The dualistic nature of immune modulation in Alzheimer's disease: lessons from the transgenic models

There is extensive evidence that changes in immune system activation accompany the pathological changes of Alzheimer's disease (AD), but a mechanistic understanding of how the immune system actually participates in disease pathogenesis is still largely lacking. Because of the complexity of the immunological response, and the difficulty in identifying the key molecular players that underlie any given immunological response, expanding our understanding of the immunological response in AD beyond its descriptive stages has not been a straightforward exercise. The development of transgenic animals that form deposits of Abeta peptide in their brains has provided an unexpected dividend to those interested in the immunological response characterizing AD. Several of these transgenic models develop structures greatly resembling neuritic plaques, a hallmark feature of AD brain that is also a focal point of the immunological response occurring in AD. Genetic and pharmacological manipulation of these Abeta-depositing transgenic mice is providing some intriguing and unexpected insights into the role of innate and adaptive immune mechanisms in the pathogenesis of AD. This review will discuss immunological perspectives that have arisen from research using Abeta-depositing transgenic mice, and place these perspectives in the context of epidemiological and genetic studies that have previously suggested a role for the immune system in AD. The emerging story affirms the likely role of innate and adaptive immune mechanisms in the pathogenesis of AD, but provides a cautionary note as to the difficulties that are likely to face potential immunomodulatory therapies due to the dualistic beneficial and detrimental roles that immune mechanisms appear to play in AD.