Clinical studies show that many cytokines play a crucial role in cancer, infectious diseases, allergy, inflammatory, autoimmune diseases and graft rejection.Measurements of cytokine levels are useful for understanding pathogenesis and as diagnostic and prognostic indicators.Cytokines may be pleiotropic (one cytokine, multiple effects), redundant (multiple cytokines, one effect) and antagonistic (one cytokine inhibits another cytokine). Cytokine actions may be grouped into five broad areas: