A protein comprising an antigen binding site of an antibody, wherein: (i) the protein binds to human granulocyte-colony stimulating factor receptor (hG-CSFR) and neutralizes granulocyte colony stimulating factor (G-CSF) signaling; and (ii) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the histidine at position 237 of SEQ ID NO:1 at a level at least 20 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (iii) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the methionine at position 198 of SEQ ID NO:1 at a level at least 20 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (iv) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the tyrosine at position 172 of SEQ ID NO:1 at a level at least 20 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (v) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the leucine at position 171 of SEQ ID NO:1 at a level at least 100 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (vi) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the leucine at position 111 of SEQ ID NO:1 at a level at least 20 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and; (vii) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the histidine at position 168 of SEQ ID NO:1 at a level no more than 5 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (viii) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the lysine at position 167 of SEQ ID NO:1 at a level no more than 5 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (ix) the antigen binding site does not detectably bind to the polypeptide of SEQ ID NO:1 in which an alanine is substituted for the arginine at position 287 of SEQ ID NO: 1; and (x) the protein binds to a conformational epitope in the hG-CSFR; and (xi) the protein inhibits G-CSF-induced proliferation of a BaF3 cell expressing hG-CSFR with an IC 50 of at least 1nM, wherein the IC 50 is determined by culturing 2x10 4 BaF3 cells in the presence of 0.5 ng/ml of hG-CSF for 48 hours, and wherein the proliferation of the BaF3 cells is determined by measuring 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction. (i) the protein binds to human granulocyte-colony stimulating factor receptor (hG-CSFR) and neutralizes granulocyte colony stimulating factor (G-CSF) signaling; and (ii) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the histidine at position 237 of SEQ ID NO:1 at a level at least 20 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (iii) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the methionine at position 198 of SEQ ID NO:1 at a level at least 20 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (iv) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the tyrosine at position 172 of SEQ ID NO:1 at a level at least 20 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (v) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the leucine at position 171 of SEQ ID NO:1 at a level at least 100 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (vi) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the leucine at position 111 of SEQ ID NO:1 at a level at least 20 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and; (vii) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the histidine at position 168 of SEQ ID NO:1 at a level no more than 5 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (viii) the protein binds to a polypeptide of SEQ ID NO: 1 in which an alanine is substituted for the lysine at position 167 of SEQ ID NO:1 at a level no more than 5 fold lower than it binds to a polypeptide of SEQ ID NO: 1; and (ix) the antigen binding site does not detectably bind to the polypeptide of SEQ ID NO:1 in which an alanine is substituted for the arginine at position 287 of SEQ ID NO: 1; and (x) the protein binds to a conformational epitope in the hG-CSFR; and (xi) the protein inhibits G-CSF-induced proliferation of a BaF3 cell expressing hG-CSFR with an IC 50 of at least 1nM, wherein the IC 50 is determined by culturing 2x10 4 BaF3 cells in the presence of 0.5 ng/ml of hG-CSF for 48 hours, and wherein the proliferation of the BaF3 cells is determined by measuring 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction.