Actin mediates Encephalitozoon intestinalis entry into the human enterocyte-like cell line, Caco-2

Microsporidia are spore-forming obligate intracellular eucaryotes that para sitize eukaryotic cells. Encephalitozoon intestinalis (formerly Septata int estinalis) is a microsporidian species of emerging medical importance, resp onsible for chronic diarrhoea in immunocompetent patients and enteritis and systemic infections in HIV-1 infected patients. Infection of host enterocy tes has been demonstrated in HIV-1-infected patients. However, the mechanis ms of entry of E. intestinalis into host enterocytes have not been studied and remain hypothetically based on diacytosis, a model involving the inject ion of microsporidian sporoplasm through the polar tubule into the host cel l. An electron microscopy based study recently challenged this hypothesis. We studied the entry of E. intestinalis into intestinal epithelial cells by infecting the human enterocyte-like cell line Caco-2. Entry was mediated b y directed phagocytosis, as suggested by the inhibiting effect of cytochala sin D on E. intestinalis uptake, colocalization of E, intestinalis and F-ac tin and engulfment of E. intestinalis into Caco-2 cell protrusions. Confoca l- and electron microscopy observations also suggested that after initial c ontacts through the posterior pole of the microsporidian spore, the basolat eral surface of Caco-2 cells may be the portal of entry for E. intestinalis sporoplasm. Our observations allowed us to propose a new, actin-based mode l to describe the entry of microsporidia into enterocytes. (C) 2000 Academi c Press.