Toll-like receptor 2 (TLR2) functions as a key regulator of inflammatory responses to Vibrio parahaemolyticus infection in the Manila clam (Ruditapes philippinarum).
Jul 2026· Fish and Shellfish Immunology· Vol 177, pp.
111587
· 0 citations· 48 references
Medicine
TL;DR
Findings indicate that RpTLR2 acts as a positive regulator of V. parahaemolyticus-induced inflammatory responses and improve understanding of TLR2-mediated innate immunity in mollusks and provide a molecular basis for studying host-pathogen interactions in bivalves.
Abstract
Toll-like receptor 2 (TLR2) is a pivotal pattern-recognition receptor in innate immunity. It is well characterized in vertebrates but remains poorly understood in mollusks. In this study, we identified a TLR2 homolog (RpTLR2) in Ruditapes philippinarum encoding a 575-amino acid protein with a canonical Toll/interleukin-1 receptor (TIR) domain. Phylogenetic analysis placed RpTLR2 within the molluscan TLR2 clade, confirming its evolutionary conservation. RpTLR2 was constitutively expressed in all examined tissues, with the highest transcript levels in the gill and mantle. After Vibrio parahaemolyticus challenge, RpTLR2 mRNA and protein levels were significantly upregulated. Functional assays showed that RpTLR2 overexpression intensified inflammatory responses and increased the expression of key inflammation-related genes, whereas RNA interference-mediated RpTLR2 knockdown markedly reduced V. parahaemolyticus-induced inflammation in gill cells. Overall, our findings indicate that RpTLR2 acts as a positive regulator of V. parahaemolyticus-induced inflammatory responses. These results improve understanding of TLR2-mediated innate immunity in mollusks and provide a molecular basis for studying host-pathogen interactions in bivalves.
The RelA subunit is a core component of the nuclear factor-kappa B (NF-κB) family and plays a pivotal role in regulating immune and inflammatory responses across vertebrates and invertebrates. However, its functional role remains poorly defined in marine bivalves. In this study, a RelA homolog (RpRelA) was identified and functionally characterized in the Manila clam (Ruditapes philippinarum). The full-length cDNA of RpRelA is 2055 bp, encoding a 684-amino acid protein containing a conserved Rel homology domain (RHD) and an IPT domains. Both its tertiary structure and amino acid sequence are highly conserved across species. Phylogenetic analysis indicated that RpRelA clusters with invertebrate Rel family members. Quantitative real-time PCR (qRT-PCR) revealed that RpRelA is ubiquitously expressed in all examined tissues, with the highest expression levels detected in haemocytes and gills. Following V. parahaemolyticus challenge, both the mRNA and protein levels of RpRelA were significantly upregulated. Consistently, nuclear-cytoplasmic fractionation Western blot and immunofluorescence analyses confirmed its robust nuclear translocation upon bacterial infection. Furthermore, overexpression of RpRelA significantly upregulated pro-inflammatory genes (RpIL-17 and RpTNF) and caused severe gill inflammation, whereas its silencing suppressed their expression and alleviated the inflammatory response. Collectively, these results demonstrate that RpRelA, as a core NF-κB subunit, positively regulates the inflammatory response during V. parahaemolyticus infection in Manila clam, and provide new insights into the immune regulatory mechanism of bivalves against bacterial infection.
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