LPS is biologically effective even in lowest concentrations (lower pg/ml range). They will be released during cell lyses but unlike enterotoxines or exotoxines they will not be continuously released in the culture media from living bacteria.
TLR4 is the receptor for LPS from Gram-negative bacteria. However, TLR4 alone is not sufficient to confer LPS responsiveness. TLR4 requires MD-2, a secreted molecule, to functionally interact with LPS. Furthermore, a third protein, called CD14, was shown to participate in LPS signalling, leading to NF-kB translocation. This signalling is mediated through the adaptor protein MyD88 but also through a MyD88-independent pathway that involves the (TIR) domain-containing adapter protein (TIRAP)4 5 6.
LPS & Cell culture
Endotoxins have, depending on the cell type and culture conditions, an influence on cell growth, cell differentiation, contractility and protein expression pattern. They trigger the release of tumor necrosis factor (TNF), Interleukins-1,6 and 8 and the production of Platelet-activating factors, Prostaglandin E2, Thromboxane A27 8 .
Today the LAL (Limulus Amebocyte Lysate) assay is used for the routine check of LPS in biological solutions. It was introduced on the market in the seventies and replaces more and more the rabbit pyrogenic test which was used since 1940. These tests were the first detection methods that had been certificated by the FDA.
In the meantime the humane full blood test (EAA, Endotoxin Activity Assay9)