Intestinal infection with Giardia spp. reduces epithelial barrier function in a myosin light chain kinase-dependent fashion.
OBJECTIVE
Giardiasis causes malabsorptive diarrhea, and symptoms can be present in the absence of any significant morphologic injury to the intestinal mucosa. The effects of giardiasis on epithelial permeability in vivo remain unknown, and the role of T cells and myosin light chain kinase (MLCK) in altered intestinal barrier function is unclear. This study was conducted to determine whether Giardia spp. alters intestinal permeability in vivo, to assess whether these abnormalities are dependent on T cells, and to assess the role of MLCK in altered epithelial barrier function.


METHODS
Immunocompetent and isogenic athymic mice were inoculated with axenic Giardia muris trophozoites or sterile vehicle (control), then assessed for trophozoite colonization and gastrointestinal permeability. Mechanistic studies using nontransformed human duodenal epithelial monolayers (SCBN) determined the effects of Giardia on myosin light chain (MLC) phosphorylation, transepithelial fluorescein isothiocyanate-dextran fluxes, cytoskeletal F-actin, tight junctional zonula occludens-1 (ZO-1), and MLCK.


RESULTS
Giardia infection caused a significant increase in small intestinal, but not gastric or colonic, permeability that correlated with trophozoite colonization in both immunocompetent and athymic mice. In vitro, Giardia increased permeability and phosphorylation of MLC and reorganized F-actin and ZO-1. These alterations were abolished with an MLCK inhibitor.


CONCLUSIONS
Disruption of small intestinal barrier function is T cell independent, disappears on parasite clearance, and correlates with reorganization of cytoskeletal F-actin and tight junctional ZO-1 in an MLCK-dependent fashion.
D000199:Actins / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D005260:Female; D016829:Giardia lamblia / Q000254:growth & development* / Q000276:immunology; D005873:Giardiasis / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000201:enzymology* / Q000469:parasitology*; D007421:Intestine, Small / Q000166:cytology / Q000201:enzymology / Q000469:parasitology; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D008819:Mice, Nude; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D013047:Specific Pathogen-Free Organisms; D013601:T-Lymphocytes / Q000469:parasitology; D062826:Zonula Occludens-1 Protein
D000199:Actins; D008565:Membrane Proteins; D010750:Phosphoproteins; C569042:TJP1 protein, human; C569043:Tjp1 protein, mouse; D062826:Zonula Occludens-1 Protein; D009219:Myosin-Light-Chain Kinase