IgM antibodies against M. leprae-PGL-I are specific for infection with mycobacteria causing leprosy (Hunter and Brennan, 1981; van Dijk et al., 2021) and anti-PGL-I IgM levels have been amply shown to be quantitively associated with bacterial load in leprosy patients (Zenha et al., 2009; van Hooij et al., 2017; Tió-Coma et al., 2020). The gene discussed is CD40LG; the disease is infection.