Hemocytes: Central drivers of antimicrobial peptide expression and immune proteins in both cellular and humoral responses of Galleria mellonella

Insects have an effective innate immune system that includes both cellular and humoral responses for defense against pathogens. Antimicrobial peptides like gallerimycin and galiomycin, as well as immune proteins like hemolin, are the important effectors of the humoral immune response in Galleria mellonella L. (Lepidoptera:Pyralidae). Encapsulation, on the contrary, is one of the important cellular immune responses. This study investigated the tissue-specific expression of an immune effector in G. mellonella larvae after injection with Candida albicans (C.P. Robin) (Ascomycota: Debaryomycetaceae) and silica beads. The gene expression of gallerimycin, galiomycin, and hemolin was examined in total larvae, hemocytes, and fat bodies at 4 and 24 h following injection. Our findings indicate that hemocytes serve as the main site for AMP synthesis, especially after bead injection, implying a more effective immune recognition mechanism relative to pathogen injection. Furthermore, we detected higher hemolin expression in hemocytes than fat tissue, indicating its role in hemocyte-mediated immune responses. Encapsulation rates were also evaluated in bead-injected larvae. At 4 h post-injection, most beads were weakly encapsulated, whereas by 24 h, the majority were strongly encapsulated, reflecting a time-dependent maturation of the immune response. These results show that G. mellonella has a unique immune system, with hemocytes playing a key role in regulating AMP production and immune responses during infection. This study provides deeper insights into the molecular and cellular mechanisms of insect immunity, positioning G. mellonella as a valuable model for studying host–pathogen interactions.