Host responses to intestinal nematodes

Abstract

Helminth infection remains common in developing countries, where residents who suffer from the consequences of such infections can develop serious physical and mental disorders and often persist in the face of serious economic problems. Intestinal nematode infection induces the development of T_h2-type immune responses including the B cell IgE response; additionally, this infection induces an increase in the numbers and activation of various types of effector cells, such as mast cells, eosinophils and basophils, as well as the induction of goblet cell hyperplasia, antimicrobial peptide production and smooth muscle contraction, all of which contribute to expel nematodes. Innate immunity is important in efforts to eliminate helminth infection; cytokines, including IL-25, IL-33 and thymic stromal lymphopoietin, which are products of epithelial cells and mast cells, induce T_h2 cells and group 2 innate lymphoid cells to proliferate and produce T_h2 cytokines. Nematodes also facilitate chronic infection by suppression of immune reactions through an increased number of regulatory T cells. Immunosuppression by parasite infection may ultimately be beneficial for the host animals; indeed, a negative correlation has been found between parasite infection and the prevalence of inflammatory disease in humans.