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.

Diagnosis and management of pulmonary infection due to Rhodococcus equi

“…A role for humoral immunity has not been conclusively demonstrated [44,45]. Antibody to VAPA has been identified in studies of convalescent patient sera [46,47], and its use has been suggested as a diagnostic tool [48].…”

Primary retroperitoneal abscesses due to Rhodococcus equi in a patient with severe nephrotic syndrome: successful antibiotic treatment with linezolid and tigecycline

“…14 On the other hand, both cellular and humoral immunity play a crucial role in the host response against R. equi. 15,16 In the present patient, the main predisposing factor was the severe immunocompromise due to nephrotic syndrome treated with prolonged steroid therapy. He had an immunoglobulin deficit due to persistent proteinuria (22-30 g/24 h) and also a severe lymphopenia, which might have contributed to the development of the disease.…”

Rhodococcus equiinfection of monocytes/macrophages from human immunodeficiency virus (HIV)-infected patients and healthy individuals: evaluation of intracellular killing and nitric oxide production

“…239D was a virulent strain containing the 85‐kb plasmid and expressing the virulence lipoprotein (VapA) associated with virulence in mice [21], whereas 210D was an avirulent strain. The presence of the virulence‐associated plasmid and protein was confirmed by agarose gel electrophoresis and immunoblotting, respectively, as previously described [8, 9]. Virulent strain 103 + and its plasmid‐cured derivative 103 − were of horse origin and they were kindly provided by Dr. J.F.…”