Detecting a pathway that only exists once it fires: why a caspase 1 antibody has to distinguish the cleaved active enzyme from the pro-form, what a gsdmd antibody reports about pyroptosis that a viability assay cannot, how an nlrp3 antibody, an asc antibody, an aim2 antibody and a nod1 antibody each report assembly rather than abundance, where a ninj1 antibody, an mlkl antibody, a ripk3 antibody and a rip3 antibody mark membrane rupture and necroptosis instead, what a tlr4 antibody, a tlr3 antibody, a dectin-1 antibody and a langerin antibody detect at the sensing end, how an il-1 beta antibody, the il 1 beta antibody sold under the spaced spelling and an il-18 antibody must be read as precursor and mature forms, and why a cgas antibody, a sting antibody, a tbk1 antibody, an irf3 antibody, a pkr antibody, a zbp1 antibody, an ifit1 antibody, an ifitm3 antibody, a gbp2 antibody, a trex1 antibody, an adar1 antibody and a dhx9 antibody belong to the same sample handling problem

Choosing reagents for a pathway that fires

1. Buy against the cleaved form, not the gene. An enzyme that circulates as an inactive precursor is only informative once cleaved. Reagents raised against the neoepitope exposed by cleavage answer the activation question; reagents against the parent detect both forms and are useful only as a loading reference.
2. Read assembly as redistribution, not as amount. Adaptor and sensor proteins signal by forming specks and filaments. Their total abundance may not change at all, so imaging the distribution, or a native gel, tells you what a denaturing blot cannot.
3. Preserve the state at lysis. Proteolysis continues in a lysate and phosphorylation is stripped within minutes. Inhibitors have to be in the buffer before the cells meet it, samples kept cold and processing kept short, or the pathway will look inactive whatever it was doing.
4. Measure the secreted product as well as the cell. Mature cytokines leave the cell, so a lysate blot can miss the output entirely. Pair the cellular readout with a supernatant measurement, and be explicit about which form the assay detects.
5. Control with a stimulus and an inhibitor. A treatment that fires the pathway and one that blocks it bracket every experiment. Without them a band cannot be distinguished from a background, and a negative result cannot be distinguished from a failed stimulation.

The reagent has to match the event

Every step in these pathways is a change of state rather than a change of amount: a cleavage, a phosphorylation, an oligomerisation, a translocation. That makes the choice of reagent unusually consequential, because most catalogue antibodies are raised against the protein rather than against the state.

Read the immunogen and the stated specificity before buying, and where a cleaved form is the question, confirm the supplier shows the cleaved band separately from the precursor.

Handling is the commonest failure

Warm handling, a missing protease inhibitor and a long time between plate and denaturation lose more signal in this area than any reagent choice. The pathway continues to run in the dish while the experiment is being collected.

Fix one lysis protocol for pathway work, make the buffer fresh with inhibitors, date it, and record it with the result. It removes an entire class of irreproducibility.

Common questions

Why does my caspase blot show only the precursor?

Either the pathway did not fire, or the cleaved product left with the supernatant, or the cleavage was reversed during handling. Blot the supernatant as well as the lysate and check the inhibitor cocktail was in the buffer before lysis.

Can abundance report inflammasome activation?

No. Assembly is the activation event and it does not require new protein. Imaging speck formation, or a native separation, is what reports it; a denaturing blot of total protein does not.

Which controls make these results credible?

A known stimulus, a specific inhibitor, and where possible cells lacking the sensor. Reduction of signal in the knockout is the strongest evidence a reagent is reporting what its label claims.

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