title: Rhodococcus equi Virulence-Associated Antigens and Specific Antibody Response in AIDS Patients Infected with R. equi.
abstract: OBJECTIVES: To analyze the expression of the 15- to 17-kDa plasmid-encoded antigens from Rhodococcus equi isolates of 7 AIDS patients and determine the immunologic response to these proteins in the patients' sera. METHODS: The expression of the virulence proteins in R. equi isolates and the specific antibody response were investigated by immunoblotting. Plasmid DNA was analyzed by agarose gel electrophoresis. RESULTS: The only patient infected with a strain carrying the virulence 85-kb plasmid and expressing the 15- to 17-kDa antigens developed a fatal pneumonia and did not produce specific antibodies to the virulence proteins. Of the 6 patients infected with R. equi strains lacking both proteins and plasmid, only 1 subject had a pulmonary disease with poor clinical outcome and exhibited a negligible humoral immune response to R. equi antigenic components, whereas the other patients who produced a remarkable antibody response developed either an asymptomatic infection (1 case) or pneumonia (4 cases) which completely cleared up. CONCLUSIONS: Our findings suggest that R. equi disease can be induced without the expression of the 15- to 17-kDa virulence-associated plasmid-encoded antigens in HIV-infected patients with very low CD4+ cell counts. Nevertheless, both the synthesis of the virulence proteins and a defective humoral immune response to R. equi may contribute to the severity of rhodococcal disease.
authors.affiliation: Department of Infectious and Tropical Diseases, La Sapienza University, Rome, Italy.
authors.forename: Claudio Maria
authors.initials: CM
authors.lastname: Mastroianni
authors.forename: Miriam
authors.initials: M
authors.lastname: Lichtner
authors.forename: Fabio
authors.initials: F
authors.lastname: Mengoni
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Mascellino
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Vullo
authors.forename: Salvatore
authors.initials: S
authors.lastname: Delia