Immune surveillance on the insect body surface recognizes a pathogen-derived fungal protease to activate defenses
2026-05-09
Immune systems must distinguish between pathogens and commensals to mount effective responses. However, how hosts discriminate among fungi at surface barriers is largely unknown. Here, we report a surveillance mechanism on the locust body surface that couples general fungal recognition with pathogen-specific activation. The host immulectin-1 (IML1) binds surface-exposed fungal mannans, but immune activation requires cleavage by fungal protease SP28 to release bioactive peptide. The protease is found in most fungi, but high evolutionary divergence confers its host-specific activity. Disrupting the IML1-SP28 interaction, either by deleting fungal SP28 , silencing host IML1 , or blocking IML1 with excess mannan, abrogates immune responses and accelerates host mortality. This protease-gated checkpoint suggests an evolutionarily conserved principle in insect-fungal interactions, with potential implications for developing novel biopesticides and antifungal agents.