Cytokines are proteins regulating the development and duration of normal and pathological immune response. They are responsible for the transduction of informations among immune system cells and are involved in the communication between the immune and neuroendocrine systems. Cytokines play roles in the immune response, hematopoiesis, apoptosis, inflammation and homeostasis. Distinct lymphocyte populations are characterized by the spectrum of synthesized cytokines and their production may be altered in diseases.