Serum Anti-PGL-1 IgG, IgM, and IgA in a 3-Year Follow-up Study of 4-15-Year-old Leprosy Contacts.

Background: In 2015, the detection rate of leprosy in Santana do Ipanema municipality, Alagoas state, Brazil, was 39.3 cases per 100,000 inhabitants, and among young people below 15 years of age, it was 32.8 cases per 100,000 inhabitants.
Material and Methods: A prospective study was carried out from 2015 to 2017, in Santana do Ipanema city, with 69 leprosy contacts in the age group of 4-15 years. Measurement of serum IgM, IgG, and IgA against phenolic glycolipid antigen-1 (PGL-1) was done by an indirect enzyme-linked immunosorbent assay.
Results: A high frequency of positive anti-PGL-1 IgM was found in both paucibacillary and multibacillary contacts. Twenty-three participants presented suspected lesions and 45 did not. In both groups a high frequency of positive IgM was found. In regard to anti-PGL-1 IgG, it was found a strong association between its positivity and the presence of lesions (relative risk of 3.25). Eight new cases of leprosy were diagnosed, five of which were seropositive for anti-PGL-1. Again, a striking association was found between positive IgG and leprosy (relative risk of 8.5). No significant association was found between IgM isotype and disease, nor between IgA and disease.
Conclusions: The present study reinforces the importance of measuring the three anti-PGL-1 isotypes in follow-up studies of leprosy contacts. Moreover, positive anti-PGL-1 IgG is associated with a high associated risk of disease.