Abstract
Invertebrates rely heavily on immune-like molecules with highly diversified variability so as to counteract infections. However, the mechanisms and the relationship between this variability and functionalities are not well understood. Here, we showed that the C-terminal domain of hemocyanin (HMC) from shrimp Litopenaeus vannamei contained an evolutionary conserved domain with highly variable genetic sequence, which is structurally homologous to immunoglobulin (Ig). This domain is responsible for recognizing and binding to bacteria or red blood cells, initiating agglutination and hemolysis. Furthermore, when HMC is separated into three fractions using anti-human IgM, IgG, or IgA, the subpopulation, which reacted with anti-human IgM (HMC-M), showed the most significant antimicrobial activity. The high potency of HMC-M is a consequence of glycosylation, as it contains high abundance of α-d-mannose relative to α-d-glucose and N-acetyl-d-galactosamine. Thus, the removal of these glycans abolished the antimicrobial activity of HMC-M. Our results present a comprehensive investigation of the role of HMC in fighting against infections through genetic variability and epigenetic modification.
Highlights
One of the major goals of comparative immunobiology is to identify molecules, which function in non-self recognition in invertebrates [1]
We further demonstrated the antimicrobial activity of HMC-M in other bacterial pathogens such as V. harveyi, V. fluvialis, V. anguillarum, A. hydrophila, A. sobria, and S. aureus
Progress has been made in recent years, with reports on the identification of homology of critical complement components and the opsonic defense mechanism in the Precambrian ancestor of bilateral animals and a cephalochordate of a basal lineage of chordate [18, 59, 60]
Summary
One of the major goals of comparative immunobiology is to identify molecules, which function in non-self recognition in invertebrates [1]. Invertebrates do not possess lymphocytes or antibodybased humoral immune response that plays a vital role in vertebrate immunity, yet they are capable of mounting effective immune responses, called innate immunity [2, 3]. Unlike adaptive immunity, which is only found in vertebrates, innate immunity is found in all animals with and without adaptive immunity. The innate immune system relies on its capability to rapidly detect pathogenassociated molecular patterns (PAMPs) of invading pathogenic microbes as foreign intruders for elimination [4,5,6]. This detection system is mainly based on pattern recognition receptors (PRRs). Several families of PRRs have been described, including the Toll-like receptors (TLRs)
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