Serologic responses to nerve antigens in sooty mangabey monkeys with experimental leprosy

Eight sooty mangabey monkeys were inoculated intravenously and intradermally with varying doses of Mycobacterium leprae from 4.8 x 10⁷ to 4.8 x 10¹⁰. Serum samples were obtained from the animals at intervals of about 3 months for 90 months, and were examined for IgM and IgG antibodies to nerve antigens, including ceramide, galactocerebroside (GC), and asialo-GM₁ (AGM₁), using an enzyme-linked immunosorbent assay (ELISA). The serological results were then compared with clinical findings, particularly nerve involvement. Of 8 mangabey monkeys inoculated with M. leprae, 7 animals had clinical leprosy; 6 of them had nerve damage, including neurologic deformities in 4 monkeys and nerve enlargement in 2. Median time for the initial signs of leprosy was 10 months postinoculation (p.i.), a range from 4 to 35 months. In contrast, nerve damage was noted rather late, about 35 to 86 months p.i. (median 54 months). The major immunoglobulin class to ceramide, GC, and AGM₁ antigens was IgM, and the antibody responses to the nerve antigens appeared from 15 to 63 months p.i. (median 37 months). Antineural antibodies were thus detectable about 18 months (range -2 to 60 months) prior to observable nerve damage. In addition, elevation of antineural antibody levels were predictive of clinical exacerbation of the disease and neuritic damage. This study suggests that antineural antibodies are produced during the course of M. leprae infection and may be indicative of nerve damage, such as neurological deformities or nerve enlargement, in leprosy patients.