Cytokines are regulatory proteins that are released by cells of the immune system. They are the means by which cells communicate in the generation of an immune response. Well-known cytokines include prostaglandin, the interleukins, the interferons and the lymphokines.
Cytokines trigger responses by binding to cell-specific receptors located in the cell membrane. This allows a distinct signal cascade to start in the cell, eventually generating biochemical and phenotypical changes in the target cell.
Production of a specific cytokine can be detected using the aforementioned ELISPOT assays, which can also determine the percentage of cells that produce the cytokine in question.