Rules-Based Medicine

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Interleukin-21 (IL-21)

Ultrasensitive Immunoassay


Rules-Based Medicine’s internally developed and manufactured ultrasensitive immunoassay to interleukin-21 (IL-21) based on the Simoa® bead technology can accurately quantitate sub-pg/mL levels of IL-21 in human serum and plasma. The Simoa IL-21 assay is a valuable clinical research tool for pharmacodynamic analysis in several B and/or T cell modulated diseases, and its pleiotropic functions demonstrates its importance in autoimmune, oncology, and inflammatory diseases.

IL-21 is a type I cytokine and a member of the g chain (gc) family of cytokines. produced by various immune cells, including T follicular helper (Tfh) cells, CD4 and CD8 T cells, natural killer (NK) T cells, monocytes, macrophages, and dendritic cells. The IL-21 receptor is a heterodimer of IL-21R with the common gc, signaling through JAK1 and JAK3 and STAT3. IL-21 is a critical factor in Tfh and B cell interactions in the germinal center, and a potent stimulator of B cell proliferation, promotor of differentiation into plasma cells, and enhancer of antibody production. Additionally, IL-21 can also direct T cell differentiation, and enhance the cytotoxic activity of CD8 T cells and NK cells.


Swiss-Prot Accession Number: Q9HBE4

Alternate names for this biomarker include:


Simoa™ Services
Biomarker LLOQ*
(Serum and Plasma)
(Undiluted Samples)
Volume Required
Serum or plasma Other fluids**
Interleukin-21  (IL-21) 0.0053 pg/mL 0.00235 pg/mL 150 µL 150 µL

* Lower limit of quantitation (LLOQ) represents the lowest amount of an analyte that can be quantitatively determined with acceptable precision. LLOQ is determined by performing 2-fold serial dilutions of Standard to be tested in triplicate over three runs. The percent coefficient of variation (CV) is calculated for each of the dilution replicates, and the LLOQ is determined as the concentration at which the CV is 30%.

** Cerebrospinal fluid, urine, tissue culture supernatants,  bronchoalveolar lavage, synovial fluid, tissue extracts, tears, skin washings, etc.

All assay services are performed in our CLIA-certified laboratory.
Intended for Research Use Only.