Glossary
Immunogen
An immunogen is the material used to immunise a host and raise an antibody. Why short peptides need a KLH or BSA carrier; the sequence predicts specificity.
An immunogen is whatever material is used to trigger an immune response in order to generate an antibody. It is not synonymous with antigen: all immunogens are antigens, but plenty of antigens — including short peptides — are too small to set off a response unaided. Molecules like these are called haptens, and they require assistance.
Carrier proteins and the most important datasheet field
Peptides smaller than about 5 kDa are coupled to a carrier protein. KLH (keyhole limpet haemocyanin) is favoured for immunisation, being large, strongly immunogenic and evolutionarily remote from mammals, whereas BSA or ovalbumin goes on the screening plate so that antibodies against the carrier are not confused with antibodies against the peptide. The coupling chemistry is also relevant — glutaraldehyde, EDC, or maleimide through an extra terminal cysteine — since the attached end is mostly concealed from the immune system, skewing antibodies toward the free terminus.
In practice, the immunogen sequence is the field on an antibody datasheet with the greatest predictive value. It shows which epitope is probably bound, which analogues are likely to cross-react, and whether the sequence is conserved in the species you work with. The corresponding free peptide is supplied as a blocking peptide.
Related terms and material
antiserum · ELISA. Reference material: antibodies, peptide libraries.