Effect of parasitosis on allergic sensitization in rats sensitized with ovalbumin: interaction between parasitosis and allergic sensitization

Worms as therapeutic agents for allergy and asthma: understanding why benefits in animal studies have not translated into clinical success

Helminth infections are associated with decreased rates of autoimmunity and allergy, and several clinical studies have demonstrated that intentional infection with helminths can reduce symptoms of autoimmune diseases. In contrast, though numerous animal studies have demonstrated that helminth infections ameliorate allergic diseases, clinical trials in humans have not shown benefit. In this article, we review in detail the 2 human studies that have prospectively tested whether helminth infections protect against allergy. We next review the research designs and results obtained from animal studies, and compare these to the human trials. We then postulate possible reasons for the lack of efficacy observed in clinical trials to date and discuss potential future areas of research in this field.

Helminth infection does not reduce risk for chronic inflammatory disease in a population-based cohort study

BACKGROUND & AIMS

Parasitic helminth infections can suppress symptoms of allergy, type 1 diabetes, arthritis, and inflammatory bowel disease in animal models. We analyzed data from a large, population-based cohort study to determine whether common childhood enterobiasis protects against these diseases.

METHODS

We collected information on individual prescriptions filled for the drug mebendazole against Enterobius vermicularis for all children born in Denmark 1995-2008 from the National Register of Medicinal Product Statistics (n = 924,749; age 0-14 years); 132,383 of these children (14%) filled a prescription for mebendazole, 102,482 of the children (11%) had a household peer who was registered with a filled mebendazole prescription, and the remaining 689,884 children (75%) comprised the reference group. Children diagnosed with asthma, type 1 diabetes, juvenile arthritis, ulcerative colitis, or Crohn's disease were identified from the National Patient Registry. We used Poisson regression to estimate confounder-adjusted incidence rate ratios for first in- or outpatient hospital diagnosis of chronic inflammatory disease according to history of mebendazole treatment prescribed to children in the study.

RESULTS

Chronic inflammatory disease was diagnosed in 10,352 children during 6.4 million person-years of follow-up. The incidence rate ratios was 1.07 for asthma (95% confidence interval [CI]: 1.00-1.13), 1.05 for type 1 diabetes (95% CI: 0.79-1.12), 1.13 for juvenile arthritis (95% CI: 0.94-1.37), 0.77 for ulcerative colitis (95% CI: 0.41-1.46), and 1.44 for Crohn's disease (95% CI: 0.82-2.53). Results were not modified by number of treatments or age at treatment.

CONCLUSIONS

Based on a population-based analysis, enterobiasis does not reduce risk for asthma, type 1 diabetes, arthritis, or inflammatory bowel disease.

Immunization of proteins from Toxascaris leonina adult worm inhibits allergic specific Th2 response

Recently, the influence of parasitic infections on the incidence of allergic diseases has become the focus of increased attention. In order to ascertain whether parasite-derived proteins could inhibit the allergic specific Th2 response, we applied excretory-secretory protein (Tl-ES) or total protein (Tl-TP) of the adult worm Toxascaris leonina to asthma model mice prior to or simultaneously with OVA challenge, after which we assessed the OVA-specific Th2 responses. The group subjected to immunization with Tl-ES and Tl-TP (immunized group) evidenced a thinning of the bronchial epithelial and muscle layer, a disruption and shedding of epithelial cells, a reduction in the number of goblet cells, and a reduction in mucus production as compared to the group treated with Tl-ES coupled with OVA challenge (challenge with OVA groups) and the OVA-induced asthma group. The administration of Tl-ES and Tl-TP, regardless of injection time, was shown to inhibit the recruitment of inflammatory cells into the airway, and in particular, macrophages, neutrophils, and lymphocytes were significantly reduced as the result of the parasite proteins. However, the total number of eosinophils was slightly reduced as the result of the administration of parasite proteins. Sensitization and OVA challenge was shown to accelerate the secretion of Th2 cytokines (IL-4 and IL-5) within the lung, but in the immunized groups, those levels were lower. The administration of Tl-TP and OVA challenge group also evidenced a significant reduction in IL-4 levels as compared to the OVA-challenged group. The concentrations of Th2 cytokines in the Tl-ES and OVA challenge group were more similar to those observed in the OVA-challenged group. The concentration of IL-10 and TGF-beta in the lung was decreased substantially in the OVA-only challenge group, but the Tl-TP immunized group exhibited significantly induced IL-10 cytokine. OVA-specific IgG2a, IgG1, and IgE levels in the immunized groups were significantly lower than those detected in the OVA-challenged group. In conclusion, parasite-derived protein is able to inhibit OVA-specific Th2 responses, and in particular, immunization with parasite proteins exerts a more profound protective effect than is seen with the treatment of allergic reactions. The results of our study are encouraging in terms of our further understanding of the molecular basis of immune evasion by nematodes.