Caco-2 Cell Co-Culture Alters the Molecular Size of Igl1 and Its Extracellular Fragments in Entamoeba histolytica

The galactose/N-acetyl-D-galactosamine (Gal/GalNAc)-inhibitable lectin of Entamoeba histolytica plays essential roles in host cell adhesion and cytotoxicity. The intermediate subunit lectin-1 (Igl1) contributes to these functions, but its molecular state under different environmental conditions remains unclear. In this study, we found that Igl1 is present as multiple fragments in the culture supernatant of trophozoites, whereas a single major species corresponding to intact Igl1 was detected in cell lysates. Notably, the molecular sizes of both intact Igl1 and its extracellular fragments differed depending on culture conditions, with larger apparent sizes observed under co-culture with Caco-2 cells. These differences were not explained by changes in transcript levels, protein folding, or N-terminal truncation. Fragmentation of Igl1 was suppressed by a cysteine protease inhibitor, indicating extracellular generation. These findings demonstrate that host-cell-associated conditions alter the molecular size of Igl1 and that extracellular protease-dependent processing generates multiple Igl1 fragments, providing new insights into the regulation of this key virulence factor. The presence of extracellular fragments further suggests a potential contribution to host tissue damage during amoebiasis.