Antiserum

Antiserum is the entire serum harvested from an animal following immunisation: the blood is left to clot, cells and fibrin are taken out, and the remaining liquid is the product. Importantly, it holds not only the antibodies generated against your immunogen but also the full immunoglobulin repertoire the animal already had, together with albumin, complement factors and serum proteases.

Why the format is important

In a typical antiserum, antibody specific to the target makes up just a few percent of total IgG. Where surplus unrelated protein does no harm — many ELISA and dot-blot applications, or immunohistochemistry at high dilution — antiserum is the least expensive and most avid choice, and its high overall protein content even serves as a built-in carrier. For work that involves conjugation, needs low background or depends on a known protein concentration, that surplus becomes a drawback: labelling reactions modify every IgG molecule without discrimination, and non-specific serum binding pushes background up.

An antiserum’s titre is given as the working dilution that yields an acceptable signal rather than as mg/mL of specific antibody, since the specific concentration is usually not known. A preservative — sodium azide or glycerol — is normally included, which is incompatible with HRP conjugates and should be verified before starting.

Related terms and material

purified IgG · polyclonal vs monoclonal · species reactivity. Reference material: antibodies catalog. Further reading: antiserum vs purified IgG.