Specific IgG antibody responses may be used to monitor leprosy treatment efficacy and as recurrence prognostic markers.

Although curable, leprosy requires better diagnostic and prognostic tools to accompany therapeutic strategies. We evaluated the serum samples of leprosy patients from Venezuela and Brazil for reactivity against the specific recombinant proteins, ML0405 and ML2331, and the LID-1 fusion protein that incorporates both of these antigens. Antigen-specific IgG was highest in lepromatous leprosy patients (LL) and decreased across the disease spectrum, such that only a small subset of true tuberculoid patients (TT) tested positive. The impact of multidrug therapy (MDT) on these antibody responses was also examined. Several years after treatment, the vast majority of Venezuelan patients did not possess circulating anti-LID-1, anti-ML0405, and anti-ML2331 IgG, and the seropositivity of the remaining cases could be attributed to irregular treatment. At discharge, the magnitude and proportion of positive responses of Brazilian patients against the proteins and phenolic glycolipid (PGL)-I were lower for most of the clinical forms. The monthly examination of IgG levels in LL patient sera after MDT initiation indicated that these responses are significantly reduced during treatment. Thus, responses against these antigens positively correlate with bacillary load, clinical forms, and operational classification at diagnosis. Our data indicate that these responses could be employed as an auxiliary tool for the assessment of treatment efficacy and disease relapse.