Interleukin-21 plays a pivotal role in regulating T cell and B cell responses, making it a critical target for dissecting immune activation in cancer and autoimmune contexts. This recombinant protein demonstrates robust receptor engagement, binding human IL-21R with an EC50 of 16.65–19.49 ng/mL in functional ELISA and an affinity constant of 1.87 nM by surface plasmon resonance, providing quantitative benchmarks that support its use in cell-based proliferation assays with primary T cells, PBMCs, or TF-1 cells, as well as in JAK/STAT signaling pathway studies where dose-dependent responses are essential. Cross-reactivity with cynomolgus monkey IL-21R (EC50 15.01–19.43 ng/mL, KD 1.31 nM) enables direct translation to non-human primate models of tumor immunology or inflammatory disease. Expressed as the full mature protein sequence (aa 23–155) with C-terminal hFc1 tag in mammalian cells, the preparation meets purity thresholds above 90% and maintains endotoxin below 1.0 EU/μg, satisfying the stringent criteria required for immune cell functional assays where LPS contamination would confound cytokine-specific effects.
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