Receptors are proteins, usually cell surface receptors, which bind to ligands and cause responses in the immune system, including cytokine receptors, growth factor receptor and Fc receptor. Receptors can be found in various immune cells like B cells, T cells, NK cells, Monocytes and stem cells. A molecule that binds to a receptor is called a ligand, and can be a peptide (short-protein) or another small molecule such as a neurotransmitter, hormone, pharmaceutical-drug, toxin, or parts of the outside of a virus or microbe. When a ligand binds to its corresponding receptor, it activates or inhibits the receptor's associated-biochemical pathway.
Receptors can induce cell growth, division and death; control membrane channels or regulate cell binding. Receptors play an important role in signal transduction, immunetherapy and immune responses.