Researchers at the University of Salzburg measured the actual endotoxin in five commercial recombinant proteins with the LAL test, then asked whether levels near that ceiling could still move human immune cells.
One protein bought from two suppliers carried 140 picograms of endotoxin per microgram from the first and 2 picograms from the second, a 70-fold gap. Three of the five proteins held more than their data sheets stated. Human monocytes and dendritic cells released inflammatory signals at 0.02 nanograms per milliliter.
At that sensitivity, a protein used at 100 nanograms per milliliter can carry enough endotoxin to activate the cells under study. A stated ceiling said nothing about where a given product actually sat. The measured number showed a 70-fold difference between two products sold as the same protein.
Read the original study
Schwarz et al., PLOS ONE, 2014 · doi.org/10.1371/journal.pone.0113840
Below the limit is not one number.
Source
- Schwarz, H., Schmittner, M., Duschl, A., & Horejs-Hoeck, J. (2014). Residual endotoxin contaminations in recombinant proteins are sufficient to activate human CD1c+ dendritic cells. PLOS ONE, 9(12), e113840. https://doi.org/10.1371/journal.pone.0113840