Toll-like receptors 2 and 4 mediate Aβ(1-42) activation of the innate immune response in a human monocytic cell line

The primary molecules for mediating the innate immune response are the Toll-like family of receptors (TLRs). Recent work has established that amyloid-beta (A beta) fibrils, the primary components of senile plaques in Alzheimer's disease (AD), can interact with the TLR2/4 accessory protein CD14. Using antibody neutralization assays and tumor necrosis factor alpha release in the human monocytic THP-1 cell line, we determined that both TLR2 and TLR4 mediated an inflammatory response to aggregated A beta(1-42). This was in contrast to exclusive TLR ligands lipopolysaccharide (LPS) (TLR4) and tripalmitoyl cysteinyl seryl tetralysine (Pam(3)CSK(4)) (TLR2). Atomic force microscopy imaging showed a fibrillar morphology for the proinflammatory A beta(1-42) species. Pre-treatment of the cells with 10 mu g/mL of a TLR2-specific antibody blocked similar to 50% of the cell response to fibrillar A beta(1-42), completely blocked the Pam(3)CSK(4) response, and had no effect on the LPS-induced response. A TLR4-specific antibody (10 mu g/mL) blocked similar to 35% of the cell response to fibrillar A beta(1-42), completely blocked the LPS response, and had no effect on the Pam(3)CSK(4) response. Polymyxin B abolished the LPS response with no effect on A beta(1-42) ruling out bacterial contamination of the A beta samples. Combination antibody pre-treatments indicated that neutralization of TLR2, TLR4, and CD14 together was much more effective at blocking the A beta(1-42) response than the antibodies used alone. These data demonstrate that fibrillar A beta(1-42) can trigger the innate immune response and that both TLR2 and TLR4 mediate A beta-induced tumor necrosis factor alpha production in a human monocytic cell line.