What is Low Endotoxin FBS?

Why does endotoxin in FBS matter?

Endotoxin (lipopolysaccharide, LPS) is a highly potent immune activator. At concentrations as low as 0.1 EU/mL, LPS activates TLR4 signalling in sensitive cell types — triggering NF-κB nuclear translocation and transcription of pro-inflammatory genes. In standard FBS at 10%, cells in culture are continuously exposed to LPS at concentrations (0.1–1 EU/mL in the medium) that chronically activate these pathways.

When is low endotoxin FBS required?

• Drug screening targeting NF-κB, inflammatory pathways, or innate immunity: endotoxin background inflates apparent IC50
• AAV viral vector production in HEK293T: endotoxin reduces transfection efficiency and vector yield
• Cytokine ELISA and multiplex assays: endotoxin creates non-specific background cytokine signal
• Hepatocyte-based CYP induction assays: endotoxin suppresses baseline CYP3A4 expression
• iPSC differentiation with cytokine-driven protocols: endotoxin competes with defined growth factor signalling

Key Facts

• Endotoxin (LPS) is a component of gram-negative bacterial cell walls — present in standard FBS as a processing contaminant
• Standard FBS endotoxin: 1–10 EU/mL. Low endotoxin FBS: <1 EU/mL (tested by LAL chromogenic assay)
• LPS activates TLR4 → NF-κB → pro-inflammatory cytokine expression (IL-6, TNF-α, IL-1β) in monocytes, macrophages, hepatocytes and many other cell types
• In drug screening, endotoxin-driven NF-κB activation can increase apparent IC50 values by 3–10× for compounds targeting inflammatory pathways
• In AAV production (HEK293T), endotoxin activates antiviral interferon pathways that reduce transfection efficiency and AAV yield
• In cytokine multiplex assays, endotoxin creates non-specific cytokine background that masks treatment effects
• SeamlessBio FBS Low Endotoxin is tested to <1 EU/mL by LAL chromogenic assay on every lot

Further Reading

• What is FBS?
• AAV Viral Vector Production — FBS Guide
• Cytotoxicity Assays — FBS Selection Guide
• In Vitro Drug Metabolism — Matrix Guide

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