Aug 2026· Fish and Shellfish Immunology· pp.
111622
· 0 citations· 57 references
Medicine
Abstract
C-type lectins (CTLs) are vital pattern-recognition receptors (PRRs) that mediate innate immune responses in mollusks, yet their characterization in Caenogastropoda, the largest gastropod group, remains limited. This study characterizes LitCTL1, a novel secreted single-domain C-type lectin from the common periwinkle, Littorina littorea. The 199-amino acid polypeptide contains a conserved carbohydrate recognition domain with canonical QPD and WND motifs and is predicted to form a homodimer. Uniquely, LitCTL1 was localized in both circulating hemocytes and mucus-secreting epithelial cells of the foot, mantle, and hypobranchial gland - the first report of such dual localization for a molluscan lectin, linking systemic and mucosal defense. Expression analysis revealed that LitCTL1 is constitutively expressed in hemocytes. Functional assays with recombinant LitCTL1 demonstrated its role as a potent opsonin with hemagglutinating activity, significantly enhancing hemocyte spreading and the phagocytosis of zymosan. Genomic analysis reveals that LitCTL1 belongs to a rapidly diversifying, genus-specific expansion distinct from conserved perlucin-like lineages. These results identify LitCTL1 as a key effector molecule in both systemic and mucosal innate immunity, likely reflecting an evolutionary adaptation to the microbial challenges of the intertidal environment.
Results demonstrate that LvCTL functions as an important immune recognition molecule and contributes to antibacterial defense against V. parahaemolyticus in L. vannamei.
Ning Fu, Mengxin Xing, Yuyu Wang et al.· Fishes· 0 citations
C-type lectins (CTLs) are key pattern recognition receptors in invertebrate innate immunity, but the functions of clip domain-containing CTLs in crustaceans during infection by decapod iridescent virus 1 (DIV1) remain largely unknown. Here, we identified a novel clip domain-containing CTL, Mr-clip-CTL, from Macrobrachium rosenbergii. The gene encodes a protein containing an N-terminal clip domain and two C-terminal CRDs. Mr-clip-CTL shares 77.78% amino acid identity with M. nipponense CLIP-LEC and is predominantly expressed in the stomach. Following DIV1 infection, its expression was significantly upregulated in the stomach. Using RNAi-mediated knockdown, we found that Mr-clip-CTL knockdown significantly decreased DIV1 major capsid protein (MCP) expression, indicating a positive role. Conversely, knockdown of Mr-clip-CTL significantly increased antimicrobial peptides (AMPs) expression and phenoloxidase (PO) activity, implicating a possible negative regulatory role of this protein in these immune responses, although direct regulation remains to be established. In summary, this study identifies Mr-clip-CTL, a clip domain-containing CTL from M. rosenbergii, as a novel host factor that promotes DIV1 replication, with its pro-viral function correlated with altered AMP expression and PO activity. These findings provide a potential target for antiviral research in crustaceans and open avenues for mechanistic investigation.
Huan-Huan Qin, Wen-Qing Yan, Kong-Yan Zhu et al.· Fish and Shellfish Immunolog...· 0 citations
The human gut microbiota comprises more than 50% of Bacteroides species that produce small diffusible molecules like sphingolipids that play a key role in modulating the host’s immune responses. In particular, Bacteroides fragilis produces glycosphingolipids termed ‘BfaGCs’ that can activate type I Natural Killer T (NKT) cells. BfaGCs exhibit distinct structural characteristics, including truncated sphinganine chains, varied branching patterns, and specific functional groups, distinguishing them from the canonical type I NKT cell marker, α-galactosylceramide (KRN7000).
Using a combinatorial cellular immunology, mass spectrometry and X-ray crystallography approach, we provide the first insights into the molecular mechanism of recognition of four novel BfaGCs presented by the antigen-presenting molecule CD1d, in complex with the type I NKT TCR.
The co-culture assay performed with bone marrow-derived dendritic cells and NKT cells in the presence of specific BfaGCs indicated that branching in their sphinganine chain is a critical determinant of NKT cell activation. The three-dimensional complex structures revealed that the TCR adopted a parallel docking topology atop the F’-pocket of CD1d in recognising the presented BfaGCs, reminiscent of other published type I NKT TCR lipid complexes. Nevertheless, the terminal sphinganine branching of BfaGCs facilitates unique interactions within the CD1d F’-pocket, thereby underpinning their distinctive agonistic properties. Also, the NKT TCR demonstrates high binding affinities for both stimulatory and non-stimulatory forms of CD1d-presented BfaGCs, affirming BfaGCs as bona fide CD1d ligands that modulate host immune defences via NKT cells.
Thus, BfaGCs were demonstrated to function as immunomodulatory mediators influencing the host’s defence in the context of NKT cells. Collectively, our findings enhance understanding of the symbiotic interplay between lipid-producing gut microbes and the host.
