C-type lectin interacting with β-integrin enhances hemocytic encapsulation in the cotton bollworm, Helicoverpa armigera.

The encapsulation reaction in invertebrates is analogous to granuloma formation in vertebrates, and this reaction is severely compromised when ecdysone signaling is blocked. However, the molecular mechanism of the encapsulation reaction, especially how ecdysone controls this process, remains obscure. In our previous study, we found that the C-type lectin HaCTL3 from the cotton bollworm Helicoverpa armigera might be involved in fighting against bacteria as a pattern recognition receptor (PRR). In the current study, we demonstrated that HaCTL3 is involved in defending against parasitism and directly binds to the surface of nematodes. In vitro and in vivo studies indicated that HaCTL3 enhanced hemocytic encapsulation and melanization. Confocal microscopy imaging showed that the H. armigera β-integrin (Haβ-integrin) was located on the surface of hemocytes and participated in encapsulation. By co-immunoprecipitation, we showed that HaCTL3 and Haβ-integrin interact, and knockdown of Haβ-integrin suppressed the hemocytic encapsulation towards HaCTL3-coated beads. These results suggest that Haβ-integrin serves as a hemocytic receptor of HaCTL3 during the encapsulation reaction. Furthermore, we demonstrated that 20-hydroxyecdysone (20E) treatment dramatically induced the expression of HaCTL3, and knockdown of the 20E receptor ecdysone receptor (EcR)/ultraspiracle (USP) exhibited opposite responses to 20E treatment. This study provides the first hemocytic receptor of the PRR during encapsulation in insects and will be beneficial for uncovering the molecular mechanisms of encapsulation, as well as its ecdysone control.