Interaction of Rhodococcus equi with phagocytic cells from R. equi-exposed and non-exposed foals

• Published in: Veterinary microbiology Vol. 14; no. 3; pp. 307 - 320
• Main Authors: Hietala, S.K., Ardans, A.A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.08.1987
• Subjects: Actinomycetales Infections - physiopathology; Actinomycetales Infections - veterinary; Animals; Animals, Newborn; Female; Horse Diseases - microbiology; Horse Diseases - physiopathology; Horses - physiology; In Vitro Techniques; Macrophages - physiology; Macrophages - ultrastructure; Opsonin Proteins - immunology; Pulmonary Alveoli - cytology; Rhodococcus - physiology; Rhodococcus - ultrastructure; Rhodococcus equi
• ISSN: 0378-1135; 1873-2542
• DOI: 10.1016/0378-1135(87)90118-0

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<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 > 65% of the infective dose by 6 h post-exposure. Alveolar macrophages from sensitized foals behaved as adult macrophages, able to kill > 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 > 100% increase in killing capacity.