Cytokines are small proteins that are produced by cells in the immune system. They play a crucial role in cell signaling and communication, particularly in regulating the immune response. Cytokines can be produced by various cells, including immune cells, and they act as chemical messengers to stimulate or inhibit the activity of other cells. They are involved in a wide range of biological processes, such as inflammation, cell growth and differentiation, and immune system regulation. Cytokines can have both pro-inflammatory and anti-inflammatory effects, depending on the specific cytokine and the context in which it is produced.