A complex proinflammatory role for peripheral monocytes in Alzheimer's disease

Area of Science:

• Neuroimmunology
• Alzheimer's Disease Pathogenesis
• Innate and Adaptive Immunity

Background:

• Alzheimer's disease (AD) is characterized by amyloid-beta (Aβ) plaque accumulation due to impaired microglial function.
• Monocytes/macrophages (M/M) are recruited to the brain in AD, potentially aiding in Aβ clearance.
• The specific role and phenotype of M/M in AD pathogenesis require further elucidation.

Purpose of the Study:

• To investigate the characteristics and functional profile of M/M in patients with AD and mild cognitive impairment (MCI).
• To explore the involvement of M/M in immune responses and Aβ processing within the context of AD.
• To identify potential therapeutic targets related to M/M function in AD.

Main Methods:

• Analysis of M/M phenotypes in AD, MCI, and healthy control (HC) individuals.
• Aβ42-stimulated cell cultures to assess M/M inflammatory markers and receptor expression.
• Confocal microscopy to visualize M/M-Aβ interactions and MHC-II complex formation.
• Quantification of toll-like receptor (TLR) and cytokine expression in M/M.

Main Results:

• Increased percentages of inflammatory M/M (CD14+ CD16-CCR2++CX3CR1low) expressing TLR2, TLR4, IL-6, and CCR2 were observed in AD patients.
• Evidence suggests M/M in AD present Aβ42 peptides complexed with MHC-II.
• Elevated levels of TLR3- and TLR8-expressing, IL-23-producing M/M were found in both AD and MCI patients compared to HC.

Conclusions:

• M/M in AD exhibit a distinct inflammatory phenotype, contributing to disease pathology.
• M/M activation via TLRs suggests a role in initiating innate immune responses in AD.
• M/M may participate in adaptive immunity by presenting Aβ peptides, potentially influencing AD progression.
• Targeting M/M-mediated inflammatory pathways and Aβ presentation could be a viable therapeutic strategy for AD.