Interleukin-1β (IL-1β)

Interleukin-1 beta (IL-1β), encoded by the IL1B gene, is a pro-inflammatory cytokine of the interleukin-1 family and one of the principal drivers of fever and systemic inflammation. It is produced chiefly by activated macrophages, monocytes, and dendritic cells, and its release requires two separate signals. The first, typically a toll-like receptor engaging nuclear factor kappa B (NF-κB), transcribes an inactive 31 kDa precursor; the second assembles an inflammasome such as the NLRP3 inflammasome, which activates caspase-1 (CASP1) to cleave that precursor into the 17 kDa mature form. Because IL-1β carries no signal peptide it cannot leave by the classical secretory pathway, and can exit through Gasdermin D (GSDMD) pores in the plasma membrane among other unconventional pathways. This two-key arrangement is what keeps a cytokine this destructive from being released on transcription alone.

Mature IL-1β signals through IL-1R1 in complex with the accessory protein IL-1RAcP, recruiting MyD88 and the IRAK kinases to activate NF-κB and MAPK cascades. The transcriptional response includes further inflammatory mediators such as interleukin-6 and tumor necrosis factor alpha, and the enzymes that generate prostaglandins, notably cyclooxygenase-2 — IL-1β induces the machinery rather than the lipid mediators themselves. The system is restrained at several points: the receptor antagonist IL-1Ra occupies IL-1R1 without signaling, and the decoy receptor IL-1R2 binds the cytokine without transducing.

Sustained IL-1β production underlies chronic inflammatory and fibrotic disease, including rheumatoid arthritis, sepsis-associated organ injury, neurodegeneration, metabolic disease, and diabetic complications, and it works within a network alongside TNF, Interleukin-6 (IL-6), and Interleukin 18 (IL-18). Blockade is clinically established rather than prospective: recombinant IL-1Ra, an IL-1β-neutralizing antibody, and a soluble receptor trap are used in the hereditary autoinflammatory syndromes, where the response is near-complete, and in gout and adult-onset Still disease. Trial evidence that IL-1β blockade lowers recurrent cardiovascular events independently of lipid lowering established inflammation itself as a treatable cardiovascular target. Measurement of the cytokine — in serum, urine, or tissue homogenates — may serve as a pharmacodynamic or diagnostic biomarker in selected contexts, though its short half-life and low circulating concentrations limit routine use.