Polyclonal antibodies and antisera are the detection reagents of peptide research: raised in a host animal against a defined peptide immunogen, they recognise the target in tissue sections, on blots and in immunoassays. The antibodies section of the catalog is dominated by polyclonals rather than monoclonals for a specific reason — short peptides carry few epitopes, and a polyclonal response covering several of them detects the target more robustly than a single monoclonal clone against a molecule that may only be ten residues long.
Antiserum, purified IgG or affinity-purified: what you are actually buying
| Format | What it contains | Best for | Trade-off |
|---|---|---|---|
| Whole antiserum | Unfractionated serum: specific IgG plus all other serum immunoglobulins and proteins | RIA, EIA, applications tolerant of background; most economical per assay | High background on tissue and blots; total protein varies by bleed |
| Protein A/G purified IgG | Total IgG fraction, including non-specific antibodies | Applications needing a defined IgG concentration; conjugation | Specific antibody may still be a small fraction of total IgG |
| Affinity-purified (peptide column) | Only IgG that binds the immunogen peptide | Immunohistochemistry, immunofluorescence, low-abundance Western | Lowest yield and highest cost; still polyclonal in epitope coverage |
The glossary entries for antiserum, purified IgG and polyclonal versus monoclonal set out the distinctions in more detail. Catalog entries state which format each item is; "antibody" alone is not a sufficient specification.
The immunogen is the specification
Everything about a peptide antibody's behaviour follows from what it was raised against. The immunogen sequence tells you which region of the parent molecule is recognised, which determines three things you need to know before ordering. Does it distinguish processed forms? An antibody raised against the C-terminus of a peptide will not recognise a C-terminally extended precursor — which is exactly what you want if you are measuring the mature hormone, and exactly wrong if you are measuring total. Does it cross-react within the family? Antisera against the conserved mid-region of proglucagon products recognise glucagon, glicentin and oxyntomodulin alike. Is a modification required? Phospho-specific and amidation-specific antibodies are raised against modified immunogens and should not recognise the unmodified sequence — that specificity is the reagent's entire value in tau and neuropeptide work.
Host species, species reactivity and the two ways they matter
These are different specifications and both matter. The host species — usually rabbit, sometimes goat, sheep or guinea pig — determines which secondary antibody you need and which primaries can be multiplexed together. Two rabbit primaries cannot be distinguished by secondary in the same section. The species reactivity is which organisms' version of the target the antibody recognises, and it follows from sequence conservation, not from the host. A rabbit antibody raised against human amyloid-beta may or may not recognise the rodent sequence; the catalog entry states tested reactivity, and untested species should be treated as unknown rather than assumed. See species reactivity.
Validation: the controls that make a result publishable
Antibody specificity is the most common reproducibility problem in peptide research, and the controls are well established. The blocking peptide control is the primary one: pre-incubate the antibody with excess immunogen peptide, and specific staining or banding should disappear while non-specific signal persists. Most catalog antisera have a matching blocking peptide available, and using it is the difference between a suggestive image and an evidenced one. Beyond that: a knockout or knockdown sample where one exists, a secondary-only control, and — for quantitative claims — orthogonal confirmation by mass spectrometry or an independent antibody against a different epitope. Fields where antibody validation has been publicly disputed, such as irisin, are exactly where these controls are non-negotiable.
Application specifications and what they mean
Catalog entries list validated applications with suggested working dilutions — typically immunohistochemistry, immunofluorescence, Western blot, ELISA, RIA and immunoprecipitation. Two cautions apply. First, an antibody validated for one application may fail in another: reagents recognising conformational epitopes often work in immunohistochemistry and fail on a denaturing Western, while linear-epitope antibodies often show the opposite pattern. Second, working dilutions are starting points to be titrated in your own system, not fixed values — sample type, fixation and detection chemistry all shift the optimum. Immunoprecipitation work generally pairs the antibody with magnetic beads, and labeled antibodies carry the conjugates used for direct detection.
Storage and handling
Antibodies are proteins in solution and are handled quite differently from lyophilised peptides. Aliquot on arrival — this matters more for antibodies than for almost anything else in the catalog, because repeated freeze–thaw aggregates IgG and irreversibly reduces titre. Store single-use aliquots at −20 °C, or at 2–8 °C for a working aliquot in short-term use, and keep the preservative stated on the vial in mind: sodium azide is common and is incompatible with horseradish-peroxidase detection, so azide-containing antibodies must be dialysed before HRP conjugation. Lyophilised antisera should be reconstituted in the stated volume of water and then aliquoted immediately. Avoid frost-free freezers, whose defrost cycles subject stock to repeated partial thawing. The general principles are in the aliquoting guide and the storage guide.
Where antibodies fit against the other product types
Order an antibody when you need to detect or localise the endogenous molecule in tissue, cells or a lysate. Order the matching peptide standard as the blocking-peptide control and as a positive control on a blot. Order an ELISA or RIA kit when the question is how much target is present in a sample — the kit bundles a matched antibody pair, standards and a validated range, and is faster and more reproducible than assembling the parts. Start from the catalog hub, or from a topic such as Alzheimer's, cancer or diabetes, where antibody selection carries most of the experimental weight. All catalog items are supplied for in-vitro and approved animal research only, and none is a diagnostic reagent.