Detection of IgA anti-PGL-I specific antigen to Mycobacterium leprae in mangabey monkeys inoculated with M. leprae

Using sera from 4 pairs of mangabey monkeys inoculated with titrated doses of Mycobacterium leprae we demonstrated that IgA antibodies against M. leprae specific PGL-I antigen were present in 75% of inoculated monkey's sera. High IgA antibody was detected in 50% (3/6) of infected animals and all three developed lepromatous leprosy (LL). Antibody titers correlated with PGL-I antigen in serum. The highest IgA peak appeared late and corresponded to the beginning of treatment, and in two of them appeared shortly after or corresponded with neurological damage. Low IgA response was found in the other 3 monkeys (50%-3/6), two of which developed indeterminate leprosy (I) and the other one LL. Low IgA levels appeared late after IgG and IgM, and shortly after neurologic signs. Both I monkeys were negative for PGL-I in serum. The remaining 2 monkeys (25%-2/8) did not show an IgA response; one of them developed LL but the disease regressed to I. IgM seemed to correspond to the appearance of PGL-I in serum. The other animal did not develop clinical symptoms of leprosy, and PGL-I in serum was negative. Although there was no clear relation between the development of anti-PGL-I IgA and experimental leprosy, the finding of a high IgA response in some animals suggests that further studies are needed to evaluate the role of antigen-specific IgA in the disease process.