Recently, the term "inflammaging" was coined by Franceshci and colleagues to characterize a widely accepted paradigm that ageing is accompanied by a low-grade chronic up-regulation of certain proinflammatory responses. Inflammaging differs significantly from the traditional five cardinal features of acute inflammation in that it is characterized by a relative decline in adaptive immunity and Thelper 2 responses and is associated with increased innate immunity by cells of the mononuclear phagocyte lineage. While the over-active innate immunity characteristic of inflammaging may remain subclinical in many elderly individuals, a portion of individuals (postulated to have a "high responder inflammatory genotype") may shift from a state of "normal" or "subclinical" inflammaging to one or more of a number of age-associated diseases. We and others have found that IFN-γ and other pro-inflammatory cytokines interact with processing and production of Aβ peptide, the pathological hallmark feature of Alzheimer's disease (AD), suggesting that inflammaging may be a "prodrome" to AD. Although conditions of enhanced innate immune response with overproduction of pro-inflammatory proteins are associated with both healthy aging and AD, it is suggested that those who age "well" demonstrate anti-inflammaging mechanisms and biomarkers that likely counteract the adverse immune response of inflammaging. Thus, opposing the features of inflammaging may prevent or treat the symptoms of AD. In this review, we fully characterize the aging immune system. In addition, we explain how three novel treatments, (1) human umbilical cord blood cells (HUCBC), (2) flavanoids, and (3) Aβ vaccination oppose the forces of inflammaging and AD-like pathology in various mouse models.

Microglia are innate immune cells of myeloid origin that take up residence in the central nervous system (CNS) during embryogenesis. While classically regarded as macrophage-like cells, it is becoming increasingly clear that reactive microglia play more diverse roles in the CNS. Microglial "activation" is often used to refer to a single phenotype; however, in this review we consider that a continuum of microglial activation exists, with phagocytic response (innate activation) at one end and antigen presenting cell function (adaptive activation) at the other. Where activated microglia fall in this spectrum seems to be highly dependent on the type of stimulation provided. We begin by addressing the classical roles of peripheral innate immune cells including macrophages and dendritic cells, which seem to define the edges of this continuum. We then discuss various types of microglial stimulation, including Toll-like receptor engagement by pathogen-associated molecular patterns, microglial challenge with myelin epitopes or Alzheimer's β-amyloid in the presence or absence of CD40L co-stimulation, and Alzheimer disease "immunotherapy". Based on the wide spectrum of stimulus-specific microglial responses, we interpret these cells as immune cells that demonstrate remarkable plasticity following activation. This interpretation has relevance for neurodegenerative/neuroinflammatory diseases where reactive microglia play an etiological role; in particular viral/bacterial encephalitis, multiple sclerosis and Alzheimer disease.

Modulation of immune/inflammatory responses by diverse strategies including amyloid-beta (Abeta) immunization, nonsteroidal anti-inflammatory drugs, and manipulation of microglial activation states has been shown to reduce Alzheimer's disease (AD)-like pathology and cognitive deficits in AD transgenic mouse models. Human umbilical cord blood cells (HUCBCs) have unique immunomodulatory potential. We wished to test whether these cells might alter AD-like pathology after infusion into the PSAPP mouse model of AD. Here, we report a marked reduction in Abeta levels/beta-amyloid plaques and associated astrocytosis following multiple low-dose infusions of HUCBCs. HUCBC infusions also reduced cerebral vascular Abeta deposits in the Tg2576 AD mouse model. Interestingly, these effects were associated with suppression of the CD40-CD40L interaction, as evidenced by decreased circulating and brain soluble CD40L (sCD40L), elevated systemic immunoglobulin M (IgM) levels, attenuated CD40L-induced inflammatory responses, and reduced surface expression of CD40 on microglia. Importantly, deficiency in CD40 abolishes the effect of HUCBCs on elevated plasma Abeta levels. Moreover, microglia isolated from HUCBC-infused PSAPP mice demonstrated increased phagocytosis of Abeta. Furthermore, sera from HUCBC-infused PSAPP mice significantly increased microglial phagocytosis of the Abeta1-42 peptide while inhibiting interferon-gammainduced microglial CD40 expression. Increased microglial phagocytic activity in this scenario was inhibited by addition of recombinant CD40L protein. These data suggest that HUCBC infusion mitigates AD-like pathology by disrupting CD40L activity.

