Humoral immunity in brain aging and Alzheimer's disease

Microglia and inflammation: impact on developmental brain injuries

Inflammation during the perinatal period has become a recognized risk factor for developmental brain injuries over the past decade or more. To fully understand the relationship between inflammation and brain development, a comprehensive knowledge about the immune system within the brain is essential. Microglia are resident immune cells within the central nervous system and play a critical role in the development of an inflammatory response within the brain. Microglia are critically involved with both the innate and adaptive immune system, regulating inflammation and cell damage within the brain via activation of Toll-like receptors, production of cytokines, and a myriad of other intracellular and intercellular processes. In this article, microglial physiology is reviewed along with the role of microglia in developmental brain injuries in humans and animal models. Last, microglial functions within the innate and adaptive immune system will be summarized. Understanding the processes of inflammation and microglial activation is critical for formulating effective preventative and therapeutic strategies for developmental brain injuries.

Alzheimer's disease and Helicobacter pylori infection: Defective immune regulation and apoptosis as proposed common links

Although degenerative diseases of the central nervous system, including Alzheimer's disease (AD), have an increasingly high impact on aged population their association with Helicobacter pylori (H. pylori) infection has not as yet been thoroughly researched. Current H. pylori infection appears to induce irregular humoral and cellular immune responses that, owing to the sharing of homologous epitopes (molecular mimicry), cross-react with components of nerves, thereby contributing and possibly perpetuating the apoptotic neural tissue damage observed in neurodegenerative diseases including AD. An association between AD and H. pylori infection has been recently addressed by two studies. A higher seropositivity for anti-H. pylori immunoglobulin G antibodies in 30 patients with AD than in 30 age-matched controls was reported in one study; this serological test, however, has limitations because it does not discriminate between current and old infections. In the other study, by introducing the histological method (the actual gold standard) for diagnosis of H. pylori infection, we reported a higher prevalence of H. pylori infection in 50 AD patients than in 30 anemic controls. This pathogen may influence the pathophysiology of AD by promoting platelet and platelet-leukocyte aggregation; releasing various pro-inflammatory and vasoactive substances; developing cross-mimicry with host antigens; producing reactive oxygen metabolites and circulating lipid peroxides; influencing the apoptotic process; and increasing, through induction of atrophic gastritis, homocysteine, which contributes to vascular disorders implicated in endothelial damage and neurodegeneration.

Alzheimer's disease, brain immune privilege and memory: a hypothesis

The most distinctive feature of Alzheimer's disease (AD) is the specific degeneration of the neurons involved in memory consolidation, storage, and retrieval. Patients suffering from AD forget basic information about their past, loose linguistic and calculative abilities and communication skills. Thus, understanding the etiology of AD may provide insights into the mechanisms of memory and vice versa. The brain is an immunologically privileged site protected from the organism's immune reactions by the blood-brain barrier (BBB). All risk factors for AD (both cardiovascular and genetic) lead to destruction of the BBB. Evidence emerging from recent literature indicates that AD may have an autoimmune nature associated with BBB impairments. This hypothesis suggests that the process of memory consolidation involves the synthesis of novel macromolecules recognized by the immune system as "non-self" antigens. The objective of this paper is to stimulate new approaches to studies of neural mechanisms underpinning memory consolidation and its breakdown during AD. If the hypothesis on the autoimmune nature of AD is correct, the identification of the putative antigenic macromolecules might be critical to understanding the etiology and prevention of AD, as well as for elucidating cellular mechanisms of learning and memory.