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

To examine the relationship between phagocytosis, proteinase activity and pathogenicity of axenically grown trophozoites of E. histolytica strain HM-1:IMSS four different cultures were used: (1) a culture preserved in our laboratory for over 4 years, which lost its pathogenicity 3 years ago; (2) a culture passaged several times through hamster liver, which lost its pathogenicity recently; (3) a highly virulent culture supplied by another laboratory; and (4) amebas recovered from hamster liver abscesses caused by culture 3. 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 showed wide variations through a 2-month observation period, with no change in amebic pathogenicity. No correlation was found between the level of proteinase activity and pathogenicity. It is concluded that neither phagocytosis nor proteinase activity is an adequate marker of amebic pathogenicity.