The immune function of thioester-containing proteins in typical invertebrate disease vectors

Disease vectors, such as arthropods, primarily rely on innate immunity to counteract pathogen invasions, typically through the recognition and binding of pathogen-associated molecular patterns (PAMPs) by the host's pattern recognition receptors (PRRs). As a conserved immune effector gene family from insects to mammals, the complement system may play an essential role in combating pathogenic microorganisms. In arthropods, the complement proteins are often referred to as thioester-containing proteins (TEPs) because thioester motifs are one of the essential functional domains of the first proteins characterized within the C3 and A₂M family. TEPs mainly function as specialized PRRs in sensing and binding to pathogens or their components. This paper presents a comprehensive review of the common domain and functions of TEPs in major disease vectors, in particular the specific decision-making ones expressed by Arthropoda (medical arthropods) and Mollusca (Biomphalaria glabrata) after pathogen infections. The relationship between the structure and antibacterial/antiviral activities of TEPs would further our understandings on the mechanisms governing the initiation of innate immune responses in typical disease vectors.