You need a mol wt of ~1.5 kDa before something is immunogenic. To raise
antibodies against smaller molecules they must be attached to a carrier
molecule, usually a protein. They are then HAPTENS and immunogenic.
Antibodies can then be raised to the hapten and the carrier.
Glycolipids and nucleic acids are also immunogenic together with large
xenobiotic compounds.
Simon Worrall
Lecturer in Biochemistry
University of Queensland
Australia