:Giardia lamblia is a protozoan parasite which replicates in the small intestine of many species of mammals, and infections with G. lamblia are one of the most common human infections in the word. Most infections are self-limiting and acquired immune responses are essential for controlling G. lamblia infections in humans and other host species. Understanding the immune response to G. lamblia is therefore essential for better control of this disease. We have recently shown that B cell, gamma-delta T cell, IL-4 and IFN-gamma deficient mice can control acute infections with G. lamblia. In contrast, CD4+, alpha-beta T cells are required to control infections. Thus, a T cell-dependent, but antibody-independent. mechanism exists which can control G. lamblia. We have also shown that mast cell-deficient mice and IL-6 deficient mice cannot control G. lamblia infections. Also, in vitro studies have shown that nitric oxide and anti-microbial peptides known as defensins can inhibit G. lamblia. Based on these findings, the following hypothesis has been formulated: CD4+ T cells activate mast cells to produce IL-6 during G. lamblia infections. IL-6 production then leads to epithelial cell production of nitric oxide and defensins that control acute G. lamblia infections. We will test this hypothesis with the following specific aims: 1.To determine the importance of IL-6 production during G. lamblia infections. We will confirm the importance of IL-6 by treating immnunodeficjent mice with recombinant IL-6 during infections. IL-6 production will also be measured in vivo during infections in wild type and immunodeficient mice using RT-PCR. 2. To determine the importance of mast cell IL-6 production during G. lamblia infections. We will confirm the role of mast cells during infections by measuring mast cell responses during infections, by immuno-depletion of mast cells, and by reconstitution of mast cell deficient mice. We will examine mast cell production of IL-6 using immunohistochemistry and adoptive transfers. 3. To determine the mechanism of mast cell activation during G. lamblia infections. We will examine cytokine production by T cells in vivo and in vitro. We will also examine infections in cytokine deficient mice. We will examine intestinal epithelial cell (IEC) production of stem cell factor in vitro and in vivo. 4. To determine the mechanisms by which IL-6 production leads to control of acute G. lamblia infections. We will examine production of defensins and nitric oxide by IEC in vivo using RT-PCR and in vitro by Northern blots and biochemistry. Mice deficient in defensin expression and nitric oxide production will then be infected to determine their importance in controlling infections. Successful completion of these experiments will give us insights into immunity to G. lamblia, as well as developing this organism as a model system for understanding mucosal immune responses.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI049565-02
Application #
6621929
Study Section
Tropical Medicine and Parasitology Study Section (TMP)
Program Officer
Wali, Tonu M
Project Start
2002-02-01
Project End
2007-01-31
Budget Start
2003-02-01
Budget End
2004-01-31
Support Year
2
Fiscal Year
2003
Total Cost
$271,600
Indirect Cost
Name
Georgetown University
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
049515844
City
Washington
State
DC
Country
United States
Zip Code
20057
Li, Erqiu; Tako, Ernest A; Singer, Steven M (2016) Complement Activation by Giardia duodenalis Parasites through the Lectin Pathway Contributes to Mast Cell Responses and Parasite Control. Infect Immun 84:1092-1099
Tako, Ernest A; Hassimi, Maryam F; Li, Erqiu et al. (2013) Transcriptomic analysis of the host response to Giardia duodenalis infection reveals redundant mechanisms for parasite control. MBio 4:e00660-13
Kamda, Joel D; Nash, Theodore E; Singer, Steven M (2012) Giardia duodenalis: dendritic cell defects in IL-6 deficient mice contribute to susceptibility to intestinal infection. Exp Parasitol 130:288-91
Solaymani-Mohammadi, Shahram; Singer, Steven M (2010) Giardia duodenalis: the double-edged sword of immune responses in giardiasis. Exp Parasitol 126:292-7
Kamda, Joel Désiré; Singer, Steven M (2009) Phosphoinositide 3-kinase-dependent inhibition of dendritic cell interleukin-12 production by Giardia lamblia. Infect Immun 77:685-93
Li, Erqiu; Zhao, Aiping; Shea-Donohue, Terez et al. (2007) Mast cell-mediated changes in smooth muscle contractility during mouse giardiasis. Infect Immun 75:4514-8
Zhou, P; Li, E; Shea-Donohue, T et al. (2007) Tumour necrosis factor alpha contributes to protection against Giardia lamblia infection in mice. Parasite Immunol 29:367-74
Li, Erqiu; Zhou, Ping; Singer, Steven M (2006) Neuronal nitric oxide synthase is necessary for elimination of Giardia lamblia infections in mice. J Immunol 176:516-21
Li, Erqiu; Zhou, Ping; Petrin, Ziva et al. (2004) Mast cell-dependent control of Giardia lamblia infections in mice. Infect Immun 72:6642-9
Zhou, Ping; Li, Erqiu; Zhu, Nannan et al. (2003) Role of interleukin-6 in the control of acute and chronic Giardia lamblia infections in mice. Infect Immun 71:1566-8