Geohelminth infections: impact on allergic diseases

Dominance of P-glycoprotein 12 in phenotypic resistance conversion against ivermectin in Caenorhabditis elegans

While diseases caused by nematodes remains a considerable drawback for the livestock, agriculture and public health, anthelmintics drug resistance has been observed over the past years and is a major concern for parasite control. Ivermectin, initially considered as a highly potent drug, currently presents a reduced anti-helminthic efficacy, which is influenced by expression of several ATP-binding cassette transporters (ABC), among them the P-glycoproteins (Pgps). Here we present some evidences of Pgps dominance during Ivermectin resistance/susceptibility using Pgps double silencing in C. elegans and the phylogenetic relationship of Pgps among nematodes, which strengthen the use of this model for study of drug resistance in nematodes. Firstly, we evaluated the quantitative gene expression of 12 out the 15 known Pgps from resistant and WT strains of C. elegans, we demonstrated the upregulation of Pgps 12 and 13 and downregulation of all remaining Pgps in ivermectin resistant strain. By using an RNAi loss-of-function approach we observed that Pgp 12 gene silencing reverts the resistance phenotype to ivermectin, while Pgp 4 gene silencing does not alter the resistance phenotype but induces a resistance in wild type strain. Interestingly, the dual silencing of Pgp 12 and Pgp 4 expression demonstrates the dominance of phenotype promoted by Pgp 12 silencing. Finally, in silico analysis reveals a close relationship between Pgps from C. elegans and several nematodes parasites. Taken together, our results indicate that Pgp 12 is crucial for the resistance to ivermectin and thus a good candidate for further studies aiming to develop specific inhibitors to this transporter, allowing the continuous use of ivermectin to control the burden on animal and human health inflicted by nematode parasites globally.

Parasites and asthma

Nowadays, many studies have found low morbidity of asthma in epidemic areas of parasitic diseases, as shown by the hygiene hypothesis. It is obvious that some parasite infections can prevent asthma and studies have been carried out to clarify the mechanism of the preventive effect and search for the future asthmatic therapies. Previous findings have indicated that this mechanism may be related to the immune response switching from Th1 to Th2 and important cells induced by parasites, including the regulatory T cells, regulatory B cells, dendrite cells, and alternatively activated macrophages. Cytokine IL-10 also plays a nonredundant role in protection against allergic airway inflammation in asthma. This review focuses on the relationship between parasites and asthma, and the potential protection mechanism involved.

Toxocara canis and the allergic process

The protective effect of infectious agents against allergic reactions has been thoroughly investigated. Current studies have demonstrated the ability of some helminths to modulate the immune response of infected hosts. The objective of the present study was to investigate the relationship between Toxocara canis infection and the development of an allergic response in mice immunised with ovalbumin (OVA). We determined the total and differential blood and bronchoalveolar lavage fluid cells using BALB/c mice as a model. To this end, the levels of interleukin (IL)-4, IL-5 and IL-10 and anti-OVA-IgE were measured using an ELISA. The inflammatory process in the lungs was observed using histology slides stained with haematoxylin and eosin. The results showed an increase in the total number of leukocytes and eosinophils in the blood of infected and immunised animals at 18 days after infection. We observed a slight lymphocytic inflammatory infiltrate in the portal space in all infected mice. Anti-OVA-IgE levels were detected in smaller proportions in the plasma of immunised and infected mice compared with mice that were only infected. Therefore, we concluded that T. canis potentiates inflammation in the lungs in response to OVA, although anti-OVA-IgE levels suggest a potential reduction of the inflammatory process through this mechanism.

Overweight, asthma symptoms, atopy and pulmonary function in children of 4-12 years of age: findings from the SCAALA cohort in Salvador, Bahia, Brazil

OBJECTIVE

To evaluate the association between overweight and the occurrence of asthma and atopy in a cohort of children of 4-12 years of age living in the city of Salvador in 2005.

DESIGN

Cross-sectional study nested in a cohort.

SETTING

The metropolitan region of Salvador, Bahia, Brazil.

SUBJECTS

The study included 1129 children of 4-12 years age who presented complete information on the variables used here. Skin tests for allergy, spirometry, faecal parasitology, serum IgE and anthropometric surveys were conducted. Poisson's multivariate regression was adopted.

RESULTS

Wheezing was found in 29·1% and asthma in 22·8% of children, both conditions being more common in those under 6 years of age and 34% more common in overweight children (prevalence ratio (PR) = 1·34; 95% CI 1·07, 1·67) following adjustment. The ratio between forced expiratory volume in 1s and forced vital capacity was associated with overweight (PR = 1·35; 95% CI 1·11, 1·61). No statistically significant association was found between overweight and allergen-specific IgE or with wheezing.

CONCLUSIONS

These results are in agreement with the hypothesis that overweight is associated with asthma and pulmonary function, even following adjustment for intervening variables known to be associated with the pathogeny of asthma.