Human immunodeficiency virus (HIV)-1 infection of the central nervous system occurs in the vast majority of HIV infected patients. HIV-associated dementia (HAD) represents the most severe form of HIV-related neuropsychiatric impairment and is associated with neuropathology involving HIV proteins and activation of proinflammatory cytokine circuits. Interferon-γ (IFN-γ) activates the JAK/STAT1 pathway, a key regulator of inflammatory and apoptotic signaling, and is elevated in brains of HIV-1 infected brains progressing to HAD. Recent reports suggest that green tea derived (-)-epigallocatechin-3-gallate (EGCG) can attenuate neuronal damage mediated by this pathway in conditions such as brain ischemia. In order to investigate the therapeutic potential of EGCG to mitigate the neuronal damage characteristic of HAD, IFN-γ was evaluated for its ability to enhance well-known neurotoxic properties of HIV-1 proteins gp120 and Tat in primary neurons and mice. Indeed, IFN-γ enhanced the neurotoxicity of gp120 and Tat via increased JAK/STAT signaling. Additionally, primary neurons pretreated with a JAK1 inhibitor or those derived from STAT1-deficient mice were largely resistant to the IFN-γ enhanced neurotoxicity of gp120 and Tat. Moreover, EGCG treatment of primary neurons from normal mice reduced IFN-γ enhanced neurotoxicity of gp120 and Tat, while attenuating JAK/STAT1 pathway activation. EGCG was also found to attenuate the neurotoxic properties of HIV-1 proteins in the presence of IFN-γ in vivo. Taken together, these data suggest that EGCG attenuates the neurotoxicity of IFN-γ augmented neuronal damage from HIV-1 gp120 and Tat both in vitro and in vivo. Thus EGCG ‡

This therapeutic approach is clearly highly efficacious; however, the safety of this strategy has become an important concern. In a recent clinical trial, patients were administered a synthetic A␤ peptide (AN-1792) plus adjuvant, and Ϸ6% of these patients developed aseptic meningoencephalitis, most likely mediated by braininfiltrating activated T cells (3,4). This serious side effect led to suspension of the clinical trial. Furthermore, passive transfer of A␤ antibodies to transgenic AD mice results in cerebral microhemorrhage, a potentially adverse side effect (5, 6). Uncovering of these adverse events has redirected A␤ vaccination strategies toward the goal of developing an approach that is both safe and effective.Studies examining the brains of A␤-vaccinated patients developing meningoencephalitis implicate A␤-reactive T cell subsets as major components of this deleterious response to active A␤ vaccination (7, 8). To subvert possible meningoencephalitis resulting from A␤ vaccination, various strategies have been attempted. Interestingly, recent works suggest that A␤-derived peptides delivered intranasally (with adjuvant) to mucosal epithelial tissues results in effective clearance of A␤ plaques and improvement of cognitive function in animal models of AD. Moreover, T cell reactivity appeared to be considerably reduced compared with other active immunization strategies. In other studies, differential T cell responses depended on the epitope/fragment of A␤ peptide used for vaccination. Specifically, portions of the A␤ peptide seemed to stimulate different T cell responses, resulting in either proinflammatory T helper (Th) cell type 1 (Th1) responses or antiinflammatory Th cell type 2 (Th2) responses (9, 10). Such findings imply that A␤ vaccination is not only efficacious, but may also prove to be safe and therefore a feasible strategy for AD therapy depending on a number of factors, including route of delivery, adjuvant choice, and A␤ epitope administered.The skin is a well established effective route for vaccination, including delivery of peptide-based vaccines (11-13). Strong humoral and cellular immune responses have been elicited after transcutaneous (t.c.) vaccination (14), largely owing to the diverse populations of resident antigen-presenting cells (APCs) and other immune cells in the various dermal layers. Subsets of dermalresident Langerhans cell (LC) precursors, known as migratory CD14 ϩ LC precursors, are important immune regulators that demonstrate ''professional'' APC capability, including reducing T cell stimulatory function by producing antiinflammatory cytokines (15). Also, skin-resident keratinocytes release the antiinflammatory cytokine IL-10 in response to certain stimuli. Keratinocytederived IL-10 serves to buffer harmful proinflammatory immune activation and thereby preserves skin barrier integrity (16).Taken together, these lines of evidence led us to hypothesize that targeting A␤ immunotherapy to skin tissue might provide an immunotherapeutic approach that is both efficacious and safe. In...

