One of the most commonly asked questions is: how much of the antigen-specific antibody (against a given protein or other antigen) is there in serum?
The answer is that it varies between antibody productions, and that in serum, the specific antibody amount is not determined. When serum is subjected to affinity purification on Protein A or G, it yields a total immunoglobulin fraction, with the specific antibody constituting 0.5-5 % of the total antibody pool. Concentration of total IgG in rabbit serum vary from 10-20 mg/ml.
Most antigen-specific antibodies are purified in a process called antigen affinity purification, where serum is passed through a column of beads coupled to the antigen (protein or peptide). Such an antibody format is most suitable for immunolocalization, immunoprecipitation and ChIP. The amount of specific antibody/tube will be the highest in antigen-purified serum antibody format.