Anti human IgG antibody: choosing a secondary reagent by what it must not bind

Reading the specification of a human igg1 antibody

1. Match the chain, not just the species. A reagent against whole immunoglobulin binds both heavy and light chains and therefore cross reacts with other classes sharing light chains. A reagent against a specific heavy chain or a specific fragment is narrower and is what multiplexing requires.
2. Choose the host to avoid the sample. The secondary must be raised in a species unrelated to the sample and to any other reagent in the experiment. Staining mouse tissue with a mouse primary is the classic trap, and it needs a dedicated reagent system rather than an ordinary secondary.
3. Insist on cross adsorption for multiplexing. Cross adsorbed reagents have been passed over immunoglobulin from other species to remove antibodies that would bind them. In a two colour or two species experiment this is not an upgrade, it is a requirement.
4. Match the conjugate to the readout. Enzyme conjugates for chemiluminescent and chromogenic detection, fluorophores for multiplexed quantitation, biotin where amplification is needed and endogenous biotin has been blocked. The conjugate decides the imaging as much as the reagent does.
5. Titrate the secondary on your own samples. Excess secondary raises background faster than signal. Titration usually improves a blot or a section more than any change of primary, and it is a single plate or membrane of work.

The name contains the specification: anti human IgM antibody, Fab and subclass

Read a secondary reagent's name as a sentence: raised in this host, against this species, against this chain or fragment, adsorbed against these others, conjugated to this label. Every one of those fields changes behaviour, and most disappointing results come from ignoring one.

Where a supplier's name omits a field, the datasheet will have it. If neither does, that is itself informative about the reagent.

One anti human secondary antibody, many primaries

The practical economy in this area is standardising: one host, one adsorption specification, two or three conjugates, used across all the primaries in the laboratory. It reduces the number of titrations, makes protocols transferable and simplifies troubleshooting.

Keep the exception list short and explicit: the experiments where a different secondary is genuinely required, and why.

An anti-mouse igg hrp-linked antibody and the tissue problem

An anti-mouse igg hrp-linked antibody is the standard detection reagent for a mouse primary and is exactly the wrong reagent on mouse tissue, where it also detects the tissue's own immunoglobulin. The answers are a polymer kit designed for that pairing, a directly conjugated primary, or a primary from another host, and the artefact appears on a blot as bands at the immunoglobulin masses.

Common questions

What does cross adsorbed actually mean?

The reagent has been passed over immunoglobulin from other species so that antibodies binding those species are removed. It matters whenever more than one species is present in the experiment, including the tissue itself.

Can I stain mouse tissue with a mouse anti human antibody?

Only with a system designed for it, because an ordinary anti mouse secondary will bind the endogenous immunoglobulin throughout the tissue. Dedicated kits and directly conjugated primaries are the two workable routes.

HRP conjugated antibodies or a fluorophore conjugate?

Enzyme for maximum sensitivity on a single target, fluorophore for stable, quantitative and genuinely multiplexed detection. The choice follows the readout and the imager rather than the primary.

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