Australian Research Council
Mucosal and Regional Immunology (MUC)
P. Thirunavukkarasu, Vasudha Maddali, Da-Jung Jung et al.· Journal of Immunology· 0 citations
T-cell receptor (TCR) signaling is essential for adaptive immunity in vertebrates, with the tyrosine kinases Fyn, Lck, and Zap-70 playing central roles in signal transduction. In the present study, the full cDNA sequences of Fyn, Lck, and Zap-70 from golden pompano (Trachinotus ovatus) were obtained by RT-PCR and RACE-PCR and their expression patterns in normal tissues and head kidney (HK) following lipopolysaccharide (LPS), polyinosinic-polycytidylic acid (polyI:C) stimulation and Vibrio alginolyticus infection were examined by qPCR. The open reading frames of trFyn, trLck, and trZap-70 respectively encoded 537, 513, and 609 amino acids, all containing conserved similar functional domains as their mammalian counterparts. qPCR analysis revealed that all three genes were ubiquitously expressed in examined tissues, with high expression in immune-related tissues. trFyn, trLck, and trZap-70 were significantly induced in HK after LPS, polyI:C stimulation and V. alginolyticus infection. Co-immunoprecipitation (co-IP) assay demonstrated that both trFyn and trLck could interact with trZap-70 in HEK-293T cells. These findings provide molecular basis for further study of the TCR signaling and T-cell mediated immunity in golden pompano.
You-Chuan Wei, Dongqiang Gan, Wen Qi et al.· Fish and Shellfish Immunolog...· 0 citations
Extracellular traps (ETs) are a novel host defense mechanism used to immobilize and eliminate invading microorganisms, and their formation depends on the recognition of foreign pathogens by membrane receptors. Previous studies have demonstrated that Vibrio splendidus flagellin can induce the release of ETs in coelomocytes of the sea cucumber Apostichopus japonicus, yet the underlying regulatory mechanism remains unclear. Here, we identify another Toll-like receptor (TLR) homolog, AjTLR2, in Apostichopus japonicus, which is composed of an extracellular LRR domain, a transmembrane domain, and an intracellular TIR domain. As a membrane receptor, AjTLR2 is upregulated upon infection with Vibrio splendidus AJ01, which is isolated from diseased Apostichopus japonicus. The extracellular LRR domain exhibits binding activity toward LPS, PGN, and MAN. In addition to these ligands, AjTLR2 recognizes flagellin C of AJ01 (AJ01-FliC), whereas other AjTLRs, such as AjToll and AjTLR3, do not. Further functional analysis reveals that knockdown of AjTLR2 results in a reduction in the typical weblike DNA structures of ETs, accompanied by a significant decrease in the expression of the ET-associated antimicrobial proteins H2A, H2B, and lysozyme. Furthermore, AjTLR2 knockdown similarly inhibits ET formation induced by recombinant AJ01-FliC protein. Mechanistically, the Apostichopus japonicus proto-oncogene tyrosine-protein kinase Src homolog (AjSRC), previously identified in our laboratory, is a downstream signaling molecule of AjTLR2 and is recruited via the TIR domain of AjTLR2. Knockdown of AjSRC also suppresses AJ01-FliC-induced ET formation. Collectively, our results indicate that the recruitment of AjSRC by AjTLR2 represents a potential regulatory pathway for AJ01-FliC induced ET generation.
Type I interferons (IFNs) are a class of pleiotropic cytokines that play a pivotal role in host defense against pathogenic invaders by binding with specific heterodimeric receptors. Among teleosts, these receptors consist of diverse subunits, including CRFB1, CRFB2, and CRFB5, whereas their pairing patterns and structural basis of interactions remain ill-defined. In this study, we identified and characterized three type I IFN receptor genes (CaCRFB1, CaCRFB2, and CaCRFB5) in the humpback grouper (Cromileptes altivelis), all sharing a common architecture of two extracellular FNIII domains. Furthermore, all three CaCRFB genes exhibited not only constitutive expression across all examined tissues but also significant transcriptional upregulation in response to poly I:C, LPS and pathogenic challenges (Vibrio harveyi and nervous necrosis virus), highlighting their active involvement in innate immunity. To elucidate their assembly mechanisms, we integrated molecular docking with co-immunoprecipitation (Co-IP) assays targeting their extracellular domains. Our results validated the canonical heterodimerization of the short-chain CaCRFB5 with both long-chain subunits (CaCRFB1 and CaCRFB2) as well as a noncanonical interaction of CaCRFB1/CaCRFB2, suggesting a more intricate receptor pairing in teleosts. Structural interface analysis revealed that these interactions are principally driven by electrostatic forces, including hydrogen bonds and salt bridges. Intriguingly, while the membrane-proximal FNIII domain II mediates canonical interactions (CaCRFB1/CaCRFB5 and CaCRFB2/CaCRFB5), it is the membrane-distal FNIII domain I that orchestrates the noncanonical CaCRFB1/CaCRFB2 pairing. These findings shed light on the structural basis of receptor heterodimerization, enriching the understanding of the teleost type I IFN system.
Han Zhang, Ting Wu, Ying Chen et al.· Developmental and Comparativ...· 0 citations
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