Inflammasomes: NLRP3, Caspase-1 and IL-1
An inflammasome needs two signals, and they do different jobs. Signal one \u2014 TLR4 reading LPS, or TNF, or GM-CSF \u2014 licenses the cell to transcribe the inactive precursor of IL-1\u03b2. Signal two assembles the machine that cuts it. The two are routinely collapsed into one in summaries of this pathway, and almost every confusing result comes from that. The sensor at the centre, NLRP3, has no ligand at all: it is activated by potassium efflux, lysosomal rupture, mitochondrial damage and crystals \u2014 chemically unrelated stimuli that share only the property of indicating that something has gone wrong. What follows is one enzyme, caspase-1, doing three jobs: cutting pro-IL-1\u03b2, cutting pro-IL-18, and cutting gasdermin D, whose pores are simultaneously how the cytokine leaves and how the cell dies. Click any protein for the matching Assay Genie In Vivo antibody or ELISA kit.
Two signals, two jobs, and the difference matters experimentally. Priming through TLR4 and MyD88 does not build anything and does not release anything \u2014 it raises transcription of pro-IL-1\u03b2 and of NLRP3 itself. Activation is separate, and it is what assembles the sensor with ASC and pro-caspase-1 into a functional complex. A stimulus that only primes produces no IL-1\u03b2 at all; a stimulus applied to an unprimed cell produces none either. This is why nearly every published inflammasome experiment is a two-step protocol, and why a paper reporting IL-1\u03b2 from a single stimulus is usually reporting priming of cells that were already activated by something in the preparation.
NLRP3 has no ligand, and that is the point. Potassium efflux through P2X7, lysosomal rupture after crystal uptake, mitochondrial damage, and a long list of unrelated chemical insults all converge on it. The most economical reading is that NLRP3 reads cellular distress rather than any molecular pattern \u2014 which explains its involvement in gout, atherosclerosis, silicosis and type 2 diabetes, conditions with nothing microbial in common. NEK7 is the detail that makes this concrete: it is a mitotic kinase and a required NLRP3 partner, so a dividing cell cannot assemble an inflammasome. The other sensors are more conventional \u2014 NLRC4 reads flagellin through NAIP proteins, AIM2 binds cytosolic DNA directly, and caspase-4 binds intracellular LPS with no sensor in front of it at all.
Pyroptosis and cytokine release are the same mechanism. Caspase-1 cleaves gasdermin D, its N-terminal fragment oligomerises into a membrane pore, and IL-1\u03b2 \u2014 which has no signal peptide and cannot be secreted conventionally \u2014 leaves through it. Enough pores and the cell lyses. There is no switch between "release cytokine" and "die"; there is a dose. That also means a viability assay and a cytokine assay on this pathway are measuring two ends of one process, and treating them as independent read-outs overstates what has been shown. One further honesty: IL-1\u03b1 is active as its precursor and is released from necrotic cells without processing, so an IL-1 phenotype is not automatically an inflammasome phenotype.
The In Vivo tie-in, and where this map is thin. 14 of the 36 nodes carry a functional-grade antibody, and none of them is in the inflammasome itself. What is blockable is the output and the cell: IL-1\u03b2 and IL-1R1 are both functional grade, which is the one axis here that can be interrupted at ligand and receptor and the two answers compared; alongside them sit GM-CSF, TNF (ultra-low endotoxin, which is not a formality when LPS is the canonical priming stimulus), IL-10, TGF-\u03b2, the VivoGenie anti-IL-17A, and a complete cellular control panel of CD11b, Ly-6G (clone 1A8), CSF-1R, CD68, CD3 (145-2C11), CD4 (GK1.5) and CD8 (Ly-2). Stated plainly, the machine is research grade or ELISA throughout: NLRP3, NLRP1, NEK7, ASC, gasdermin D, HMGB1, S100A9 and TLR4 are research grade; NLRC4, AIM2, P2X7, caspase-1, caspase-4, IL-18, IL-18BP, IL-1Ra, MyD88 and S100A8 are ELISA only; and IL-1\u03b1, IL-6R and IL-23 are biosimilar. The practical design that follows is to block IL-1\u03b2 or IL-1R1, or remove the cell, and read assembly out through the ASC speck and caspase-1 activity \u2014 which is how most of the published work on this pathway is actually built. A last read-out caution: IL-18BP neutralises IL-18 with very high affinity, so free IL-18 rather than total IL-18 is what carries the biology, and a total-IL-18 assay alone will not distinguish them. For research use only; not for use in diagnostic or therapeutic procedures.
Every protein node links to a product — ELISA kit, In Vivo antibody or research antibody.