Understanding human-Plasmodium falciparum immune interactions uncovers the immunological role of worms

BACKGROUND

Former studies have pointed to a monocyte-dependent effect of antibodies in protection against malaria and thereby to cytophilic antibodies IgG1 and IgG3, which trigger monocyte receptors. Field investigations have further documented that a switch from non-cytophilic to cytophilic classes of antimalarial antibodies was associated with protection. The hypothesis that the non-cytophilic isotype imbalance could be related to concomittant helminthic infections was supported by several interventions and case-control studies.

METHODS AND FINDINGS

We investigated here the hypothesis that the delayed acquisition of immunity to malaria could be related to a worm-induced Th2 drive on antimalarial immune responses. IgG1 to IgG4 responses against 6 different parasite-derived antigens were analyzed in sera from 203 Senegalese children, half carrying intestinal worms, presenting 421 clinical malaria attacks over 51 months. Results show a significant correlation between the occurrence of malaria attacks, worm carriage (particularly that of hookworms) and a decrease in cytophilic IgG1 and IgG3 responses and an increase in non-cytophilic IgG4 response to the merozoite stage protein 3 (MSP3) vaccine candidate.

CONCLUSION

The results confirm the association with protection of anti-MSP3 cytophilic responses, confirm in one additional setting that worms increase malaria morbidity and show a Th2 worm-driven pattern of anti-malarial immune responses. They document why large anthelminthic mass treatments may be worth being assessed as malaria control policies.

Early infection with Trichuris trichiura and allergen skin test reactivity in later childhood

BACKGROUND

Allergic diseases cause a large and increasing burden in developed countries and in urban centres in middle-income countries. The causes of this increase are unknown and, currently, there are no interventions to prevent the development of allergic diseases. The 'hygiene hypothesis' has tried to explain the increase through a reduction in the frequency of childhood infections causing a failure to program the immune system for adequate immune regulation. Intestinal helminth parasites are prevalent in childhood in developing countries and are associated with a lower prevalence of allergen skin test reactivity and asthma.

OBJECTIVES

To investigate whether children who had intestinal helminth infections during early childhood have a lower prevalence of allergen skin test reactivity later in childhood.

METHODS

We re-visited a population of 1055 children from whom stool samples had been collected for detection of intestinal helminth infections for another study, and collected new stool samples and performed allergen skin prick testing. Information on potential confounding variables was collected.

RESULTS

Children with heavy infections with Trichuris trichiura in early childhood had a significantly reduced prevalence of allergen skin test reactivity in later childhood, even in the absence of T. trichiura infection at the time of skin testing in later childhood.

CONCLUSION

Early heavy infections with T. trichiura may protect against the development of allergen skin test reactivity in later childhood. Novel treatments to program immune-regulation in early childhood in a way that mimics the effects of early infections with T. trichiura may offer new strategies for the prevention of allergic disease.

Towards a differential definition of atopy: Anisakis simplex and the relationship between parasites and arthropods in respiratory allergy

Protective as well as enhancing effects of parasite infections on allergic disease have been postulated. Previous studies on this relationship focused frequently on skin test reactivity against aeroallergens, being house dust mites (HDM) the main agents responsible for a positive atopy outcome. We aimed to analyse the possible relationship between human parasite infection induced Anisakis simplex urticaria and respiratory allergy. A total of 86 patients with gastro-allergic Anisakiasis and 203 patients with chronic urticaria sensitized against A. simplex were studied for sensitization against aeroallergens and evaluated for rhinoconjunctivitis or bronchial asthma (RCBA). We compared the results with a control group of 250 consecutive patients referred for evaluation of allergic RCBA and atopy prevalence data of our region. Whereas no effect of A. simplex related disease on the overall allergic respiratory disease could be detected, a highly significant higher prevalence of RCBA associated HDM sensitization, but diminished allergy against other common aeroallergens (pollen, mould or dander) was observed in these groups. The relationship between A. simplex parasitism-associated acute or chronic urticaria on one side and allergic respiratory disease on the other side depends on the definition of atopy. We propose a differential definition of atopy, with a special emphasis on arthropod related sensitization.

Modulation of anaphylaxis by helminth-derived products in animal models

Helminths have a profound immunomodulatory effect upon the inductive and effector phases of inflammatory responses, including allergy. Several animal models of anaphylaxis have been established to investigate the mechanisms by which helminth infections or helminth-derived products interfere with the onset of allergic reactions. The focus of our studies was the immunosuppression induced by the intestinal roundworm Ascaris suum in the production of anaphylactic antibodies and the development of lung eosinophilic inflammation and hyperreactivity to its own allergens and to unrelated antigens. Thus, we identified a single protein affinity purified from the A. suum body extract, named PAS-1, which maintains all its immunosuppressive properties and promotes a significant increase in interleukin-10 production, an essential cytokine for the effectiveness of the suppressive mechanism. In addition, PAS-1 primes for regulatory T cells, which also mediate this mechanism. Therefore, this helminth molecule may be a promising target for therapeutic applications in allergic disorders.