Interleukins are the most frequently used recombinant cytokines in immunology — but IL-2 expressed in E. coli behaves differently from IL-2 produced in mammalian cells, and a His-tagged IL-6 may give you different results than a tag-free format in a sensitive bioassay. This selection guide walks through the four decisions that determine assay success: species, expression system, tag format, and bioactivity data — with a quick-reference decision table and application matrix.
What Is a Recombinant Interleukin?
Interleukins (ILs) are a family of cytokines — small secreted signaling proteins, typically 12–35 kDa, that mediate communication between immune cells. Each interleukin binds specific receptor complexes to activate intracellular pathways such as JAK-STAT, MAPK, and PI3K/AKT. Key members include IL-2 (T cell and NK cell growth factor), IL-6 (inflammation and B cell differentiation), IL-10 (immunosuppression), and IL-17 (neutrophil recruitment).
Recombinant interleukins are produced in E. coli, yeast, insect, or mammalian expression systems, with purity typically greater than 90% by SDS-PAGE. BioCrest Sci offers 325+ recombinant interleukins across all major families, from human, mouse, rat, and 50+ species.
Selection Decision Table
| Your research scenario | Recommended format | Why |
|---|---|---|
| Cell proliferation / functional assay (T cells, NK cells) | Active protein, verified ED50 | Bioactivity is the critical parameter — always request ED50 data |
| Sensitive primary cell culture | Low endotoxin (<1 EU/μg) | Endotoxin independently activates TLR4 and confounds readouts |
| ELISA / Western Blot | E. coli, His-tagged | Cost-effective; tag enables easy detection and purification |
| In vivo studies | Carrier-free, endotoxin-tested | Avoid carrier protein interference in animal models |
| SPR / BLI binding kinetics | Avi-tagged or Fc-tagged | Site-specific immobilization with defined orientation |
| Long-term stability required | Lyophilized powder | 12-month shelf life at -20°C to -80°C |
1. Match the Species to Your Model
Always match the recombinant interleukin to your experimental system. Human interleukins do not reliably activate mouse receptors — human IL-2, for example, binds the mouse IL-2 receptor with markedly reduced affinity. For mouse in vivo models, use mouse interleukins; for human primary cells and cell lines, use human. Cross-species work with primate models generally uses human or cynomolgus proteins.
BioCrest Sci provides interleukins from 50+ species, including human, mouse, rat, rabbit, dog, pig, and cynomolgus monkey.
2. Choose the Expression System
| System | Best for | Limitations |
|---|---|---|
| E. coli | Non-glycosylated ILs (IL-2, IL-4, IL-6); ELISA/WB; bulk production | No glycosylation; may require refolding for disulfide-rich cytokines |
| Yeast | Secreted cytokines with moderate PTM needs | Glycosylation differs from mammalian patterns |
| Mammalian (HEK293/CHO) | Cell-based bioassays, in vivo work, glycosylated targets (IL-1R, IL-6R) | Higher cost, longer lead times |
For quantitative immunoassays, E. coli-derived interleukins are usually sufficient. For functional cell-based work where receptor binding depends on native folding, choose mammalian-expressed active proteins.
3. Pick the Right Tag — or Go Tag-Free
His-tag: small (6-10 residues), rarely interferes with ELISA or Western Blot; the default choice for detection workflows.
Fc-tag: extends serum half-life, enables easy detection with anti-Fc secondary antibodies; preferred for SPR immobilization and in vivo studies.
Avi-tag: site-specific biotinylation for streptavidin-based capture (SPR, BLI, tetramers).
Tag-free: eliminates any risk of tag interference in sensitive functional assays; recommended for receptor-binding studies where the N-terminus is involved.
4. Verify Purity, Bioactivity, and Endotoxin
Three parameters matter beyond the spec sheet:
- Purity: greater than 90% by SDS-PAGE is the minimum for reproducible assays; check whether the stated purity is from SDS-PAGE or HPLC (HPLC values are typically higher for the same material)
- Bioactivity (ED50): for functional assays, request ED50 values from cell proliferation assays (e.g., CTLL-2 for IL-2). A protein can be >95% pure but biologically inactive
- Endotoxin: for primary cell cultures, use <1 EU/μg; for routine ELISA, <10 EU/mg is generally acceptable
Interleukins by Application — Quick Reference
| Application | Common Interleukins |
|---|---|
| T cell expansion (CAR-T research) | IL-2, IL-7, IL-15 |
| NK cell culture | IL-2, IL-15, IL-21 |
| Th17 differentiation | IL-6, IL-23, IL-1β (with TGF-β) |
| Treg studies | IL-2, IL-10, TGF-β |
| Inflammation models | IL-1β, IL-6, TNF-α |
| B cell differentiation | IL-4, IL-6, IL-21 |
Handling and Storage
- Centrifuge the vial briefly before opening to collect lyophilized material at the bottom
- Reconstitute in sterile water or buffer to 0.1–1.0 mg/mL
- Aliquot immediately — avoid repeated freeze-thaw cycles (bioactivity drops after 2–3 cycles)
- Store lyophilized protein at -20°C to -80°C (12-month shelf life); store working aliquots at 4°C for up to one week
FAQ
Can I use E. coli-expressed IL-2 in T cell culture?
Yes — IL-2 is not glycosylated, and E. coli-expressed active IL-2 with a verified ED50 works well in T cell and NK cell expansion protocols.
What endotoxin level do I need for primary cells?
Use <1 EU/μg. Endotoxin activates TLR4 on macrophages and dendritic cells, confounding cytokine readouts in primary cultures.
Does the His-tag interfere with bioactivity?
Generally not for ELISA or Western Blot. For receptor-binding or sensitive functional assays, consider tag-free formats.
Can I request a specific buffer or concentration?
Yes — BioCrest Sci supports custom formulation, concentration, and bulk lot reservation. Contact sales@biocrestsci.com with your requirements.
References
- Boyman O, Sprent J. The role of interleukin-2 during homeostasis and activation of the immune system. Nat Rev Immunol. 2012;12(3):180-90.
- Waldmann TA. The biology of interleukin-2 and interleukin-15: implications for cancer therapy and vaccine design. Nat Rev Immunol. 2006;6(8):595-601.
- Brenner D, Blaser H, Mak TW. Regulation of tumour necrosis factor signalling: live or let die. Nat Rev Immunol. 2015;15(6):362-74.
By BioCrest Sci Research Team. Last reviewed August 2026.
Explore the complete collection at the Interleukins resource hub or browse all 325 recombinant interleukins. Need help selecting? Contact sales@biocrestsci.com.