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.
Highlights
Giardia lamblia, known as G. intestinalis or G. duodenalis, is one of the most common intestinal protozoan parasites in humans, wildlife, and domestic animals
Osmotic stress-induced changes in tight junctions and cytokine secretion are both mediated through Mitogen-Activated Protein Kinases (MAPKs) [40,41], highly conserved protein kinases that function in vital cellular processes including cell cycle regulation, cell differentiation and proliferation, immune responses, and cell death
The three major MAPKs are extracellular signal-regulated kinase (ERK-1/2), which functions in differentiation and proliferation, the c-Jun N-terminal kinases (JNKs), and the stress-activated protein kinase (p38), which are involved in cellular response to stress
Summary
Known as G. intestinalis or G. duodenalis, is one of the most common intestinal protozoan parasites in humans, wildlife, and domestic animals. Due to its global distribution and significance, in September 2004, the World Health Organization (WHO) included Giardia lamblia on its ‘Neglected Disease Initiative’ in an effort to resolve long-standing questions on parasite biology, epidemiology, treatment, and host-parasite interactions [6,1]. Despite the clinical variation of giardiasis in active trophozoite infections, giardiasis does not cause overt inflammation of the intestinal epithelium [8] except in cases of prolonged disease [9]. Much work has been done to identify the underlying cause(s) of symptom variation, including parasite load [10], Giardia assemblage associated with the infection [11,12], antigenic variation in the parasite [13], infectious dose [14], and host immune status [9]. It is thought that a multitude of factors lead to the clinical manifestations of the disease
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