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Infection and Immunity, November 2005, p. 7697-7704, Vol. 73, No. 11
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.11.7697-7704.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Apical Spore Phagocytosis Is Not a Significant Route of Infection of Differentiated Enterocytes by Encephalitozoon intestinalis

Gordon J. Leitch,1* Tarsha L. Ward,1 Andrew P. Shaw,1 and Gale Newman2

Department of Physiology,1 Department of Microbiology, Biochemistry and Immunology, Morehouse School of Medicine, Atlanta, Georgia 303102

Received 5 July 2005/ Returned for modification 18 July 2005/ Accepted 24 July 2005

Encephalitozoon intestinalis is a microsporidian species that infects the intestinal mucosal epithelium, primarily in immunodeficient individuals. The present study employed undifferentiated and differentiated human colonic carcinoma cell lines to determine if this parasite species infected polarized epithelial cells by spore phagocytosis or by impalement with the deployed spore polar tube. Apical surface spore attachment differed between cell lines such that SW480>HT-29>Caco-2>HCT-8, with attachment being greater to undifferentiated Caco-2 cells than differentiated cells and greater to partially differentiated HCT-8 cells than differentiated HCT-8 cells. Attachment was inhibited by chondroitin sulfate A, suggesting that it was mediated by host cell sulfated glycoaminoglycans. Infection rates 3 days postinfection paralleled spore attachment in the various cell lines. The undifferentiated cell line SW480 and undifferentiated Caco-2 and HCT-8 cells exhibited modest spore phagocytosis while the more differentiated cell line HT29 and differentiated Caco-2 and HCT-8 cells did not. All cell lines were impaled by the polar tubes of germinating spores. When normalized to the number of spores attached to the apical membrane, such impalement was greatest in the more differentiated Caco-2 and HCT-8 cells. The host cell apical surface influenced parasite spore germination, as in populations of large undifferentiated Caco-2 cells to which >3 spores had attached, the frequency distribution of the percentages of spores germinated per cell was bimodal, indicating that the surface of some cells favored germination, while others did not. This study suggests that phagocytosis is not a biologically significant mode of infection in differentiated intestinal epithelial cells.

* Corresponding author. Mailing address: Department of Physiology, Morehouse School of Medicine, 720 Westview Dr., Atlanta, GA 30310. Phone: (404) 752-1681. Fax: (404) 752-1045. E-mail: gleitch{at}msm.edu.

Editor: A. Casadevall

Infection and Immunity, November 2005, p. 7697-7704, Vol. 73, No. 11
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.11.7697-7704.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.





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