Cytokines and Growth Factors

Cytokines are a broad and loose category of small proteins important in cell signaling. Cytokines typically exert their functions by interacting with specific cytokine receptors on the target cell surface. Growth factors are secreted biologically active molecules that can affect the growth of cells. This definition has become expanded to include secreted molecules that promote or inhibit mitosis or affect cellular differentiation. Growth factors can act on specific cell surface receptors that subsequently transmit their growth signals to other intracellular components and eventually result in altered gene expression. Some growth factors are small peptides called cytokines. While all cytokines affect signal transduction pathways, only those cytokines affecting cell growth/differentiation signaling pathways are considered growth factors.