Neutrophils are one of the essential components of the innate immune system that play a critical role in the host's defense against bacterial and fungal infections. Hematopoietic growth factors are a class of regulatory cytokines that are required for stimulation, proliferation, and differentiation of blood cells. Granulocyte-colony stimulating factor (G-CSF) is a member of this regulatory family of cytokines that almost exclusively stimulates proliferation and differentiation of precursor neutrophilic cells in the bone marrow and modulates functional activities of mature neutrophils in the circulation. Treatment with G-CSF significantly enhances phagocytic, bactericidal, and fungicidal activities of neutrophils. A cDNA clone encoding bovine G-CSF (bG-CSF) was isolated and sequenced from an endothelial cell cDNA library. The full-length cDNA is 1460 nucleotides with 585 nucleotides comprising the open reading frame. The deduced G-CSF protein consists of 174 amino acids with a 21 amino acids-long signal peptide. This cDNA was expressed in Escherichia coli and the biological activities of the solubilized protein from purified inclusion bodies were examined. Flow cytometric analysis of membrane antigen density of neutrophils activated with this oxidized and refolded protein revealed an upregulation of CD11a, CD11b, CD11c, and CD18. Expression of CD62L was decreased while expression of CD14 remained unchanged. These findings indicate that recombinant bG-CSF expressed in E. coli is biologically active and exerts the same type of effects on neutrophils in vitro as those of human G-CSF (hG-CSF). Bovine G-CSF cDNA was also subcloned into a mammalian expression vector and tested for its in vivo efficacy as an immunomodulator in calves. Results obtained from the preliminary studies were inconclusive. Using the same endothelial cell cDNA library mentioned above, we also cloned and sequenced a full-length cDNA encoding bovine interleukin-7 and a partial cDNA sequence encoding bG-CSF receptor.