The older brain, inflammation, vaccination and the prevention of dementia

Abstract

SummaryAn important protective function of the brain's innate immune system is to detect the presence of proteins such as amyloid and to remove them before they become neurotoxic, as is thought to occur in Alzheimer's disease (AD). Ageing affects the immune system response to infection and can influence the systemic response to vaccination and other potential immunotherapeutic agents. The generation of systemic antibodies is a vital component of the immune response, facilitating the identification and clearance of pathogens from the central nervous system (CNS). Experimental evidence using transgenic animal models of AD has shown successful clearance of amyloid from the CNS following vaccination with an amyloid peptide, and consequently a trial of amyloid beta peptide (Aβ) vaccination was undertaken in older people with AD. This produced some unexpected results, as not only was there evidence for amyloid plaque removal, but also a small number of cases developed encephalitis. A detailed review of the response to vaccination and the neuropathology findings are discussed, showing that the findings are understandable given the effects of ageing upon the innate immune system in the brain. Finally, the therapeutic potential of manipulating the regulatory components of the ageing innate immune system in order to inhibit brain inflammation and reduce cognitive decline is outlined.