Recombinant Human HSP60 Produced in ClearColi™ BL21(DE3) Does Not Activate the NFκB Pathway

HSP60, an intracellular molecular chaperone has been largely described as an alarmin or damage-associated molecular pattern when released outside the cell. HSP60 has been reported as a possible ligand of TLR2 or TLR4 inducing NFκB-dependant signaling pathway leading to cytokine secretion. However, recent publications suggested that HSP60 could not act as an activator of TLR4 by itself. The observed effect could be due to the presence of endotoxin in HSP60 preparation especially LPS. In order to clarify the controversy, we produced recombinant human HSP60 in two different strains of Escherichia coli, standard strain for protein overproduction, BL21(DE3), and the new ClearColi BL21(DE3) strain which lacks LPS-activity through TLR4. Undoubtedly, we have shown that recombinant HSP60 by itself was not able to induce NFκB-dependant signaling pathway in a model of THP1 monocyte cell line. Our data suggest that HSP60 needs either pathogen-associated molecules, specific post-translational modification and/or other host factors to activate immune cells via NFκB activation.