Molecular, cellular, and functional characterization of chicken cytokines homologous to mammalian IL-15 and IL-2

DNA sequence analysis of a chicken interleukin (IL)-15 cDNA identified a 18 7 amino acid open reading frame encoding a protein with a predicted molecul ar weight of 21,964 Da, two potential N-linked glycosylation sites, four hi ghly conserved Cys residues, two out-of-frame AUG initiation codons in the 5' untranslated region, and an unusually long (66 amino acid) signal peptid e such that the expected size of the mature protein is 14,462 Da. Chicken I L-15 and IL-2 were compared with regard to their molecular,, cellular, and functional characteristics. The predicted amino acid sequences of both chic ken cytokines showed greater homologies with mammalian IL-15s compared with mammalian IL-2s. Nor-them hybridization and RT-PCR demonstrated chicken IL -15 gene transcripts in a wide variety of tissues and cell types while the chicken IL-2 gene was expressed only in concanavalin A (con A)-activated sp leen cells. Both recombinant cytokines stimulated the growth of spleen T-ce lls and enhanced the activity of natural killer (NK) cells in vitro. Subcut aneous injection with an expression plasmid encoding IL-15 increased the pe rcentage of CD3(+) spleen T-lymphocytes whereas injection of an IL-2 cDNA a ugmented CD3+, CD4(+), CD8(+), T-cell receptor (TCR)1(+), and TCR2(+) T-cel ls. Collectively, these results indicate that chicken IL-15 and IL-2 are T- cell growth factors potentially capable of enhancing cell-mediated immunity in vivo. Published by Elsevier Science B.V.