What kind of antigen(s) can be injected to get custom polyclonal antibodies?
Native proteins purified from the natural source, recombinant proteins fragments or full length proteins (expressed in a variety of hosts such as E. coli, Mammalian cells etc), chemical peptides (up to 22 aa) or other compounds of microbial, fungal or virus origin.

If the polyclonal antibodies are going to be used on the denatured target protein (example: Western blot, immunohistochemistry on fixed tissues), denatured forms of antigens are preferred (like gel piece, protein in inclusion bodies).
If the polyclonal antibodies are going to be used on native target proteins (example: immunoprecipitation), non-denatured forms of antigen are preferred (protein in solution free of denaturing agents).

Each of these categories has different strengths and weaknesses:
- Native proteins make excellent antigens and have traditionally been used to raise custom polyclonal antibody for different purposes. However, some proteins are not easy to isolate in sufficient amounts for characterization. Only a small fraction of these potentially useful proteins have been isolated and characterized. This renders most native proteins impractical as a means of generating custom polyclonal antibodies.

- The most logical alternative is recombinant protein which is usually produced in E. coli (see our standard Package 3 where recombinant protein production is included).
In consideration to their structure and size, proteins represent strong immunogens.
When using a whole protein as an antigen for your custom antibodies production, it is important to consider that there will be different binding sites meaning different epitopes detected which can decrease specificity but increase accessibility. As a consequence, the risk of failure, due to an inaccessible epitope for example, will be very low.
Fragments of proteins are generally easier to produce than a full length protein.

It overcomes the limitations of short peptides, but requires more effort and cost to produce them. ProteoGenix’ extensive experience in recombinant protein production ensures the highest success rate in the production of high quality antigen critical for the quality of your custom antibodies production.

- Chemical peptide is a popular antigen for polyclonal ab development.
Peptide synthesis is faster and cheaper than protein production but not all anti peptide antibodies will be able to recognize the native protein, therefore a careful choice of peptide sequence is of crucial importance, which is the reason why we always include peptide design using our own proprietary peptide design tool in our anti-peptide polyclonal antibodies services.

Anti-peptide antibodies show enhanced specificity which allows to:
- Eliminates or minimizes potential cross-reactivity between structurally homologous proteins.
- Enables the production of polyclonal antibodies to the targeted epitope.
- Enables the production of polyclonal antibodies for proteins with post-translational modifications.
- Enables discrimination between two or more isoforms of a protein. (It is also possible to choose a peptide present on 2 proteins if the purpose is to detect them both!)

Peptides are also very useful for antiserum production against post-translational modifications. See our phospho specific antibodies Package)

The antibodies generated against peptides usually work better for WB and ICH where antigens are completely or at least partly denatured.

The main risk with anti-peptide antibodies is that the antibody does not recognize the native protein if the polyclonal antibody binds an inaccessible epitope for example. It may also fail to give good polyclonal antibodies especially for immunoassays that display folded protein.
However, our peptide design tool can help solve such issues by predicting surface epitopes and post translational modifications.
We also usually recommend using 2 or 3 peptides to reduce the risk related to the accessibility of one epitope for antiserum production.