While its toxic effects can be damaging, the sensing of lipid A by the human immune system may also be critical for the onset of immune responses to Gram-negative infection, and for the subsequent successful fight against the infection.ipid A (and LPS) has been demonstrated to activate cells via Toll-like receptor 4 (TLR4), MD-2 and CD14 on the cell surface (Poltorak, Beutler et al., Blood Cells Mol Dis 1998)(Beutler, Poltorak, J Endotoxin Res 2000)(Park et al., Nature 2009).