Modulation of macrophage functions by components of Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite and the causative agent of amebiasis. Activated macrophages are the main host effector cells in host defence against E. histolytica, through the production of nitric oxide (NO) which is cytotoxic for the parasite. NO is upregulated by tumor necrosis factor-alpha (TNF-$ alpha$) produced by macrophages. The objective of this study was to determine the effect of amebic components on TNF-$ alpha$ and NO production by macrophages. Soluble E. histolytica proteins stimulated naive macrophages for enhanced TNF-$ alpha$ mRNA expression through PKC signal transduction. E. histolytica-induced TNF-$ alpha$ mRNA expression was unstable, and macrophages pretreated with E. histolytica proteins expressed reduced levels of TNF-$ alpha$ mRNA in response to LPS or IFN-$ gamma$ + LPS. In contrast, the purified galactose-adherence lectin (Gal-lectin) of E. histolytica stimulated naive macrophages for stable TNF-$ alpha$ mRNA expression and protein production. Furthermore, IFN-$ gamma$ primed macrophages produced TNF-$ alpha$ and NO in response to the Gal-lectin. Naive macrophages exposed to Gal-lectin + IFN-$ gamma$ were activated to kill E. histolytica trophozoites in vitro by NO. Anti-lectin monoclonal antibodies that recognize non-overlapping epitopes of the kDa heavy subunit of the Gal-lectin identified amino acids 596-1082 as important in mediating amebic adherence to target cells and TNF-$ alpha$ mRNA induction in macrophages. Likewise, a region between amino acids 596-818 of the 170 kDa Gal-lectin, in conjunction with IFN-$ gamma$, activated macrophages for TNF-$ alpha$ and NO production and amebicidal activity. This research demonstrates the immunogenic potential of the E. histolytica Gal-lectin and the critical regions that could be used as a subunit vaccine candidate against amebiasis