Class specific anti-Mycobacterium leprae antibody assay in lepromatous leprosy (BL-LL) patients during the first two to four years of DDS treatment.

: Previously, a slight decrease in antibodies against M. leprae antigen 7 was demonstrated after one year of dapsone (DDS) treatment in 14 of 15 patients with lepromatous (BL-LL) leprosy. The same patients have now received DDS from 11/2 to 4 years (median 3 years) and sera taken at the start, during, and at the end of the observation period have been retested for antibodies against M. leprae antigen 7 by radioimmunoassay and tested for IgA-, IgM-, and IgG-anti-M. leprae antibody activity by solid phase radioimmunoassay. Both IgA- and IgG-anti-M. leprae antibody activity and the activity of antibodies against M. leprae antigen 7 showed a decrease in activity after three years of DDS treatment to a median value of about one third of the activity in the sera taken at the start of the study. A smaller but significant decrease in IgM-anti-M. leprae antibody activity could be demonstrated. A transient increase in antibody activity (both measured by RIA and sRIA) could be demonstrated and related to reactions (reversal reaction and ENL) in five patients. No significant correlation could be found when IgA-, IgM-, and IgG-anti-M. leprae antibody activity was compared with antibodies against M. Leprae antigen 7 in individual sera.