Microglia-Astrocyte Cooperation and Peripheral T Cells in Alzheimer's Disease: State-of-the-Art and Treatment Perspectives.

Alzheimer's disease (AD) is a neurodegenerative disorder first described more than one century ago. Over this time, many features of the disease have been discovered and, consequently, many different approaches in the diagnosis and treatment of AD have been developed. A major assumption has guided research on AD in the past: this fatal form of cognitive decline is believed to have a pathogenic basis in the deposition of amyloid beta (Aβ) aggregates throughout the brain. Consequently, a main goal of AD therapy is to reduce Aβ load, and several monoclonal antibodies targeting amyloid are among the most recent approaches to AD treatment. However, the effectiveness of these drugs is limited, as they cannot block the progression of the disease; they only slow it down in certain conditions. Many other causative factors are known to promote the development of the disease, with immune system involvement being the most investigated. Indeed, it has been well documented that the microglial response enhances the deposition of other altered proteins, such as Tau, and induces a neurotoxic microenvironment that promotes neuronal loss. In this scenario, the interaction between microglia and astrocytes is known to accelerate pathogenic processes, and a possible role for peripheral T lymphocytes in AD pathology has also been described. An interesting hypothesis is that immune cells driving chronic inflammation might worsen AD progression and, therefore, could represent a target for treatment strategies in this disease. Thus, this review article aims to summarise the role of brain and peripheral immune molecules and cells in AD. Also, immune-based treatments for AD are described, including those targeting microglia and T cells.