Imrich Blasko

Lack of Antibody Production Following Immunization in Old Age: Association with CD8+CD28− T Cell Clonal Expansions and an Imbalance in the Production of Th1 and Th2 Cytokines

Although it is generally recognized that the function of the immune system declines with age, the nature of the underlying defects is still poorly understood. We now demonstrate the predominance of CD8+CD28− T cell clonal expansions in elderly persons who fail to produce specific Abs following influenza vaccination. These clones express effector cell markers and are mostly CD45RA+. When isolated and put into culture, they are unable to proliferate, but produce IFN-γ (but no IL-5) upon stimulation with anti-CD3 or autoantigen. These autoreactive CD8+ type 1 effector cells seem to trigger a Th1 polarization, as CD4+ T cells from elderly persons without in vivo Ab production produce Th1, but only low amounts of Th2 cytokines upon in vitro stimulation with PHA. Therefore, the increased occurrence of CD8+CD28− clonal expansions may be decisive for the development of immune deficiency in the elderly.

How chronic inflammation can affect the brain and support the development of Alzheimer's disease in old age: the role of microglia and astrocytes

A huge amount of evidence has implicated amyloid beta (Aβ) peptides and other derivatives of the amyloid precursor protein (βAPP) as central to the pathogenesis of Alzheimers disease (AD). It is also widely recognized that age is the most important risk factor for AD and that the innate immune system plays a role in the development of neurodegeneration. Little is known, however, about the molecular mechanisms that underlie age‐related changes of innate immunity and how they affect brain pathology. Aging is characteristically accompanied by a shift within innate immunity towards a pro‐inflammatory status. Pro‐inflammatory mediators such as tumour necrosis factor‐α or interleukin‐1β can then in combination with interferon‐γ be toxic on neurons and affect the metabolism of βAPP such that increased concentrations of amyloidogenic peptides are produced by neuronal cells as well as by astrocytes. A disturbed balance between the production and the degradation of Aβ can trigger chronic inflammatory processes in microglial cells and astrocytes and thus initiate a vicious circle. This leads to a perpetuation of the disease.

Experimental traumatic brain injury in rats stimulates the expression, production and activity of Alzheimer’s disease β-secretase (BACE-1)

Summary.Traumatic brain injury (TBI) is a risk factor for the development of Alzheimer’s disease (AD). After a traumatic brain injury depositions of amyloid beta (Aβ) in the brain parenchyma were found. In this study we investigated the expression pattern of β-secretase (BACE-1) in ipsi- or contralateral hippocampus and cortex following controlled cortical TBI in rats. BACE-1 mRNA levels, estimated by real time RT-PCR, were elevated 24 h post injury, and persisting up to 72 h, in the ipsi- and contralateral hippocampus and cerebral cortex as compared to the sham-treated animals (p<0.01). The TBI-induced changes in BACE-1 mRNA are due to enhanced hippocampal and cortical expression of BACE-1 mRNA in neurons and reactive astrocytes as revealed by in situ hybridization. The alterations in hippocampal BACE-1 mRNA levels are accompanied by corresponding increases in BACE-1 protein levels in ipsi- and contralateral hippocampus and ipsilateral cortex as demonstrated by Western blot analysis. In contrast, in the contralateral cortex only a weak increase of traumatically induced BACE-1 protein production was found. The activity of BACE-1 as measured by the formation of the cleavage product of amyloid beta precursor protein, transiently increased up to 48 h after injury, but returned to basal level 7 days post injury. This study demonstrates that the β-secretase is stimulated following TBI and may suggest a mechanism for the temporal increase of Aβ levels observed in patients with brain trauma.

Measurement of thirteen biological markers in CSF of patients with Alzheimer's disease and other dementias.

