Dementia is an increasing health problem in older aged populations worldwide. Age-related
changes in the brain can be observed decades before the first symptoms of cognitive decline appear.
Cognitive impairment has chronic inflammatory components, which can be enhanced by systemic immune
activation. There exist mutual interferences between inflammation and cognitive deficits. Signs of
an activated immune system i.e. increases in the serum concentrations of soluble biomarkers such as
neopterin or accelerated tryptophan breakdown along the kynurenine axis develop in a significant proportion
of patients with dementia and correlate with the course of the disease, and they also have a predictive
value. Changes in biomarker concentrations are reported to be associated with systemic infections
by pathogens such as cytomegalovirus (CMV) and bacterial content in saliva. More recently, the
possible influence of microbiome composition on Alzheimer’s disease (AD) pathogenesis has been
observed. These observations suggest that brain pathology is not the sole factor determining the pathogenesis
of AD. Interestingly, patients with AD display drastic changes in markers of immune activation
in the circulation and in the cerebrospinal fluid. Other data have suggested the involvement of factors
extrinsic to the brain in the pathogenesis of AD. However, currently, neither the roles of these factors
nor their importance has been clearly defined.
Keywords: Alzheimer's dementia, Cognitive impairment, Cytomegalovirus, Kynurenine axis, Microbiome, Neopterin, Pathogenesis.
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