Cytokines are a class of signaling proteins that play a role in both the induction and effector phases of all immune and inflammatory responses, including cell proliferation, intercellular communication, and cell death. Cytokines are produced by a variety of hematopoietic and non-hematopoietic cell types and can exert autocrine and paracrine effects. They are related more correctly to hormones than to growth factors in their overall functions, but many cytokines also exhibit growth factor activity.
Growth factors are proteins that bind to receptors on the cell surface, with the primary result of activating cellular proliferation and/or differentiation. Growth factors are important for regulating a variety of cellular processes and are quite versatile, stimulating cellular division in numerous different cell types; while others are specific to a particular cell-type.