Immunoglobulin G1 (IgG1) and IgG3 antibodies are markers of progressive disease in leprosy.

Mycobacterium leprae-specific and polyclonal immunoglobulin G (IgG) subclass and IgE antibodies in leprosy patients across the histopathological spectrum were determined by using a quantitative enzyme-linked immunosorbent assay. Antibody responses to M. leprae sonicates were detected only in IgG1, -2, and -3 subclasses. Even at 100-times-lower dilutions, very little IgG4 and IgE antibody activity against M. leprae was detected in any group of leprosy patients. Quantitatively, antibody responses were highest at the lepromatous pole and decreased towards the tuberculoid pole. The greatest quantitative difference in antibodies between the lepromatous and tuberculoid poles was observed with IgG1 (140-fold), this was followed by the difference with IgG3 antibodies (32-fold). Polyclonal antibodies, on the other hand, were elevated for all four IgG subclasses as well as IgE in both lepromatous and tuberculoid leprosy patients compared with healthy controls from a leprosy-endemic area. Selective elevation of M. leprae-specific antibody responses in IgG1 and IgG3 subclasses, therefore, could not be attributed to selective polyclonal activation in these particular subclasses. Furthermore, polyclonal activation for IgE was observed in both lepromatous and tuberculoid leprosy patients, with higher levels in the tuberculoid group, which does not support selective TH2 activation in lepromatous leprosy patients. IgG1 and IgG3 antibodies also showed the highest Spearman rank correlation with the bacterial index in these patients (rho = 0.748 and P < 0.001 for IgG1; rho = 0.721 and and P < 0.001 for IgG3). Thus, disease progression in leprosy showed a significant correlation with selective increases in IgG1 and IgG3 responses.