Cerebrospinal fluid (CSF) biological markers may be of valuable help in the diagnosis of dementia. The aim of the present study was to evaluate CSF levels of 13 potential biomarkers in patients with Alzheimer’s disease (AD), frontotemporal lobe dementia, alcohol dementia, major depression and control patients without any neuropsychiatric disease. The study was performed using β-amyloid 1–42 (Aβ42), total tau and phosphorylated tau-181 (P-tau181) as core markers. The ratio P-tau181/Aβ42 could significantly distinguish AD patients from all other diagnostic subgroups. CSF levels of 5 growth factors (HGF, GDNF, VEGF, BDNF, FGF-2) and 3 cytokines/chemokines (TNF-α, TGF-β1, MIP-1α) did not significantly differentiate between the studied groups. However, depending on the degree of neurodegeneration (as expressed by the ratio P-tau181/Aβ42), patients with AD displayed significantly increased CSF levels of nerve growth factor (NGF) as compared to healthy controls. CSF levels of monocyte chemoattractant protein 1 (MCP-1) were found to be significantly increased with age in all groups but did not distinguish AD patients from healthy controls. The results confirmed the suitability of the ratio P-tau181/Aβ42 for the diagnosis of AD, while CSF levels of NGF and MCP-1 are less specific and reliable for AD. It is suggested that the increase in NGF depends on the extent of neurodegeneration of the AD type and the increase in MCP-1 on age.

Conversion from cognitive health to mild cognitive impairment and Alzheimer's disease: Prediction by plasma amyloid beta 42, medial temporal lobe atrophy and homocysteine

The changes of plasma amyloid beta (Abeta42) protein, homocysteine and medial temporal lobe atrophy (MTA) were studied by the transition from cognitive health to mild cognitive impairment (MCI) and to Alzheimers disease (AD) in a prospective cohort of individuals aged 75 years. MTA but not plasma Abeta42 measured at baseline predicted which persons remained cognitively healthy (CH) and who developed AD 2.5 years later. The increase of plasma Abeta42 over time significantly distinguished between persons who remained CH on the one hand and MCI converters and AD converters out of cognitive health on the other (CH-to-MCI and CH-to-AD converters). Although both groups showed similar increase of Abeta42 levels, CH-to-AD converters had a higher increase of homocysteine compared to CH-to-MCI converters or to persons remaining CH. In comparison to all cognitive subgroups, the AD converters from MCI at baseline showed the smallest increase of Abeta42 levels and rather no increase of homocysteine. In logistic regression analysis, the increase of plasma Abeta42 but not change of MTA significantly predicted the conversion from CH to MCI, and changes of MTA and homocysteine but not of plasma Abeta42 predicted the conversion from CH to AD. The increase of plasma Abeta42 correctly allocated CH-to-MCI and CH-to-AD converters with low (63%) specificity (for both) and low (60%) sensitivity (54% for AD group). These results indicate that (1) plasma Abeta42 alone is not suitable as a biomarker for AD, (2) in the course of cognitive deterioration of the AD-type the increase of plasma Abeta42 seems to be an initial event, (3) similar to cerebrospinal fluid, changes of plasma Abeta42 may reflect the transition from cognitive health to AD, and (4) whether persons with MCI develop AD may depend on an accumulation of further toxic metabolites such as homocysteine.

Role of the Immune System in the Pathogenesis, Prevention and Treatment of Alzheimer's Disease

The dysregulation in the metabolism of β-amyloid precursor protein and consequent deposition of amyloid-β (Aβ) has been envisaged as crucial for the development of neurodegeneration in Alzheimer’s disease (AD). Amyloid deposition begins 10–20 years before the appearance of clinical dementia. During this time, the brain is confronted with increasing amounts of toxic Aβ peptides and data from the last decade intriguingly suggest that both the innate and the adaptive immune systems may play an important role in the disorder.Innate immunity in the brain is mainly represented by microglial cells, which phagocytose and degrade Aβ. As the catabolism of Aβ decreases, glial cells become overstimulated and start to produce substances that are toxic to neurons, such as nitric oxide and inflammatory proteins. Pro-inflammatory cytokines can be directly toxic or stimulate Aβ production and increase its cytotoxicity. A therapeutic possibility arises from clinical studies, which demonstrate that non-steroidal anti-inflammatory drugs (NSAIDs) may delay the onset and slow the progression of AD. Recent data show that in addition to the suppression of inflammatory processes in the brain NSAIDs may decrease the production of Aβ peptides.The role of adaptive immunity lies mainly in the fact that Aβ can be recognised as an antigen. Immunisation with Aβ peptides and peripheral administration of Aβ-specific antibodies both decrease senile plaques and cognitive dysfunction in murine models of AD. A recent trial in humans seems still to be hampered by adverse effects. As adaptive immunity decreases with aging while innate immunity remains intact, immunotherapy for AD will have to be adapted to this situation. Strategies that combine vaccination and inflammatory drug treatment could be considered.

