Serologic responses toRhodococcus equi in individuals with and without human immunodeficiency virus infection

Abstract

Thirty healthy blood donors, 15 workers from horse-breeding farms, 69 human immunodeficiency virus (HIV)-negative persons at risk for HIV infection, 125 HIV-infected subjects withoutRhodococcus equi infection, and nine HIV-infected patients withRhodococcus equi pneumonia were evaluated in order to detect serum antibodies toRhodococcus equi precipitate-soluble antigen by an enzyme immunoassay (EIA). Whereas EIA values for healthy donors, horse farm workers, individuals at risk for HIV infection, and HIV-positive subjects withoutRhodococcus equi infection were comparable, HIV-infected patients with rhodococcal disease had significantly higherRhodococcus equi antibody levels (p<0.0001). The clinical outcome ofRhodococcus equi pneumonia was more severe in subjects who had low levels of specific antibodies, whereas patients who recovered had elevatedRhodococcus equi antibody levels over time. Immunoblot studies showed that bothRhodococcus equi-infected patients and foals recognized a protein band of approximately 60 kDa in theRhodococcus equi precipitate-soluble antigen. On the other hand, theRhodococcus equi-infected patients did not react with the diffuse 15 to 17 kDa virulence-associated proteins that represent important virulence factors both in mice and horses.