A subunit vaccine candidate region of the Entamoeba histolytica galactose-adherence lectin promotes interleukin-12 gene transcription and protein production in human macrophages

The cysteine-rich region of the 170-kDa subunit galactose-adherence lectin (Gal-lectin) of Entamoeba histolytica is a subunit vaccine candidate and a protective antigen in the gerbil model of amebiasis. Macrophage-mediated im munity is important for protection against E. histolytica and is activated by Th1 cytokines. As Th1 differentiation is promoted by IL-12, we investiga ted what portion of the Gal-lectin could stimulate IL-12 in human THP-1 mac rophages. Native Gal-lactin stimulated IL-12 p40/p35 mRNA expression in a d ose- and time-dependent manner as measured by reverse transcriptase-PCR. Hu man immune serum and Gal-lectin mAb inhibition studies identified amino aci ds (aa) 596-998 as immunogenic and containing the IL-12 inducing domain, IF N-gamma priming augmented Gal-lectin-induced IL-12 mRNA expression independ ent of TNF-alpha and IL-1 beta, and was required for IL-12 p70 protein prod uction from macrophages and human peripheral blood mononuclear cells. Gal-l ectin plus IFN-gamma stimulated IL-12 p40 and p35 gene transcription with s table mRNA transcripts and a differential requirement for protein synthesis . These results suggest that aa 596-998 of the Gal-lectin can confer Th1-me diated protection against amebiasis through IL-12 induction.