Purity ~95% (SDS-PAGE). Granulocyte colony stimulating factor (GCSF) is a pleiotropic cytokine best known for its specific effects on the proliferation, differentiation, and activation of hematopoietic cells of the neutrophilic and granulocyte lineage (1). GCSF plays an important role in defense against infection, in inflammation and repair, and in the maintenance of steady state hematopoiesis. Cell activation by GCSF is mediated by granulocyte colony stimulating factor receptor alpha (GCSF R? also CD114), a 95 105kD type I transmembrane protein and member of the cytokine receptor superfamily, type I cytokine receptor family, and type 2 subfamily of receptor proteins. Mouse GCSF R is synthesized as an 837 amino acid (aa) precursor that contains a 25 aa signal sequence, a 601 aa extracellular domain (ECD), a 24 aa transmembrane region, and a 187 aa cytoplasmic tail. The ECD contains one Ig like C2type domain, five fibronectin typeIII domains, and 11 potential sites for N-linked glycosyl