Ibuprofen decreases cytokine-induced amyloid beta production in neuronal cells.

Trying to decrease the production of Amyloid beta (Abeta) has been envisaged as a promising approach to prevent neurodegeneration in Alzheimers disease (AD). A chronic inflammatory reaction with activated microglia cells and astrocytes is a constant feature of AD. The participation of the immune system in the disease process is further documented in several retrospective clinical studies showing an inverse relationship between the prevalence of AD and nonsteroidal anti-inflammatory drug (NSAID) therapy. Previously, we demonstrated that the combination of the proinflammatory cytokines TNFalpha with IFNgamma induces the production of Abeta-42 and Abeta-40 in human neuronal cells. In the present study, the neuronal cell line Sk-n-sh was incubated for 12 h with the cyclooxygenase inhibitor ibuprofen and subsequently stimulated with the cytokines TNFalpha and IFNgamma. Ibuprofen treatment decreased the secretion of total Abeta in the conditioned media of cytokine stimulated cells by 50% and prevented the accumulation of Abeta-42 and Abeta-40 in detergent soluble cell extracts. Viability of neuronal cells measured by detection of apoptosis was neither influenced by ibuprofen nor by cytokine treatment. The reduction in the production of Abeta by ibuprofen was presumably due to a decreased production of betaAPP, which in contrast to the control proteins M2 pyruvate kinase, beta-tubulin and the cytokine inducible ICAM-1 was detected at low concentration in ibuprofen treated cells. The data demonstrate a possible mechanism how ibuprofen may decrease the risk and delay the onset of AD.

Immunization with β-amyloid: could T-cell activation have a harmful effect?

