IDENTIFICATION OF IGM AS THE LEPROSY PATIENT SERUM FACTOR RESPONSIBLEFOR RAPID SEDIMENTATION OF FORMOLIZED SHEEP ERYTHROCYTES

The serum of some leprosy patients with impaired specific cellular imm unity for Mycobacterium leprae causes rapid sedimentation of formolize d sheep erythrocytes, a phenomenon known as the Rubino reaction. The R ubino factor was precipitated from positive sera by 5% (w/v) polyethyl ene glycol (PEG), bound to a concanavalin A (ConA)-Sepharose column an d eluted with D-mannose, and was also eluted from a Mono Q column, pH 8.0, with 0.4 M NaCl. The Rubino factor was eluted in a volume which c oincided with that of human serum IgM from a Sepharose 6 column. IgM w as present in the preparation obtained by this sequence of chromatogra phic procedures. The correspondence of IgM with the Rubino factor was demonstrated by the following data: a) the Rubino factor was adsorbed to rabbit IgG antihuman IgM-agarose and the activity was recovered in the acid eluate of the column; b) the Rubino reaction was inhibited in the presence of rabbit antihuman IgM antibodies. This behavior was no t observed when the same procedures were carried out using anti-alpha( 2)-macroglobulin antibodies as a control. The rapid sedimentation of f ormolized sheep red cells caused by the serum of lepromatous leprosy p atients was not inhibited by phenolic glycolipid-I, suggesting that th e IgM responsible for the Rubino reaction is not directed to this anti gen which is specific for M leprae. There was no correlation between t he positivity of the Rubino reaction and the increase in total serum I gM levels observed in 42% of the lepromatous patients evaluated. The d emonstration that the Rubino factor is an IgM now permits the identifi cation of the epitope recognized by it, and this may be used as a tool to understand the specific cellular immune unresponsiveness which cha racterizes lepromatous leprosy.