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 (Ab) 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 Ab(1–42). This was in contrast to exclusive TLR ligands lipopolysaccharide (LPS) (TLR4) and tripalmitoyl cysteinyl seryl tetralysine (Pam3CSK4) (TLR2). Atomic force microscopy imaging showed a fibrillar morphology for the proinflammatory Ab(1–42) species. Pretreatment of the cells with 10 lg/mL of a TLR2-specific antibody blocked 50% of the cell response to fibrillar Ab(1–42), completely blocked the Pam3CSK4 response, and had no effect on the LPS-induced response. A TLR4-specific antibody (10 lg/mL) blocked 35% of the cell response to fibrillar Ab(1–42), completely blocked the LPS response, and had no effect on the Pam3CSK4 response. Polymyxin B abolished the LPS response with no effect on Ab(1–42) ruling out bacterial contamination of the Ab samples. Combination antibody pretreatments indicated that neutralization of TLR2, TLR4, and CD14 together was much more effective at blocking the Ab(1– 42) response than the antibodies used alone. These data demonstrate that fibrillar Ab(1–42) can trigger the innate immune response and that both TLR2 and TLR4 mediate Abinduced tumor necrosis factor alpha production in a human monocytic cell line