LAUSR

Abstract Hemolin is an immunoglobulin-like peptide that plays crucial role in microbial pathogen surveillance. However, its specific molecular actions in immune responses remain largely unclear. This study focused on the modulation of hemocyte phagocytosis of hemolin via its opsonin activity. A full length open reading frame (ORF) of hemolin (SeHem) was identified in the beet armyworm, Spodoptera exigua. Its ORF encoded 418 amino acids and shared 37.3–93.3% sequence similarities with other lepidopteran hemolins. SeHem was expressed in all developmental stages of S. exigua. In larval stage, SeHem was mostly expressed in hemocytes. Immune challenge significantly increased SeHem expression in hemocytes, fat body, midgut, and epidermis. RNA interference (RNAi) was performed by injecting SeHem-specific double-stranded RNA (dsRNA) into hemocoel, resulting in 60–80% reduction of SeHem transcript levels at 24–48 h after injection. Under RNAi condition, larvae showed significant loss of phagocytotic activities. In addition, hemocytes collected from control larvae exhibited significant reduction in phagocytosis when they were overlaid with plasma obtained from RNAi-treated larvae. RNAi treatment also suppressed encapsulation against injected beads. Furthermore, RNAi-treated larvae became highly susceptible to entomopathogenic bacteria. These results suggest that hemolin can act as opsonin in cellular immune responses to protect S. exigua against infections by entomopathogens.