Effects of opsonization of Rhodococcus equi on bacterial viability and phagocyte activation.
OBJECTIVE
To investigate the effect of opsonization of Rhodococcus equi with R. equi-specific antibodies in plasma on bacterial viability and phagocyte activation in a cell culture model of infection.


METHODS
Neutrophils and monocyte-derived macrophages from 6 healthy 1-week-old foals and 1 adult horse.


METHODS
Foal and adult horse phagocytes were incubated with either opsonized or nonopsonized bacteria. Opsonization was achieved by use of plasma containing high or low concentrations of R. equi-specific antibodies. Phagocyte oxidative burst activity was measured by use of flow cytometry, and macrophage tumor necrosis factor (TNF)-α production was measured via an ELISA. Extracellular and intracellular bacterial viability was measured with a novel R. equi-luciferase construct that used a luminometer.


RESULTS
Opsonized bacteria increased oxidative burst activity in adult horse phagocytes, and neutrophil activity was dependent on the concentration of specific antibody. Secretion of TNF-α was higher in macrophages infected with opsonized bacteria. Opsonization had no significant effect on bacterial viability in macrophages; however, extracellular bacterial viability was decreased in broth containing plasma with R. equi-specific antibodies, compared with viability in broth alone.


CONCLUSIONS
The use of plasma enriched with specific antibodies for the opsonization of R. equi increased the activation of phagocytes and decreased bacterial viability in the extracellular space. Although opsonized R. equi increased TNF-α secretion and oxidative burst in macrophages, additional factors may be necessary for effective intracellular bacterial killing. These data have suggested a possible role of plasma antibody in protection of foals from R. equi pneumonia.
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Dominic R
DR
Dawson
Daryl V
DV
Nydam
Christopher T
CT
Price
James E
JE
Graham
Michael H
MH
Cynamon
Thomas J
TJ
Divers
Maria Julia B
MJ
Felippe
D000193:Actinomycetales Infections / Q000276:immunology / Q000662:veterinary*; D000818:Animals; D000831:Animals, Newborn; D000907:Antibodies, Bacterial / Q000097:blood / Q000276:immunology; D001426:Bacterial Proteins / Q000097:blood / Q000276:immunology; D001996:Bronchopneumonia / Q000276:immunology / Q000662:veterinary*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005260:Female; D006734:Horse Diseases / Q000276:immunology*; D006736:Horses; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D008297:Male; D050296:Microbial Viability; D009504:Neutrophils / Q000276:immunology / Q000378:metabolism; D009895:Opsonin Proteins / Q000378:metabolism*; D010586:Phagocytes / Q000276:immunology / Q000378:metabolism; D010587:Phagocytosis; D016897:Respiratory Burst; D016929:Rhodococcus equi / Q000276:immunology* / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; D009895:Opsonin Proteins; D014409:Tumor Necrosis Factor-alpha