Immunochemistry: a branch of chemistry that involves the study of the molecular mechanisms underlying the function of the immune system, especially the nature of antibodies, antigens and their interactions. Various methods in immunochemistry have been developed and refined, and been used in scientific study, from virology to molecular evolution. Immunochemistry is also studied from the aspect of using antibodies to label epitopes of interest in cells (immunocytochemistry) or tissues (immunohistochemistry)