Custom antibody: when to order one, and what to specify

Deciding and specifying

1. Rule the catalogue out properly first. Before commissioning, establish whether existing reagents genuinely fail or were used outside their validated application. A catalogue antibody validated for one application and used in another is the most common false negative, and finding that out costs a great deal less than a custom project.
2. Write the application into the specification. State the assay, the sample type, the fixation and the species. An antibody that must work on fixed tissue, on a denatured blot and in a live-cell assay is three different reagents, and a provider that agrees to all three without comment is not reading the request.
3. Choose the epitope deliberately. Where you raise against determines what you can distinguish: an isoform, a modification state, a species orthologue or a domain. Say what must be discriminated and what must be recognised across, and require a counter-screen that tests it.
4. Plan validation before the project starts. Decide what evidence will convince you the antibody works, including a genuine negative control such as a knockout or knockdown sample. Projects without a defined acceptance test end in an argument about whether a band is the right band.
5. Secure renewability. Ask for the sequence or the clone. A custom polyclonal is a finite reagent, and a programme that will run for years should pay the extra for something that can be made again.

Where projects for custom antibodies actually fail

The common failures are an immunogen that does not represent the folded protein, a screen that does not resemble the application, and the absence of a real negative control during validation. All three are decided before any animal is immunised, which is why the specification conversation is the project.

A less common but expensive failure is a target so conserved that the host does not raise a response. Providers can often predict this from the sequence, so ask before contracting.

What you should receive

The antibody in a stated format and buffer, the immunogen description, the screening data including the counter-screen, the validation data in the specified application, a lot certificate, and the clone or sequence where the contract provides for it.

Ask for a retained reference aliquot. It is the only way to test a future lot against the reagent you originally validated.

Reading an antibody catalog: coverage is not validation

A long list of products against a target says the target is popular, not that a reagent works. Read for the evidence type instead: a genetic control, an independent user's data, validation in the application you need. A target with twenty products and no knockout figure anywhere is a target nobody has validated.

Read the immunogen rather than the description. The sequence or region tells you which isoforms the antibody can possibly see, which species, whether a modification site falls inside it and whether a family member shares it. A supplier who will not disclose it is asking you to take the specificity claim on trust.

Lots, identifiers and the literature

Persistent reagent identifiers let you find every published use of the same product, including the uses that went badly, and that literature is more informative than any datasheet. It costs a few minutes and it is the step most often skipped.

For a polyclonal, ask the lot number, whether the data shown came from that lot, and how much remains. For a project running over months, securing a single lot removes a variable that cannot be controlled retrospectively, and recording the lot with every result is what makes the data auditable later.

What a trial vial or free antibody samples can and cannot answer

A small sample is enough to ask whether a reagent gives a plausible signal in your hands on your own material. That is a useful screening question and it is the whole of what a trial answers.

It is not enough to establish specificity, which needs a genetic control, and it is a poor basis for a project, because the lot may not be available again. Treat it as a screening step with a known limit rather than as a validation.

An rspo3 antibody and a secreted Wnt amplifier

R-spondin 3 is secreted and potentiates Wnt signalling through its own receptors, so an rspo3 antibody often reports conditioned medium as well as cells and the collection time belongs in the method. The family members are similar, so specificity data matter, and the pathway readout rather than the ligand's level is what supports a signalling claim.

An hdac5 antibody and a class II deacetylase

HDAC5 shuttles between nucleus and cytoplasm under phosphorylation control, so an hdac5 antibody is read as a location rather than a level and a fractionation with markers is the preparation. The class shares domains, so specificity against HDAC4 and HDAC7 is the line to read, and activity in this class depends on partner complexes rather than on the enzyme alone.

An shmt2 antibody and one carbon metabolism

SHMT2 is the mitochondrial enzyme of the folate one carbon cycle, so an shmt2 antibody is read with a mitochondrial marker and its cytosolic paralogue is the cross reactivity to exclude, since the two differ in localisation rather than in sequence alone. Flux belongs to a labelled tracer, and the antibody reports the expression difference between conditions.

A nup98 antibody and a nuclear pore component

NUP98 is a pore complex component and also the fusion partner in several leukaemia rearrangements, so a nup98 antibody has to say where its epitope lies: an antibody against the region retained in a fusion detects both, which is useful or confounding depending on the question. The pore gives a punctate rim pattern that is its own control.

Common questions

When should I order a custom antibody?

When no catalogue reagent exists for the target, when you need to distinguish an isoform, modification or species that existing reagents cannot, or when you have genuinely established that available reagents fail in your validated application.

How long does a custom antibody take?

It is set by the immunisation and screening schedule rather than the provider. Polyclonal projects are considerably shorter than monoclonal or recombinant ones, which add cloning, sequencing and expression.

What should the specification contain?

The target and the epitope region, what must be discriminated and what must be recognised across, the assay and sample type, the host and format, the screening format, and the acceptance criteria for validation.

How do I validate a custom antibody?

In the application it was commissioned for, with a real negative control such as a knockout, knockdown or non-expressing sample. A signal at the right size is not validation on its own.

How do I judge research antibodies before buying them?

Look for a genetic control, validation in your application and species, a disclosed immunogen and a persistent identifier you can search the literature with. The number of products against a target measures popularity, not evidence.

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