Ans.
Cytokines are small chemical molecules, secreted by immune cells and play important role in cell signaling processes. Cytokine that increases growth and development of myeloid stem cells is GM-CSF (granulocyte-macrophage colony stimulating factor).
The myeloid progeniter cell is precursor for monocytes, granulocytes, platelets, and erethrocytes. The monocytes get developed into macrophages that help in digestion of pathogens. Thus, GM-CSF is released by various immune cells to increase the formation of macrophages as an immune response. Hence, the correct answer is 'GM-CSF.'