Eosinophils are a type of white blood cell that resides in the circulation and helps fight parasitic infections by secreting toxic compounds. They are recruited to sites of parasite infection by signals from various T cell types including TH1, TH17, and TH2 cells as well as CD8 cytotoxic T cells. Recent research challenges the idea that only chordates have adaptive immune responses and antibody diversity, finding that many species use diverse methods to recognize antigens without antibodies.

1. Eosinophils are a subset of granulocytes that normally reside in the circulation. When activated,
these cells secrete toxic compounds that are a key component in the eradication of helminthic
parasite infections. Eosinophils are recruited to sites of parasite infections by: Interferon-gamma
produced by TH1 cells GM-CSF produced by TH1 and TH17 cells CCL20 produced by TH17
cells CCL11 produced by TH2 cells Interferon-gamma produced by CD8 cytotoxic T cells
Recent insights into adaptive immune responses in other phyla have highlighted that the ability
to elicit adaptive immune responses to diverse antigens is unique to chordates that the entire
animal kingdom uses identical methods to maintain antigen diversity that the evolution of
antibody diversity has led to chordates being superior to all other phyla that many other species
have evolved similar mechanisms to sense many diverse antigens