Expression of Toll-like receptor 21 (TLR21) in koi carp (Cyprinus carpio) infested with anchor worm, Lernaea sp.

Toll-like receptors (TLRs) are transmembrane receptors that recognize different types of pathogen associated molecular patterns (PAMPs) and play a key role in activation of immune system. Among the TLRs reported so far, TLR21 is unique to fishes and its ligand has not been identified. Parasite infestation of fishes with Lernaea sp. results in economic loss in aquaculture operations, as disfigurement of food and ornamental fishes by these parasites render them unsuitable for sale. The objective of this study was to compare the expression of TLR21 in healthy and Lernaea sp. infested koi carp (Cyprinus carpio). Comparison of TLR21 expression by reverse transcriptase polymerase chain reaction (RT-PCR) showed detectable expression of TLR21 in parasite infested fishes and no detectable expression in healthy fishes. This is the first study on the expression of TLR21 in parasite infested fish.