Immunochemistry involves working with components of the immune system. These materials may include antibodies, signaling molecules such as cytokines, and cells that function in the immune system. Antibodies are proteins that are made by the immune system. They bind to specific molecules and are frequently used in tests to detect those molecules. One type of test that uses antibodies is called an ELISA (Enzyme Linked ImmunoAssay).
ELISAs are frequently used in medical diagnostics but may be used in area where it's important to detect some kind of molecule in a specific way.