The humoral response to PGL-I in leprosy patients, mainly IgM, correlates very well with the BI (bacillary index) and is highly specific, and the anti-PGL-I titer can be easily assessed using either the standard ELISA assay or in a lateral flow device [13–16] using the synthetic di- or trisaccharide of PGL-I linked to a protein carrier, bovine or human serum albumin (BSA or HSA) derivatives. The gene discussed is CD40LG; the disease is leprosy.