Immune modulation by helminth parasites is instrumental in their success, blocking protective immunity to ensure their survival. Immunomodulation also “spills over” to impact many other immune responses to “bystander” antigens that may otherwise be the targets of allergic reactions (to environmental substances), autoimmune diseases (to self antigens), and inflammatory bowel disease (to commensal bacteria). These findings have given rise to the “Hygiene Hypothesis” that posits immune dampening (originally by bacteria, but broadened to include helminths) protect from untoward immune reactivity. However, there is evidence that helminth infections can also compromise responses to vaccines.
The most intensively-studied model systems for helminth immune modulation are Heligmosomoides polygyrus and Schistosoma mansoni, as detailed on other pages.