Scientific Abstract

Proposal No.  IBD-0107R2
Principal Investigator:  Balakrishnan S. Ramakrishna, M.D., Ph.D.
Applicant Organization:  Christian Medical College Vellore Association (India)
Project Title:  Is the increasing incidence of Crohn's disease in a low prevalence area associated with reduced exposure to infection with helminths?
Period of Award:  March 1, 2005 – February 28, 2007

Crohn's disease is a disease in which defective innate immune recognition of intestinal microorganisms is believed to result in uncontrolled intestinal inflammation.  Conditioning of the immune system may prevent the mucosal inflammation characteristic of Crohn's disease.  Helminth parasites are known to induce a strong Th2 type immune response in the infected host.

The hypothesis to be tested is that infection with hookworm (the most common gastrointestinal helminth parasite infection worldwide) protects against the development of Crohn's disease, a disease characterized by a predominant Th1 type immune response.  We propose to test this hypothesis in southern India, where an apparent increase in the incidence of Crohn's disease is accompanied with a steeply falling prevalence of hookworm infection. 

Exposure to hookworms will be determined in patients with Crohn's disease diagnosed within the past two years, in patients with ulcerative colitis diagnosed within the past two years, and in unrelated healthy matched controls without gastrointestinal symptoms.  It is proposed to include a total of 91 subjects in each study group.  Peripheral blood mononuclear cells from all subjects will be cultured with crude and recombinant hookworm antigens and with phytohemagglutinin (non-specific stimulus for T cells) and output of three cytokines - interferon-γ, interleukin-4 and interleukin-10 - into the medium will be measured.  Lymphocyte activation and intracellular cytokine secretion in response to exposure to individual hookworm antigens will be assessed using three color flow cytometry, and subjects in the study groups classified as positive or negative for activation based on values from hookworm-free south Indian controls.  A Fisher’s exact test will be used to examine the association between infection (positive lymphocyte activation in response to hookworm antigens) and the diagnosis of Crohn's disease, and will be performed separately against each control group.  Associations between nature of lymphocyte cytokine responses to hookworm antigens (no response, interferon-γ, interleukin-4, interleukin-10 or combinations of the three) and the diagnosis of Crohn’s disease will similarly be examined.  The effect of possible confounders will be examined using logistic regression.  The absolute cytokine output in the three study groups will be compared using parametric or non-parametric tests as appropriate.

The results of these studies should allow the detection of possible negative associations of Crohn's disease with hookworm infections.  This is a relatively unexplored area, and there is as yet no direct evidence of the hypothesis elaborated above.  If negative associations are found, this would direct future research to identify molecules in hookworm which are responsible for conditioning the mucosal immune system to prevent mucosal inflammation.  Potentially, this could lead to novel therapies for the management or prevention of Crohn's disease.