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

Abstract

The primary molecules for mediating the innate immune response are the Toll‐like family of receptors (TLRs). Recent work has established that amyloid‐beta (Aβ) 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 Aβ(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 Aβ(1–42) species. Pre‐treatment of the cells with 10 μg/mL of a TLR2‐specific antibody blocked ∼50% of the cell response to fibrillar Aβ(1–42), completely blocked the Pam3CSK4 response, and had no effect on the LPS‐induced response. A TLR4‐specific antibody (10 μg/mL) blocked ∼35% of the cell response to fibrillar Aβ(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 Aβ(1–42) ruling out bacterial contamination of the Aβ samples. Combination antibody pre‐treatments indicated that neutralization of TLR2, TLR4, and CD14 together was much more effective at blocking the Aβ(1–42) response than the antibodies used alone. These data demonstrate that fibrillar Aβ(1–42) can trigger the innate immune response and that both TLR2 and TLR4 mediate Aβ‐induced tumor necrosis factor alpha production in a human monocytic cell line.

Active Immunization with Amyloid-β 1–42 Impairs Memory Performance through TLR2/4-Dependent Activation of the Innate Immune System

“…By activating TLR2, Ab induces the secretion of proinflammatory molecules like TNF, IL-6, and IL-1b in mouse primary microglia (23). Similarly, both TLR2 and -4 mediate Ab 1-42 -induced proinflammatory responses in human monocytic cell lines (48). In contrast, TLR2 and -4 are not required for the induction of EAE by active immunization with myelin Ags emulsified in CFA.…”

Activation of innate immunity by lysozyme fibrils is critically dependent on cross-β sheet structure

“…These bacterial fibrils activate TLR2, and the process proved to be fibril-specific [52]. Aβ fibrils trigger the expression of TNF-α through a mechanism involving activation of TLR2 and TLR4, but non-fibrillar Aβ does not [52,53].…”

IL-1 Blockade Attenuates Islet Amyloid Polypeptide-Induced Proinflammatory Cytokine Release and Pancreatic Islet Graft Dysfunction

“…Both CD36-induced TLR4-TLR6 heterodimer formation (53) and TLR2 activation (27,54) have also been implicated in the response to Ab. We found hIAPP-induced TNF-a release from macrophages to be largely MyD88 dependent.…”