Endotoxin-free heat-shock protein 70 fails to induce APC activation

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Abstract
Previous work has suggested that the peptide‐carrier, heat‐shock protein (hsp)70, could directly activate APC. Here we show that this ability is related to endotoxin contamination of the humanrhsp70 produced in Escherichia coli. Hence, the ability of 1–3 μg/ml of rhsp70 to induce the maturation of human monocyte‐derived DC is abrogated in the presence of the LPS‐antagonist polymyxin B or when the rhsp70 contains less than 60 IU/mg endotoxin. Such a level of contamination of the rhsp70 is, however, sufficient — in the presence of soluble rCD14, the LPS co‐receptor — toinduce cytokine secretion from monocytes and DC, despite the presence of polymyxin B. However, when endotoxin contamination is below 10 IU/mg, rhsp70 does not induce cytokine secretion — even in the presence of soluble rCD14 — or activate p38 mitogen‐activated protein kinase signaling pathways, thus showing that an "endotoxin free" hsp70 does not activate APC.

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