Identification of antibodies directed against O-acetylated sialic acids invisceral leishmaniasis: its diagnostic and prognostic role

A significantly increased O-acetylated sialic acid (O-AcSA) binding fractio n was purified from serum of visceral leishmaniasis (VL) patients by affini ty chromatography on immobilized bovine submaxillary mucin (BSM) and found to be immunoglobulin in origin. The serodiagnostic and prognostic potential of BSM as a capture antigen was established by ELISA with no cross reactiv ity with coendemic diseases like malaria, tuberculosis, leprosy, chagas dis ease and cutaneous leishmaniasis; however, a strong cross reactivity was pr esent with trypanosomiasis patients. In 56 clinically diagnosed VL patients , the BSM-ELISA was compared with diagnosis by microscopy using Giemsa stai ned tissue smears and direct ELISA using crude parasite antigen (parasite-E LISA); 49/56(87.5%) and 5/56(9.0%) were positive and negative respectively by all 3 methods. The BSM-ELISA failed to diagnose 2/56(3.5%) patients whic h were biopsy and parasite-ELISA positive. The prognostic potential of the BSM-ELISA in 18 longitudinally monitored VL patients before and after conve ntional antimonial treatment showed a significant decrease in anti O-AcSA t itres in drug responsive patients whereas anti O-AcSA levels persisted in d rug unresponsive patients. The IgG subclass distribution of antibodies dire cted against O-AcSA showed increased IgG2 levels in VL patients as compared to healthy controls. The BSM-based ELISA holds great promise as a serodiag nostic and prognostic assay for VL.