Protozoan parasites and type I interferons: a cold case reopened

•Similarly to viruses, protozoan parasites can induce type I IFN in vitro and in vivo.•Parasites are recognized by innate immune receptors that also detect viruses.•IFN-α/β can be either host-protective or pathogenic during parasite infection.•IFN ‘crosstalk’ can influence disease outcome during parasite infection.

Protozoan parasites, such as Plasmodium, Toxoplasma, Cryptosporidium, trypanosomes, and Leishmania, are a major cause of disease in both humans and other animals, highlighting the need to understand the full spectrum of strategies used by the host immune system to sense and respond to parasite infection. Although type II interferon (IFN-γ) has long been recognized as an essential antiparasite immune effector, much less is known about the role of type I interferons (IFN-α and -β) in host defense, particularly in vivo. Recent studies are reviewed which collectively highlight that type I IFN can be induced in response to parasite infection and influence the outcome of infection.