page_title: Effects of parasitic worms on the immune system
section_title: Mechanisms of immune regulation
hierarchical_section_title: Effects of parasitic worms on the immune system / Immune response hypothesis / Mechanisms of immune regulation
caption_attribution_description: T helper cell function
context_page_description: The effects of parasitic worms, or helminths, on the immune system is a recently emerging topic of study among immunologists and other biologists. Experiments have involved a wide range of parasites, diseases, and hosts. The effects on humans have been of special interest. The tendency of many parasitic worms to pacify the host's immune response allows them to mollify some diseases, while worsening others.
context_section_description: Extensive research shows that parasitic worms have the ability to deactivate certain immune system cells, leading to a gentler immune response.  Often, such a response is beneficial to both parasite and host, according to Professor of Medical Microbiology Graham Rook of University College London.  This immune "relaxation" is incorporated throughout the immune system, decreasing immune responses against harmless allergens, gut flora, and the body itself.
  In the past, helminths were thought to simply suppress T-helper Type 1 (Th1) cells while inducing T-helper Type 2 (Th2) cells.  Rook points out that this hypothesis would only explain the regulatory effects of parasitic worms on autoimmune diseases caused by Th1 cells.  However, helminths also regulate Th2-caused diseases, such as allergy and asthma.  Professor Rook postulates that different parasitic worms suppress different Th types, but always in favor of regulatory T (Treg) cells.
  Professor Rook explains that these regulatory T cells release interleukins that fight inflammation.  In the Journal of Biomedicine and Biotechnology, Dr. Osada et al. note that macrophages induced by Treg cells fight not only the parasitic disease, but also resist the immune system's response to allergens and the body.  According to Dr. Hopkin, the author of a 2009 Parasite Immunology article on asthma and parasitic worms, other immunoregulatory mechanisms are also activated, including Mast cells, eosinophils, and cytokines that invoke a strong immunoglobulin E (IgE) response.  All these fight a hyperactive immune response, reduce the inflammation throughout the body, and thus lead to less severe autoimmune diseases.
  Dr. Osada et al. state that because parasitic worms may and often do consist of allergens themselves, the degree to which they pacify or agitate the immune response against allergens is a balance of their regulating effects and their allergenic components.  Therefore, depending on both of these variables, some parasitic worms may worsen allergies.
  In their Parasite Immunology article on worms and viral infections, Dr. Kamal et al. explain why some parasitic worms aggravate the immune response.  Because parasitic worms often induce Th2 cells and lead to suppressed Th1 cells, problems arise when Th1 cells are needed.  Such cases occur with viral diseases.  Several examples of viral infections worsened by parasitic worms are described below.
caption: Importance of T helper cells in an immune response: T helper cells recognize antigens from antigen-presenting cells (APCs) and then release cytokines and activate other immune cells.  Parasitic worms influence what kinds of T helper cells are activated.
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