Phagocytosis and proteinase activity are not related to pathogenicity of Entamoeba histolytica.

To examine the relationship between phagocytosis, proteinase activity and pathogenicity of axenically grown trophozoites of E. histolytica of strain HM-1:IMSS four different cultures were used: 1) a culture preserved in our laboratory for over 4 years, that lost its pathogenicity 3 years ago; 2) a culture passaged several times through hamster liver, that lost its pathogenicity recently; 3) a highly virulent culture supplied by another laboratory; and 4) amebas recovered from hamster liver abscesses caused by the latter culture. Phagocytosis was measured as erythrophagocytosis. Proteinase activity was determined on azocasein. Pathogenicity was defined as the capacity to cause liver abscesses in hamsters. A negative correlation was found between phagocytic activity and pathogenicity, since amebas unable to cause liver abscesses had the highest phagocytic activity whereas those recovered from liver abscesses had the lowest phagocytic activity. The percent of phagocytic amebas increased progressively in all cultures through a 2-month observation period. No correlation was found between the level of proteinase activity and pathogenicity. It is concluded that neither phagocytosis nor proteinase activity are adequate markers of amebic pathogenicity.