Recombinant Human IL-6 Protein

What it means: This IL-6 is produced in Human cells rather than in E. coli or insect cells. The manufacturer states the host as human cells and does not name a specific cell line for this product.

Why it matters:

• IL-6 is a glycosylated cytokine; expression in human cells supports mammalian glycosylation.
• Production in a human host avoids bacterial host-cell contaminants that can affect immune-cell cultures.
• Together with the animal-free, xeno-free and tag-free manufacturing format, it suits fully human culture systems.

How to interpret here: An expression system of Human cells means the IL-6 was made and glycosylated by a human cell line, consistent with its use on human B cells, myeloid cells, progenitors and hepatocyte models.

Tip: When switching from an IL-6 made in another host, re-titrate the working dose rather than assuming the same activity per microgram.

What it means: The protein is Tag-free: no His, Fc, GST or other affinity tag is fused to the IL-6 sequence, and no tag needs to be removed before use.

Why it matters:

• A tag adds extra amino acids that can change folding, receptor binding, stability or the apparent molecular weight of a small signaling protein.
• In defined culture media every added component is a variable; a tag-free protein keeps the ligand as close as possible to the native sequence.
• Tag-free proteins are also preferred when results will be compared with published protocols that used untagged proteins.

How to interpret here: Tag-free here means the vial contains only the IL-6 protein. It cannot be captured or detected with anti-His, anti-GST or Protein A reagents, so plan detection with an antibody against IL-6 itself.

What it means: Purity of >95% by SDS-PAGE means that when the protein is run on a denaturing gel and stained, at least 95% of the stained protein is the IL-6 band. It is the purity specification stated by the manufacturer for this product.

Why it matters:

• High purity limits other proteins in the vial that could act on cells or interfere with downstream readouts.
• Dosing is done by protein mass, so a pure preparation makes the amount of IL-6 added more accurate and comparable between experiments.
• The purity specification sits alongside an endotoxin limit of <0.5 EU/µg and a cell-based activity test.

How to interpret here: A specification of >95% by SDS-PAGE is a minimum value. The exact result for each lot is on the Certificate of Analysis (CoA), available from BioHippo on request.

Tip: SDS-PAGE purity shows how clean the preparation is, not how active it is; check the activity data separately.

What it means: The species is Human: the amino-acid sequence is that of human IL-6 (interleukin-6). The protein is also produced in human cells, so both the sequence and the expression host are human.

Why it matters:

• Matching the species of the protein to the species of the cells avoids differences in receptor affinity between species.
• Human sequence is the usual choice for work with human B cells, myeloid cells, hematopoietic progenitors and hepatocyte models.
• Recording the species in protocols matters because the same protein is sold from several species by many suppliers.

How to interpret here: Human here refers to the protein sequence. When reproducing a published protocol, check that the protocol also used Human IL-6; if it used a protein from another species, the working concentration may need adjusting.

What it means: The protein is supplied Lyophilized, that is freeze-dried to a powder, from a 0.2 µm-filtered solution in PBS and without carrier protein.

Why it matters:

• Lyophilized protein is more stable during storage than a solution, which gives a long shelf life when stored correctly.
• The stock concentration is chosen at reconstitution, so it can be matched to the volumes used in the protocol.
• As supplied, store at −20°C to −80°C for up to 12 months from receipt; after reconstitution keep it under sterile conditions at 2°C to 8°C for up to 1 month or at −20°C to −80°C for up to 3 months; a manual-defrost freezer is recommended.

How to interpret here: Lyophilized means the vial must be reconstituted before use: briefly centrifuge the vial before opening, then reconstitute in sterile PBS containing 0.1% endotoxin-free recombinant human serum albumin, mix gently and prepare single-use aliquots.

Tip: Avoid repeated freeze–thaw cycles of the reconstituted protein; prepare single-use aliquots.

What it means: 26–30 kDa is the molecular weight given by the manufacturer. Separately, the manufacturer describes the protein as a glycosylated monomer.

Why it matters:

• Molecular weight is the first check of identity when the protein is run on a gel or analysed by other methods.
• Band position depends on gel conditions, such as reducing or non-reducing sample buffer, so these conditions should be recorded when comparing results.
• The manufacturer gives this as a nominal value and refers to lot-level documentation for exact data.

How to interpret here: This is the value stated by the manufacturer. Refer to the lot-specific Certificate of Analysis (CoA), available from BioHippo on request, for the data that apply to each lot.

Tip: If a gel band differs from this value, compare it with the CoA for that lot and note whether the sample was reduced or non-reduced.

What it means: Activity is tested by TF-1 cell proliferation: IL-6 is added to human TF-1 cells and stimulation of proliferation is measured.

Why it matters:

• A cell-based test confirms that the protein is functionally active, which purity alone cannot show.
• The assay depends on IL-6 receptor and gp130 signaling, the same route studied in JAK/STAT3 experiments.
• Because the TF-1 cells are human, the assay tests the human cytokine on a human receptor system.

How to interpret here: TF-1 cell proliferation shows that the protein signals through its receptor complex. The manufacturer does not give a numerical EC50, so working concentrations must be set by protocol and dose response.

Tip: Lot-specific release values are on the Certificate of Analysis, available from BioHippo on request.