Modeling Long-Term Host Cell-Giardia lamblia Interactions in an In Vitro Co-Culture System

Abstract

Globally, there are greater than 700,000 deaths per year associated with diarrheal disease. The flagellated intestinal parasite, Giardia lamblia, is one of the most common intestinal pathogens in both humans and animals throughout the world. While attached to the gastrointestinal epithelium, Giardia induces epithelial cell apoptosis, disrupts tight junctions, and increases intestinal permeability. The underlying cellular and molecular mechanisms of giardiasis, including the role lamina propria immune cells, such as macrophages, play in parasite control or clearance are poorly understood. Thus far, one of the major obstacles in ascertaining the mechanisms of Giardia pathology is the lack of a functionally relevant model for the long-term study of the parasite in vitro. Here we report on the development of an in vitro co-culture model which maintains the basolateral-apical architecture of the small intestine and allows for long-term survival of the parasite. Using transwell inserts, Caco-2 intestinal epithelial cells and IC-21 macrophages are co-cultured in the presence of Giardia trophozoites. Using the developed model, we show that Giardia trophozoites survive over 21 days and proliferate in a combination media of Caco-2 cell and Giardia medium. Giardia induces apoptosis of epithelial cells through caspase-3 activation and macrophages do not abrogate this response. Additionally, macrophages induce Caco-2 cells to secrete the pro-inflammatory cytokines, GRO and IL-8, a response abolished by Giardia indicating parasite induced suppression of the host immune response. The co-culture model provides additional complexity and information when compared to a single-cell model. This model will be a valuable tool for answering long-standing questions on host-parasite biology that may lead to discovery of new therapeutic interventions.

Advances in understanding Giardia: determinants and mechanisms of chronic sequelae

“…The persistent translocation of mucosally associated bacterial microbiota has been proposed to explain post-infection irritable bowel syndrome and chronic fatigue [ 31 ], sequelae present in up to 5% of individuals with prior giardiasis [ 136 ], particularly in those whose initial course was more protracted [ 137 ]. Mechanisms by which Giardia could influence microbiota composition include alterations in the luminal nutritional environment as previously stated, as well as dampening the epithelial cell inflammatory responses through post-translational reductions in IL-8 and decreased nitric oxide synthesis [ 102 , 120 , 138 – 140 ].…”

Giardia duodenalis Infection Reduces Granulocyte Infiltration in an In Vivo Model of Bacterial Toxin-Induced Colitis and Attenuates Inflammation in Human Intestinal Tissue

“…Previous research has suggested that Giardia excretory/secretory products induce IL-8/CXCL8 expression in intestinal epithelial cells [39] . However, we and others have demonstrated that Giardia trophozoites attenuate IL-8/CXCL8 secretion from in vitro epithelial monolayers [40] , [41] . Our research further demonstrated that Giardia cathepsin B family proteases contributed to the degradation of IL-8/CXCL8 and attenuated PMN chemotaxis [41] .…”

Long-Term Culture of Giardia lamblia in Cell Culture Medium Requires Intimate Association with Viable Mammalian Cells

“…Fisher et al (6) performed experiments and were able to grow Giardia in the presence of Caco2 cells with 10% TYI-S-33 and Dulbecco's modified Eagle's medium (DMEM) for up to 21 days in a transwell system. The purpose and design of their experiments were to study the interaction of Giardia with Caco2 cells, which contrasts with the biological questions studied and reported here.…”