Induction of toll-like receptor (TLR) 2, and MyD88-dependent TLR- signaling in response to ligand stimulation and bacterial infections in the Indian major carp, mrigal (Cirrhinus mrigala)

Abstract

Toll-like receptor 2 (TLR2) is a member of TLR family. It recognizes a wide range of bacteria and their products, and is involved in inducing innate immune responses. In this article, we reported inductive expression of TLR2 and myeloid differentiation primary response gene 88 (MyD88)-dependent signaling in the Indian major carp, mrigal (Cirrhinus mrigala) which is highly commercially important fish species in the Indian subcontinent. Ontogeny analysis of TLR2, MyD88 and TRAF6 (TNF receptor associated factor 6) genes by quantitative real-time PCR (qRT-PCR) revealed constitutive expression of these genes in all embryonic developmental stages, indicating their involvement in embryonic innate immune defense system in fish. Tissue specific expression analysis of these genes by qRT-PCR showed their wide distribution in various organs and tissues. Highest expression of TLR2 was in gill, MyD88 in liver and TRAF6 was in kidney. Inductive expression of TLR2, MyD88 and TRAF6 genes were observed following peptidoglycan (PGN)-treatment, and Streptococcus uberis and Aeromonas hydrophila infections. Expression of interleukin (IL)-8 and TNF-α in various organs were significantly enhanced by PGN-treatment and bacterial infections, and were closely associated with TLR2 induction. These findings together highlighted the contribution of TLR2 in augmenting innate immunity in fish, and indicated it's important role in immune surveillance of various organs during pathogenic invasion. This study will enrich the information in understanding the innate immune mechanism in fish, and will be helpful in developing preventive measures against infectious diseases in fish.

Molecular cloning, characterisation and expression analysis of melanoma differentiation associated gene 5 (MDA5) of green chromide, Etroplus suratensis

“…Interestingly, in the present study, muscle showed the maximum MDA5 transcript level as compared to other tissues. Similar findings have been reported for genes associated with TLR signalling pathways such as tumour necrosis factor receptor-associated factor 6 (TRAF6) in mrigal, Cirrhinus mrigala (Basu et al, 2012). However, the exact functional role of the high expression is not known.…”

“…Similar to many immune-related genes, EsMDA5 also showed constitutive expression in all the tissues tested (Su et al, 2010;Ohtani et al, 2011;Basu et al, 2012;Rajendran et al, 2012). The mRNA expression was found to be highest in muscle followed by the spleen, head kidney and hindgut.…”

Early steps in the European eel (Anguilla anguilla)–Vibrio vulnificus interaction in the gills: Role of the RtxA13 toxin

“…In contrast, no il-8 mRNA regulation was observed after A. hydrophila in this model leading the authors to suggest a bacteria specific response [35]. Furthermore in the same study an upregulation of il-8 mRNA expression was observed in other tissues including liver, kidney, intestine and blood [35,36]. Our results are compatible with those found in carp although the expression level of this transcript in internal organs of the eels infected with V. vulnificus should be addressed in future analyses.…”

Repeated handling compromises the immune suppression and improves the disease resistance in overwintering channel catfish (Ictalurus punctatus)

“…The TLR2 is capable of recognizing a broad spectrum of microbes, partly due to its ability to form heterodimers with TLR1 and TLR6 [11]. It recognizes a wide range of bacteria and their products, and is involved in inducing innate immune responses [12]. Meanwhile, TLR3 play an important role in fish's defense against both viral and bacterial infection proved by the upper transcripts expression when challenged by poly:C and Vibrio parahemolyticus [13].…”