Bioscience Methods 2024, Vol.15, No.6, 302-314 http://bioscipublisher.com/index.php/bm 303 earwig biology but also provide broader insights into the evolution and function of innate immunity in invertebrates. This study aims to uncover novel aspects of earwig defense mechanisms that could have implications for pest control and the development of new antimicrobial strategies. 2 Earwig Immune System Components 2.1 Immune cells and organs in earwigs The immune system of earwigs, like other insects, comprises both cellular and humoral components. The primary immune cells involved are haemocytes, which play crucial roles in various immune responses such as phagocytosis, nodulation, and encapsulation. These cells are essential for limiting pathogen movement and replication within the insect body (Eleftherianos et al., 2021a). Additionally, the fat body, analogous to the liver in vertebrates, is a significant organ in the humoral immune response, producing antimicrobial peptides that are secreted into the hemolymph to combat infections (Eleftherianos et al., 2021b). 2.2 Role of pattern recognition receptors (PRRs) in pathogen detection Pattern recognition receptors (PRRs) are critical for the detection of pathogens in earwigs. These receptors identify pathogen-associated molecular patterns (PAMPs), which are conserved molecular signatures found on pathogens. The recognition of PAMPs by PRRs triggers the activation of various immune responses. In insects, PRRs such as Toll-like receptors and other signaling molecules are involved in initiating immune responses against bacterial, fungal, and viral infections (Smith et al., 2019). The activation of these receptors leads to the production of antimicrobial peptides and other defensive molecules that help in neutralizing the pathogens (Yu et al., 2022). 2.3 Signaling pathways involved in immune response Several signaling pathways are involved in the immune response of earwigs. The Toll pathway, Imd pathway, JNK pathway, and JAK/STAT pathway are some of the key signaling mechanisms that regulate the immune responses in insects (Figure 1). These pathways coordinate the production of antimicrobial peptides and other immune effectors in response to pathogen detection (Romo et al., 2016). The Toll pathway, for instance, is primarily activated by fungal and Gram-positive bacterial infections, leading to the production of specific antimicrobial peptides. The Imd pathway, on the other hand, is activated by Gram-negative bacterial infections and also results in the production of antimicrobial peptides. Additionally, the phenoloxidase (PO) cascade is another crucial component of the insect immune system, involved in melanization and the production of reactive intermediates that are toxic to pathogens (González-Santoyo and Córdoba‐Aguilar, 2012). The study of Yu et al. (2022) illustrates the complex interaction between key immune pathways in Drosophila's innate immunity system, specifically the Toll, Imd, JNK, and JAK/STAT pathways. These pathways are shown to regulate immune responses such as antimicrobial peptide production, melanization, cell proliferation, and apoptosis. The final immunological functions, ranging from antimicrobial defense to anti-tumor activity and wound healing, highlight the broad protective roles of these pathways. This detailed network underscores the sophisticated nature of immune regulation and its various physiological impacts in Drosophila. By understanding these components and mechanisms, we can gain insights into the complex and efficient immune system of earwigs, which allows them to effectively defend against a wide range of pathogens. 3 Antimicrobial Peptides (AMPs) 3.1 Types of AMPs identified in earwigs Antimicrobial peptides (AMPs) are a diverse group of molecules that play a crucial role in the innate immune system of earwigs. These peptides are typically short, cationic, and AMPhipathic, allowing them to interact with microbial membranes effectively. In earwigs, several types of AMPs have been identified, including defensins, cecropins, and attacins. Defensins are characterized by their cysteine-stabilized α/β structure, while cecropins are linear peptides known for their potent antibacterial activity. Attacins, on the other hand, are glycine-rich peptides that exhibit a broad spectrum of antimicrobial properties (Ageitos et al., 2017; Stączek et al., 2023).
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