Hapten

Hapten, also known as incomplete antigen, refers to simple small molecule antigen that only has immune response specificity but no immunogenicity, such as certain polysaccharides, lipids, and drugs. The molecular weight of the hapten is too small to stimulate the immune response, and it must bind to the carrier to stimulate the immune response. Haptens have active groups that facilitate coupling with protein carriers, like -COOH, -NH2,-OH, -SH, etc.