Choosing reagents against the most polymorphic proteins in the genome: why an hla-dr antibody, an hla-a antibody, an hla-abc antibody, an hla-g antibody, the hla g antibody spelling beside it and an mhc class i antibody each have to state which allele groups they detect, what happens to a stain when a donor carries an allele the clone does not see, how a b2m antibody or a class I framework reagent gives a more even readout when total surface class I is the question, where a cd74 antibody and an ido antibody or ido1 antibody report the presentation machinery rather than the molecule, what an arg1 antibody or arginase 1 antibody and a macrophage antibody add about the suppressive environment around it, and why loss of presentation has to be shown with more than one reagent

Designing a presentation experiment

1. Establish what allele groups the clone covers. Datasheets vary in how clearly they state this, and it is the single most important property. A pan reagent against a conserved framework region is safer than an allele specific one when total surface expression is the question.
2. Use a partner chain as a cross check. The invariant light chain of class I is not polymorphic, so a reagent against it gives an allele independent measure of surface class I. Disagreement between it and a heavy chain reagent is informative.
3. Interpret loss with two independent reagents. Apparent downregulation with one clone can be an allele the clone does not see. Two reagents recognising different regions, agreeing, is the minimum for a loss claim.
4. Include an interferon treated positive control. Presentation molecules are strongly induced by interferon, which gives a reliable high expression control and shows the stain has dynamic range on your cells.
5. Separate surface from total. Total protein can be unchanged while surface presentation collapses, because the block is in loading or trafficking. Surface staining of live cells answers the question that a permeabilised stain does not.

Polymorphism is the technical problem

Everywhere else in immunostaining, a reagent either binds the target or does not. Here it binds some versions of the target and not others, and the versions are distributed across donors in a way that correlates with ancestry.

That makes reagent choice an equity issue as well as a technical one in human studies: a clone with uneven allele coverage produces systematically different results in different populations.

Surface is the biology

What matters for presentation is molecules on the surface with peptide loaded. Total protein measured in a lysate can be normal while the surface is empty because loading or trafficking is blocked.

Stain live cells without permeabilisation when surface expression is the claim, and say so in the methods. It is a different measurement from the permeabilised one and readers cannot tell which was done unless it is stated.

Common questions

Why do two donors stain so differently?

Frequently genotype rather than expression. Clones recognise epitopes present in some allele groups and absent in others, which is why a framework or partner chain reagent is safer for comparing donors.

How should loss of presentation be demonstrated?

With two independent reagents, a surface rather than total measurement, and an interferon treated positive control on the same cells. One clone showing reduced staining is not sufficient.

What is a good positive control?

Interferon treatment, which strongly induces presentation molecules on most cell types. It calibrates the upper end of the stain and confirms the reagent detects induction.

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