Immune Regulation during Helminth Infections

Helminth is a nonphylogenetic term that refers to multicellular animals (or metazoans) that have adopted a parasitic lifestyle in mammalian hosts. They are more commonly referred to as parasitic worms. These worms generally (with the exception of Strongyloides stercoralis) cannot replicate within the host, and they have evolved distinct methods to co-exist with their host through the activation of an immune regulatory network. Until quite recently in human history, the majority of Homo sapiens were likely colonized by one type of worm or another, just like many mammals are in the wild. This close relationship has led to the evolution of ‘‘disease tolerance’’ by the host [1,2], in the presence of these parasites [3]. In other words, the mammalian host has evolved mechanisms to minimize the virulence of helminths, even without necessarily reducing worm burden. While helminths cause disease in hundreds of millions of people [4], nonetheless a large proportion of infected individuals are relatively tolerant to colonization with helminths.