Infection in Alzheimer's disease

  • Rebecca Montacute

Student thesis: Phd


Infections are a common co-morbidity in Alzheimer's disease (AD), and evidence suggests that infections can exacerbate neuroinflammation and increase cognitive decline in AD patients. In AD, immune changes are observed both in the central nervous system (CNS) and in the rest of the body. However, only a few studies have investigated immune responses to infection in AD. Here, two extensively studied infections, Toxoplasma gondii (T. gondii) and Trichuris muris (T. muris) were used to investigate infection in AD. T. gondii is a protozoan parasite which is common globally, including in the developed world where AD cases are increasing dramatically. Infection with T. gondii starts in the gut, before becoming systemic and then infecting the CNS, where the parasite forms a chronic cyst infection. In contrast, T. muris is a nematode parasite, which remains localised to the gut. Notably, T. gondii is known to alter neuroinflammation and behaviour. T. gondii forms cysts preferentially in the areas of the brain commonly affected by AD, such as the hippocampus, which therefore makes it an interesting model to study co-morbidity. AD is often associated with advanced age. As we age, our immune system declines, and an important unanswered question is whether age impacts on the immune response to infection. This is of particular significance when considering chronic infections such as T. gondii, which require immune surveillance to prevent parasite recrudescence. Therefore, the aim of this thesis was to investigate infection in AD by determining: whether the immune response to an infection is altered in AD; whether the immune response to an infection in AD differs with age; what the effects of infection are on neuroinflammation, pathology and behaviour in AD; what are the effects of chronic infection with T. gondii. Immune responses to infection were altered in both the 3xTg-AD and the APP PS1 mouse models of AD, including increased inflammation and weight loss in AD mice following infection. Although older (eleven to twelve-month-old) 3xTg-AD mice showed some alterations in cytokine responses following infection, overall there were no major difference compared to younger (five to six-month-old) animals. Additionally, infection was found to alter neuroinflammation in both 3xTg-AD and APP PS1 mice, though differently. In 3xTg-AD mice, microglia activation increased following infection with T. gondii and T. muris, showing that infection did not need to be in the brain to alter neuroinflammation. In APP PS1 mice, a decrease in microglia activation occurred after infection with T. gondii, which was accompanied by an increase in IL-1alpha production and increased amyloid beta levels in APP PS1 mice following infection. However, no changes were found in behaviour following infection with T. gondii or T. muris in AD mouse models. Finally, chronic T. gondii infection was investigated in the TgF344-AD rat, which was established as a suitable AD model with both amyloid and tau pathology in which to study chronic infection. This work adds to a growing body of literature to suggest that infections are detrimental to AD patients, and that future measures to decrease morbidity could focus on further study of infections in AD, and the development of strategies to better prevent infections in AD patients.
Date of Award1 Aug 2017
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorStuart Allan (Supervisor), Catherine Lawrence (Supervisor) & Sheena Cruickshank (Supervisor)


  • infection
  • neuroinflammation
  • trichuris muris
  • toxoplasma gondii
  • Alzheimer's disease

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