Receptors are proteins, usually cell surface receptors, which bind to ligands and cause responses in the immune system. Receptors can be found in various immune cells like B cells, T cells, NK cells, monocyte 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.
Recombinant protein is a manipulated form of protein, which is generated in various ways to produce large quantities of proteins, modify gene sequences and manufacture useful commercial products. The formation of recombinant protein is carried out in specialized vehicles known as vectors. Recombinant technology is the process involved in the formation of recombinant protein.