Abnormalities in T-lymphocyte populations and function are observed in autism. Soluble amyloid precursor protein α (sAPP-α) is elevated in some patients with autism and is known to be produced by immune cells. In light of the well-established role of sAPP-α in proliferation, growth, and survival of neurons, we hypothesized an analogous role in the immune system. Thus, we explored whether sAPP-α could modulate immune development and function, especially aspects of the pinnacle cell of the adaptive arm of the immune system: the T cell. To do this, we generated mice overexpressing human sAPP-α and characterized elements of T-cell development, signal transduction, cytokine production, and innate/adaptive immune functions. Here, we report that transgenic sAPP-α-overexpressing (TgsAPP-α) mice displayed increased proportions of CD8(+) T cells, while effector memory T cells were decreased in the thymus. Overall apoptotic signal transduction was decreased in the thymus, an effect that correlated with dramatic elevations in Notch1 activation; while active-caspase-3/total-caspase-3 and Bax/Bcl-2 ratios were decreased. Greater levels of IFN-γ, IL-2, and IL-4 were observed after ex vivo challenge of TgsAPP-α mouse splenocytes with T-cell mitogen. Finally, after immunization, splenocytes from TgsAPP-α mice displayed decreased levels IFN-γ, IL-2, and IL-4, as well as suppressed ZAP70 activation, after recall antigen stimulation. Given elevated levels of circulating sAPP-α in some patients with autism, sAPP-α could potentially drive aspects of immune dysfunction observed in these patients, including dysregulated T-cell apoptosis, aberrant PI3K/AKT signaling, cytokine alterations, and impaired T-cell recall stimulation.

Amyloid-beta (Abeta) immunization efficiently reduces amyloid plaque load and memory impairment in transgenic mouse models of Alzheimer's disease (AD). Active Abeta immunization has also yielded favorable results in a subset of AD patients. However, a small percentage of patients developed severe aseptic meningoencephalitis associated with brain inflammation and infiltration of T-cells. We have shown that blocking the CD40-CD40 ligand (L) interaction mitigates Abeta-induced inflammatory responses and enhances Abeta clearance. Here, we utilized genetic and pharmacologic approaches to test whether CD40-CD40L blockade could enhance the efficacy of Abeta(1-42) immunization, while limiting potentially damaging inflammatory responses. We show that genetic or pharmacologic interruption of the CD40-CD40L interaction enhanced Abeta(1-42) immunization efficacy to reduce cerebral amyloidosis in the PSAPP and Tg2576 mouse models of AD. Potentially deleterious pro-inflammatory immune responses, cerebral amyloid angiopathy (CAA) and cerebral microhemorrhage were reduced or absent in these combined approaches. Pharmacologic blockade of CD40L decreased T-cell neurotoxicity to Abeta-producing neurons. Further reduction of cerebral amyloidosis in Abeta-immunized PSAPP mice completely deficient for CD40 occurred in the absence of Abeta immunoglobulin G (IgG) antibodies or efflux of Abeta from brain to blood, but was rather correlated with anti-inflammatory cytokine profiles and reduced plasma soluble CD40L. These results suggest CD40-CD40L blockade promotes anti-inflammatory cellular immune responses, likely resulting in promotion of microglial phagocytic activity and Abeta clearance without generation of neurotoxic Abeta-reactive T-cells. Thus, combined approaches of Abeta immunotherapy and CD40-CD40L blockade may provide for a safer and more effective Abeta vaccine.

Mutations in the presenilin-1 (PS1) gene are independent causes of familial Alzheimer's disease (AD). AD patients have dysregulated immunity, and PS1 mutant mice exhibit abnormal systemic immune responses. To test whether immune function abnormality caused by a mutant human PS1 gene (mhPS1) could modify AD-like pathology, we reconstituted immune systems of AD model mice carrying a mutant human amyloid precursor protein gene (mhAPP; Tg2576 mice) or both mhAPP and mhPS1 genes (PSAPP mice) with allo-geneic bone marrow cells. Here, we report a marked reduction in amyloid-β (Aβ) levels, β-amyloid plaques and brain inflammatory responses in PSAPP mice following strain-matched wild-type PS1 bone marrow reconstitution. These effects occurred with immune switching from pro-inflammatory T helper (Th) 1 to anti-inflammatory Th2 immune responses in the periphery and in the brain, which likely instructed microglia to phagocytose and clear Aβ in an ex vivo assay. Conversely, Tg2576 mice displayed accelerated AD-like pathology when reconstituted with mhPS1 bone marrow. These data show that haematopoietic cells bearing the mhPS1 transgene exacerbate AD-like pathology, suggesting a novel therapeutic strategy for AD based on targeting PS1 in peripheral immune cells.