Rhodococcus equi Virulence-Associated Antigens and Specific Antibody Response in AIDS Patients Infected with R. equi.
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.
Mastroianni
Claudio Maria
CM
Department of Infectious and Tropical Diseases, La Sapienza University, Rome, Italy.
Lichtner
Miriam
M
Mengoni
Fabio
F
Mascellino
Maria Teresa
MT
Vullo
Vincenzo
V
Delia
Salvatore
S