Interleukin-1β(IL-1β)is a key mediator of inflammation and orchestrates a variety of immune responses by initiating gene expression.IL-1β was not identified from nonmammalian species until recently.However,no IL-1β genes have been reported from Siluriformes fishes class in China.In this study,we have cloned and sequenced the IL-1β in Mystus macropterus by RT-PCR and RACE-PCR methods.It contains 1 194 nucleotides,including 3′UTR of 224 nucleotides,5′UTR of 82 nucleotides,and an open reading frame with 888 nucleotides encoding a 296 amino acid peptide with MW of 33.84 ku and PI of 5.00.Compared with eight vertebrates species,IL-1β in M.macropterus shared the highest identity(79.0%)with that in Ictalurus punctatus,and the lowest identity(22.0%)with that in Gallus gallus.Phylogenetic tree analysis based on some IL-1β amino acids indicated that IL-1β amino acids in M.macropterus were clustered closely with Ictalurus punctatus.Expression analysis indicated that the IL-1β gene of M.macropterus was detected in muscle,brain,spleen,head kidney,kidney,stomach,skin,liver and intestine in varying degrees,and increased significantly in head kidney and spleen on 1 day after injection with Aeromonas hydrophila and returned to the normal level 15 d later.The result indicated that M.macropterus IL-1β plays a critical role in the host-pathogen interaction.