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The term polyclonal antibodies (pabs as opposed to mabs) can cause some confusion. There are pabs raised to full length protein, pabs to large fragments of protein and pabs to small peptides. In addition there are differences between antiserum, proteinA/G purified and antigen affinity purified pabs.
The general concept of pabs is that they are a collection of antibodies against multiple epitopes and possibly against multiple proteins. When an antibody is raised to an entire protein, it is easy to see how multiple parts of the protein will generate a collection of different specificities and affinities. This is beneficial for certain applications such as IP and WB. Also for IHC this can be useful as long as there is no cross-reaction with any other proteins. This can be addressed by comparing endogenous vs knock-down, un-induced cells (without expression) vs induced cells (with expression) or looking at tissues where the expected protein is at one particular compartment.
Antibodies to a protein fragment will likely show higher specificity when the fragment is unique for the protein of interest. Then the advantages of the pabs are combined with the uniqueness of the antigen.
Although such antibodies cannot compete with the mono-specific characteristics of mabs, they can work together in sandwich type ELISA or for IP.
When instead of a protein or protein fragment a small peptide is used as the antigen, then the characteristics of mabs are approached. It would be a prerequisite to have the peptide antibodies affinity purified, but this gives such pabs the upper hand over mabs with low affinity. The cost of generating peptide antibodies are also competing as neither expensive screening and sub-cloning, nor protein purification steps of the antigen is required. A ten to 15 aa peptide is easy and quickly synthesised and delivered by a specialist service. Only linking the peptide to a carrier protein and dialysis is required to have the material ready for immunization. And the peptide will subsequently be used for the affinity purification.
Peptide antibodies therefore are versatile tools combining the mono-specificity of the mabs with the high affinity of polyclonal antibody while being low in the production costs.
Antiserum and protein A or protein G purified IgG will still have a mixture of affinities and specificities. Only antigen-affinity purified antibodies will have the highest grade and particularly so when they are peptide-derived. For those who struggle to find a fit-for-purpose antibody we offer our custom antibody services.