A specific immunodominant 54-kDa
antigen was 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 (immunoblot) technique was applied to detecting the immunologic response to nocardiae in the serum of
nocardiosis patients. Each of the 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. There was no reaction to either the 54- or the 31-kDa
antigen with all serum samples obtained from patients with
tuberculosis, except for one, with all serum samples obtained from patients with
leprosy, or with all sera obtained from healthy controls. The partially purified 54-kDa
antigen, specific for N. asteroides, was used as the immunogen to generate
monoclonal antibodies (mAbs) and two mAbs were selected. As determined by Western blot, both mAbs reacted with the 54-kDa band. Using indirect immunofluorescence or
enzyme immunoassay with whole N. asteroides micro-organisms, the mAbs did not react with N. asteroides cells. No cross-reactivity with mycobacterial
antigens, either culture-filtrate
antigens or
tuberculin, was exhibited with any of the two mAbs. These mAbs are candidates to be used for the development of a sensitive and specific diagnostic test for
nocardiosis.