Beyond antibody titers: Corticosteroid effects on IgG avidity dynamics in experimental strongyloidiasis

Strongyloidiasis is a neglected tropical disease caused by Strongyloides spp., capable of lifelong persistence and fatal hyperinfection or dissemination in immunosuppressed individuals. Animal models play a key role in understanding host immune responses and improving diagnostics. This study evaluated the effects of dexamethasone and prednisolone, administered orally or subcutaneously, on the humoral immune response in a Strongyloides venezuelensis rat model. IgG kinetics and antibody avidity were analyzed by ELISA. Infected control animals seroconverted 8 days post infection (dpi), with all positive samples by 13 dpi. In contrast, corticosteroid-treated groups showed delayed or reduced IgG production. Oral dexamethasone allowed transient IgG detection 8 dpi, with seroconversion only 21 dpi, while subcutaneous dexamethasone nearly eliminated the response/detection. Oral prednisolone caused delayed seroconversion, with full positivity only 30 dpi. Subcutaneous prednisolone delayed IgG detection until 21 dpi. Antibody avidity remained mostly unchanged across treatments. However, prednisolone treatment (both oral and subcutaneous routes) increased avidity index (AI) at 21 dpi (AI: >74 vs. 41.45 in controls), suggesting preserved or enhanced affinity maturation despite immunosuppression. These findings show that corticosteroids suppress antibody levels but may not impair, and can even enhance, antibody maturation. Avidity testing may improve serodiagnosis and risk assessment in immunocompromised individuals with suspected strongyloidiasis.