Peptide Antibodies and Antisera: Formats, Immunogens and Validation Controls

Antisera and polyclonal antibodies do the detection work in peptide research. An animal is immunised with a defined peptide immunogen, and the resulting antibodies then find that target in immunoassays, on membranes and in sections of tissue. Why does the catalogue's antibodies section contain so many more polyclonals than monoclonals? Because a molecule of around ten amino acids exposes only two or three epitopes, and antibodies distributed across several of them will detect it much more consistently than one clone directed at a single site.

Three formats behind the word "antibody"

For fuller definitions, see the glossary items covering antiserum, purified IgG and the polyclonal/monoclonal distinction. Every listing says which of the three you are getting, because on its own the word "antibody" tells you nothing about the product.

The immunogen is what really defines the reagent

A peptide antibody behaves exactly as its immunisation dictates. Knowing the immunogen sequence tells you which portion of the parent molecule the antibody will see, and three practical questions follow from that. Does it discriminate between processed forms? Raise an antibody against the C-terminal end and it will be blind to a precursor that extends past it — perfect if the mature hormone is your analyte, wrong if total content is. Does it stay within one molecule? Antisera made against the conserved mid-portion of proglucagon products bind glucagon, oxyntomodulin and glicentin without discrimination. Does it need a post-translational modification? Phospho-specific and amidation-specific antibodies come from correspondingly modified immunogens and ought to ignore the plain sequence entirely — in tau and neuropeptide work, that is the entire reason for using them.

Host species and species reactivity are not the same thing

These are two separate specifications and each matters for a different reason. The host — usually rabbit, occasionally sheep, goat or guinea pig — determines which secondary antibody you need and which primaries can be combined in a multiplex; two rabbit primaries on the same section cannot be distinguished by secondary. Species reactivity, in contrast, says whose version of the target the antibody binds, and that follows from how conserved the sequence is, not from the host animal. An antibody raised in rabbit against human amyloid-beta may or may not recognise the rodent sequence: the listing states what has been tested, and whatever has not been tested should be treated as unknown rather than assumed. See species reactivity.

The controls that let a result be published

Nothing contributes more to irreproducibility in this field than antibody specificity, and the remedies have been known for a long time. Foremost is the blocking peptide: pre-absorb the antibody with a surplus of its immunogen, and the authentic staining or band should be abolished while anything non-specific stays put. A matching blocking peptide is offered for most of the antisera we list, and running it is the difference between a picture that looks convincing and a result that is evidence. Then add a secondary-only lane, and a knockout or knockdown material if such a thing exists for your target. Quantitative statements need backing from an orthogonal source — either confirmation by mass spectrometry or a different antibody against a separate epitope. In areas where published validation has been contested, and irisin is the standard illustration, none of this is discretionary.

Reading the application specifications

Each listing names the applications in which the antibody has been validated and gives a starting dilution — commonly immunoprecipitation, immunofluorescence, immunohistochemistry, Western blot, ELISA and RIA. Two things to bear in mind. Being validated for one application says nothing about another: an antibody that reads a folded epitope may work superbly on fixed tissue yet give nothing after SDS denaturation, and an antibody against a linear epitope frequently shows the opposite pattern. And the dilution quoted is a starting point for titration under your own conditions rather than a specification, because detection chemistry, fixation protocol and sample type all move the optimum. Immunoprecipitation usually means pairing the antibody with magnetic beads, and conjugates for direct detection come from the labelled antibody range.

Storage and handling

An antibody arrives as protein already dissolved, which makes its handling quite unlike that of a lyophilised peptide. Divide it up the day it arrives: nothing else in the catalogue suffers as much from freeze-thaw, since each cycle aggregates a portion of the IgG and takes the titre down for good. Single-use portions go at −20 °C, while the aliquot in current use may be held at 2-8 °C. Read which preservative the vial contains: azide is widespread and it blocks peroxidase-based detection, so anything containing it needs dialysis before being conjugated to HRP. Freeze-dried antisera should be reconstituted with the stated volume of water and split without delay. Keep them out of frost-free freezers, where every defrost cycle thaws part of the contents. The general rules are in the storage and aliquoting guides.

How antibodies relate to the other product types

An antibody is the right purchase when you want to find or localise the endogenous molecule in a lysate, in cells or in tissue; buy the corresponding peptide standard alongside it, both as a pre-absorption control and as a positive control on the membrane. When the question is instead how much of the target is present, a RIA or ELISA kit is the better answer, because it arrives with standards, a validated working range and an antibody pair already matched — quicker and steadier than putting the same assay together yourself. Begin either at the catalogue hub or in a specific topic, such as diabetes, cancer or Alzheimer's, where the antibody choice does most of the work. Every product listed is intended for in-vitro experiments and approved animal studies, and none of them is a diagnostic device.