Identification of a beta 2 (CD18) molecule in a teleost species, Ictalurus punctatus Rafinesque

Beta 2, in combination with the alpha subunit, is responsible for tight adhesion of leukocytes, especially neutrophils and macrophages, in areas of inflammation. Although identified in mammalian and avian species; the beta 2 or CD18 molecule has yet to be identified in fish. The present investigation has identified a full-length channel catfish, Ictalurus punctatus, cDNA beta 2 molecule composed of 2.8 kb and a deduced amino acid sequence of 772 amino acids. The catfish molecule has an amino acid homology ranging from 54 to 63% with mouse, bovine, rabbit, human and chicken. The channel catfish molecule retains several characteristics of mammalian beta 2 molecules, such as cysteine-rich repeat regions, N-linked glycosylation sites, and several proposed signal sequences. Expression of the beta 2 molecule on the catfish neutrophil cytoplasmic membranes is increased upon phorbol dibutyrate stimulation of the cells. Based on Western blotting and the immunoprecipitation test, the channel catfish beta 2 molecule has a molecular mass of approximately 95 kD, essentially the same as that for mammalian species. However, two additional molecules, perhaps α chains, of unexpected molecular mass appear to co-precipitate in the SPIT with the 95 kD CD18 molecule. These results confirm the existence and expression of a beta 2 gene in channel catfish, a species phylogenetically distant from mammalian species.