The plasma factor Immulectin ‐5 of Ostrinia furnacalis mediates the hemocytic encapsulation against parasitic wasp larvae by facilitating nonself recognition

BACKGROUND: Successful endoparasitism requires parasitoids to overcome the host immune defense, encapsulation. However, the mechanisms governing encapsulation, particularly its initiation, remain poorly understood, limiting our understanding of coevolution between parasitoids and their hosts and constraining the broader application of parasitoids in biological control. RESULTS: Our results showed that Ostrinia furnacalis plasma factor Immulectin-5 (IML-5) is essential for nonself recognition of hemocytic-mediated encapsulation of Macrocentrus cingulum larvae. Upon incubation with host plasma, three OfIMLs specifically bound to the wasp larval surface. Among them, OfIML-5, predominantly expressed in the fat body, was secreted into the plasma and strongly upregulated upon wasp larval exposure. RNAi-mediated knockdown or antibody-mediated neutralization of OfIML-5 significantly impaired host encapsulation ability. Consistently, CRISPR/Cas9 knockout of OfIML-5 decreased the encapsulation rate from 73.5% to 17.9%. Furthermore, OfIML-5 simultaneously binds to the surface of wasp larvae and hemocytes, suggesting that it possibly acts as a recognition factor and adaptor to promote hemocytic encapsulation. Co-immunoprecipitation assays indicated that OfIML-5 interacts with OfIML-3 and may participate in the transduction of nonself signals. Finally, we provide preliminary evidence that miR-34-5p secreted by M. cingulum targets the OfIML-5 gene and suppresses its expression, thereby attenuating host encapsulation. CONCLUSION: Our results indicate that OfIML-5 interacts with OfIML-3 and may function to transmit nonself signals to hemocytes, thereby promoting encapsulation against parasitoid wasp. Meanwhile, parasitic wasp M. cingulum secretes miR-34-5p, which targets OfIML-5 and suppresses host encapsulation. These findings help clarify the intricate immune interaction strategies between parasitoid wasps and their hosts.