Use of partially purified 54-kilodalton antigen for diagnosis of nocardiosis by Western blot (immunoblot) assay.

A Western blot (immunoblot) assay is presented for the diagnosis of nocardiosis with a specific immunodominant 54-kilodalton (kDa) antigen purified from a culture filtrate of Nocardia asteroides by immunoaffinity chromatography. The chromatography column was prepared with immunoglobulin G obtained from sera from patients with lepromatous leprosy. Unbound solutes consisted of specific, partially purified N. asteroides antigens, primarily a 54-kDa band, accompanied by two others of 31 and 62 kDa. The Western blot technique was applied to detecting the immunologic response to nocardiae. Immunodetection was performed according to the biotin-avidin system, which greatly improved the detection of antibodies even in immunosuppressed hosts. Each of 16 serum samples from immunosuppressed or immunocompetent patients infected with N. asteroides reacted with the 54-kDa band, and two reacted with the 31- and 62-kDa bands. Each of the serum specimens obtained from patients with mycetoma caused by Nocardia brasiliensis or Rhodococcus rhodochrous reacted with the 54-kDa band. There was no reaction to either the 54- or the 31-kDa antigen with all serum samples obtained from patients with tuberculosis, except one, with all serum samples obtained from patients with leprosy, or with all sera obtained from healthy controls. The 54-kDa protein is a candidate to be used as a probe to study the humoral immunologic response to nocardiae.