiology* / Q000503:physiopathology; D006736:Horses / Q000502:physiology*; D066298:In Vitro Techniques; D008264:Macrophages / Q000502:physiology* / Q000648:ultrastructure; D009895:Opsonin Proteins / Q000276:immunology; D011650:Pulmonary Alveoli / Q000166:cytology*; D012240:Rhodococcus / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D009895:Opsonin Proteins