Answer:
antibodies
Explanation:
Antibodies are soluble mediators of the immune system.
They are also known as immunoglobulins and are bifunctional molecules.
They consist of polypeptide chains with an antigen binding site and a site that carries out the biological activity of the molecule.
Antibodies are expressed on the cell surface of B cells. When these B cells are stimulated by antigen, they differentiate into antibody-secreting plasma cells. The antibodies secreted then serve as effector molecules for cells functioning in the innate and/or adaptive immune systems.
For example, particular antibodies trigger the activation of the classic complement pathway.
