Cytokines are chemical messengers produced by virtually all the cells in our bodies, and effect changes in cellular behavior that are important in a number of physiological processes, including reproduction, growth and development, and injury repair. While many different cytokines have been identified, their individual functions are only partly known. In some cases, one cytokine can interact with a variety of different cell types and elicit different responses from each cell. In other cases, different cytokines can bring about the same response from one cell. The classification of cytokines is.