An assay for antibodies in leprosy sera reacting with ribonucleoprotein (RNP), a mycobacterial ribosomal antigen, using crossed immunoelectrophoresis with intermediate gel.

The technique of crossed immunoelectrophoresis with intermediate gel has been adapted to provide a quantitative assay for antibodies to a mycobacterial ribosomal antigen termed ribonucleoprotein (RNP) antigen. This antigen is no. 1 in the M. smegmatis reference system and corresponds to antigen no. 5 of M. leprae. The assay method measures changes in the rate of migration of the reference precipitin peak caused by the addition of serum in the intermediate gel and utilizes a lepromatous serum pool (LSP) both in the reference gel and as a standard in the intermediate gel. The anti-RNP activity in 24 leprosy sera differentiated the pauci-bacillary tuberculoid group (11 of 12 < 35% LSP) from the multi-bacillary lepromatous group (11 of 12 > 35% LSP). These findings confirm the work of others which indicates that assay of anti-RNP activity may have applications in the classification of leprosy patients and in the serodiagnosis of lepromatous leprosy infections. This method should also be applicable in other systems in which an antigen of high electrophoretic mobility forms a major precipitin in crossed immunoelectrophoresis.