Evolutionary adaptation of helminth immunomodulators to their hosts

Background: Parasitic nematodes have evolved secreted effector proteins which interact with host molecules to modulate the host immune response. These interactions can be highly specific and are under strong selective pressure. Here, we investigate the host-pathogen interaction between Heligmosomoides bakeri and its natural host Mus musculus, and between H. polygyrus and its natural host Apodemus sylvaticus. We focus on the Alarmin Release Inhibitor family (previously called HpARI) produced by heligmosomid parasites, which interact with IL-33 and heparan sulphate. Results: Using comparative genomics, we identified duplications and diversifications of the ARI family including multiple copies of ARI1 and conserved ARI3 homologues in both H. bakeri and H. polygyrus. We identify a new family member, HpolARI4, encoded by H. polygyrus, as well as a more distant homologue, HmixARI, encoded by Heligmosomum mixtum, a parasite of the bank vole (Myodes glareolus). Our functional assays identify that HpolARI4 preferentially blocks A. sylvaticus IL-33 but has little activity against M. musculus IL-33, whereas HbakARI2 is highly specific for M. musculus IL-33. We furthermore show differential interaction with host heparan sulphate, with HbakARI2 and HpolARI4 showing high affinity binding, whereas HbakARI3 shows no binding. We further test this family against non-host human IL-33 and show that functional suppression can be achieved by HbakARI3 in vitro and in vivo. Conclusion: By integrating genomic data, structural insights, and functional assays, we reveal how the expansion and diversification of the ARI family drive host-specific IL-33 modulation, providing a molecular model for nematode-host co-evolution.