Human helminth therapy to treat inflammatory disorders - where do we stand?

Parasitic helminths have evolved together with the mammalian immune system over many millennia and as such they have become remarkably efficient modulators in order to promote their own survival. Their ability to alter and/or suppress immune responses could be beneficial to the host by helping control excessive inflammatory responses and animal models and pre-clinical trials have all suggested a beneficial effect of helminth infections on inflammatory bowel conditions, MS, asthma and atopy. Thus, helminth therapy has been suggested as a possible treatment method for autoimmune and other inflammatory disorders in humans

Characterising the Mucosal and Systemic Immune Responses to Experimental Human Hookworm Infection

The mucosal cytokine response of healthy humans to parasitic helminths has never been reported. We investigated the systemic and mucosal cytokine responses to hookworm infection in experimentally infected, previously hookworm naive individuals from non-endemic areas. We collected both peripheral blood and duodenal biopsies to assess the systemic immune response, as well as the response at the site of adult worm establishment. Our results show that experimental hookworm infection leads to a strong systemic and mucosal Th2 (IL-4, IL-5, IL-9 and IL-13) and regulatory (IL-10 and TGF-β) response, with some evidence of a Th1 (IFN-γ and IL-2) response. Despite upregulation after patency of both IL-15 and ALDH1A2, a known Th17-inducing combination in inflammatory diseases, we saw no evidence of a Th17 (IL-17) response. Moreover, we observed strong suppression of mucosal IL-23 and upregulation of IL-22 during established hookworm infection, suggesting a potential mechanism by which Th17 responses are suppressed, and highlighting the potential that hookworms and their secreted proteins offer as therapeutics for human inflammatory diseases

Suppression of inflammatory immune responses in celiac disease by experimental hookworm infection

We present immunological data from two clinical trials where the effect of experimental human hookworm (Necator americanus) infection on the pathology of celiac disease was evaluated. We found that basal production of Interferon- (IFN-)γ and Interleukin- (IL-)17A from duodenal biopsy culture was suppressed in hookworm-infected participants compared to uninfected controls. Increased levels of CD4+CD25+Foxp3+ cells in the circulation and mucosa are associated with active celiac disease. We show that this accumulation also occurs during a short-term (1 week) oral gluten challenge, and that hookworm infection suppressed the increase of circulating CD4+CD25+Foxp3+ cells during this challenge period. When duodenal biopsies from hookworm-infected participants were restimulated with the immunodominant gliadin peptide QE65, robust production of IL-2, IFN-γ and IL-17A was detected, even prior to gluten challenge while participants were strictly adhering to a gluten-free diet. Intriguingly, IL-5 was produced only after hookworm infection in response to QE65. Thus we hypothesise that hookworm-induced TH2 and IL-10 cross-regulation of the TH1/TH17 inflammatory response may be responsible for the suppression of these responses during experimental hookworm infection

Hookworm excretory/secretory products induce interleukin-4 (IL-4)+ IL-10+ CD4+ T cell responses and suppress pathology in a mouse model of colitis

Evidence from human studies and mouse models shows that infection with parasitic helminths has a suppressive effect on the pathogenesis of some inflammatory diseases. Recently, we and others have shown that some of the suppressive effects of hookworms reside in their excretory/secretory (ES) products. Here, we demonstrate that ES products of the hookworm Ancylostoma caninum (AcES) suppress intestinal pathology in a model of chemically induced colitis. This suppression was associated with potent induction of a type 2 cytokine response characterized by coexpression of interleukin-4 (IL-4) and IL-10 by CD4+ T cells, downregulation of proinflammatory cytokine expression in the draining lymph nodes and the colon, and recruitment of alternatively activated (M2) macrophages and eosinophils to the site of ES administration. Protease digestion and heat denaturation of AcES resulted in impaired induction of CD4+ IL-4+ IL-10+ cell responses and diminished ability to suppress colitis, indicating that protein component(s) are responsible for some of the immunosuppressive effects of AcES. Identification of the specific parasite-derived molecules responsible for reducing pathology during chemically induced colitis could lead to the development of novel therapeutics for the treatment of human inflammatory bowel disease