Molecular characterization and expression analysis of interleukin-1 beta in Japanese eel (Anguilla japonica)

Interleukin 1-beta (IL-1B) is a key proinflammatory cytokine involved in disease resistance. In recent years, il-1β genes from several teleosts have been cloned. The Japanese eel (Anguilla japonica) is an evolutionarily primitive fish widely farmed in East Asia. The il-1β gene has not yet been cloned from Japanese eel. In this study, the complete cDNA of il-1β was successfully sequenced from peripheral leukocytes through the rapid amplification of cDNA ends. The il-1β gene consists of five exons and four introns, and the full-length cDNA spans 1204 bp, comprising a 99-bp 5' untranslated region, a 750-bp coding sequence, and a 355-bp 3' untranslated region. The deduced amino acid sequence includes a consensus IL-1 family signature but lacks both a signal peptide and an IL-1 converting enzyme cleavage site, similar to other teleost IL-1B proteins. Homology analysis revealed that Japanese eel IL-1B is highly conserved within the order Anguilliformes, sharing the highest similarity with American eel (Anguilla rostrata), followed by conger eel (Conger myriaster). Tissue expression analysis showed that il-1β is constitutively expressed in multiple tissues, with high expression in peripheral leukocytes and the spleen; moderate expression in the gill, liver, head kidney, trunk kidney, and intestine; and low expression in the heart, stomach, skin, and muscle. In vitro stimulation with zymosan, polyinosinic-polycytidylic acid, and lipopolysaccharide upregulated il-1β expression in peripheral leukocytes.