We read with interest the comments of Karen Duff regarding the article by Schenk et al. on the prevention of Alzheimer’s disease (AD)-like pathology in the PDAPP-mouse by immunization with β-amyloid (Aβ)1xCuring amyloidosis: will it work in humans?. Duff, K. Trends Neurosci. 1999; 22: 485–486Abstract | Full Text | Full Text PDF | PubMed | Scopus (14)See all References, 2xImmunization with amyloid-beta attenuates Alzheimer-disease-like pathology in the PDAPP mouse. Schenk, D. et al. Nature. 1999; 400: 173–177Crossref | PubMed | Scopus (2477)See all References. We agree with most of the issues raised, but would like to make one additional point. According to recent research, human autoreactive lymphocytes can indeed recognize Aβ and might therefore be important for its elimination3xAPP peptides stimulate lymphocyte proliferation in normals, but not in patients with Alzheimer’s disease. Trieb, K. et al. Neurobiol. Aging. 1996; 17: 541–547Abstract | Full Text PDF | PubMedSee all References, 4xThe possible role of the immune system in Alzheimer’s disease. Marx, F. et al. Exp. Gerontol. 1998; 33: 871–881Crossref | PubMed | Scopus (39)See all References. This recognition mechanism seems impaired in individuals with AD, and, on the basis of these findings, the possibility has been raised that immunization against Aβ might prevent and treat AD in humans4xThe possible role of the immune system in Alzheimer’s disease. Marx, F. et al. Exp. Gerontol. 1998; 33: 871–881Crossref | PubMed | Scopus (39)See all References4. However, the likelihood that such immunization might lead to harmful side effects is of great concern. In particular, the consequences of T-lymphocyte activation after immune-system stimulation with Aβ.In the article by Schenk et al.2xImmunization with amyloid-beta attenuates Alzheimer-disease-like pathology in the PDAPP mouse. Schenk, D. et al. Nature. 1999; 400: 173–177Crossref | PubMed | Scopus (2477)See all References2, no information was provided on the exact nature of the immune response that occurs in mice. As expected for a peptide antigen, and confirmed by the presence of Aβ-reactive T cells, Aβ is certain to trigger T-cell activation and antibody production in humans. Aβ-reactive T cells might be part of a natural line of defence against the accumulation of Aβ, which is a toxic metabolite. Aβ-directed T-cell reactivity is relatively weak in healthy individuals3xAPP peptides stimulate lymphocyte proliferation in normals, but not in patients with Alzheimer’s disease. Trieb, K. et al. Neurobiol. Aging. 1996; 17: 541–547Abstract | Full Text PDF | PubMedSee all References3 and, therefore, unlikely to cause tissue damage. In order to achieve substantial antibody production after immunization, a much stronger T-cell response would have to be induced. This could be detrimental for several reasons. Aβ-specific T-cell lines contain a high percentage of CD8-positive cytotoxic T cells, which are capable of lysing cells that overproduce Aβ (Ref.5xTransfected human B cells: a new model to study the functional and immunostimulatory consequences of APP production. Marx, F. et al. Exp. Gerontol. 1999; 34: 783–795Crossref | PubMed | Scopus (13)See all ReferencesRef.5). When activated in vivo, these cells are likely to cause tissue damage in peripheral organs and in the brain, which they can enter as activated cells6xImmune reactivity in the nervous system: modulation of T-lymphocyte activation by glial cells. Wekerle, H. et al. J. Exp. Biol. 1987; 132: 43–57PubMedSee all References6. Cytokine production by T cells will presumably represent another problem, as Aβ-specific T cells produce a large amount of interferon γ (IFNγ; Ref. 5xTransfected human B cells: a new model to study the functional and immunostimulatory consequences of APP production. Marx, F. et al. Exp. Gerontol. 1999; 34: 783–795Crossref | PubMed | Scopus (13)See all ReferencesRef. 5). This cytokine triggers the production of Aβ40 and Aβ42 , in combination with tumour necrosis factor α (TNFα), and inhibits the secretion of soluble amyloid precursor proteins (APPs) by human neuronal and extraneuronal cells7xTNFalpha plus IFNgamma induce the production of Alzheimer beta-amyloid peptides and decrease the secretion of APPs. Blasko, I. et al. FASEB J. 1999; 13: 63–68PubMedSee all References7, thus completing a vicious circle. IFNγ can also be harmful in other respects, as it increases the production of TNFα and oxygen radicals by microglial cells after they have been stimulated with Aβ (Ref.8xActivation of microglial cells by beta-amyloid protein and interferon-gamma. Meda, L. et al. Nature. 1995; 374: 647–650Crossref | PubMedSee all ReferencesRef.8).For this and other reasons, great caution will be needed when immunization strategies against amyloidosis are designed for humans. It will have to be the goal of immunological interventions to achieve maximal clearance of the pathogen while minimizing side-effects, such as those caused by inappropriate T-cell activation. This might be achieved by the diversion of the immune response from a type 1 (IFNγ and TNFα) to a type 2 (interleukin 4) cytokine production pattern9xThe mechanism of in vitro T helper cell type 1 to T helper cell type 2 switching in highly polarized Leishmania major-specific T cell populations. Mocci, S. et al. J. Immunol. 1997; 158: 1559–1564PubMedSee all References9, the administration of certain Aβ epitopes that can stimulate those T cells that provide help to B cells (but no cytotoxic cells), or by similar responses. The success of a potentially revolutionary approach to prevent degenerative diseases might otherwise be endangered.

The possible role of the immune system in Alzheimer’s disease

Currently, there is little doubt that the immune system plays a role in the neurodegenerative process in Alzheimers disease (AD). Inflammatory proteins such as complement components, enzymes, eicosanoids, and cytokines are found in association with cerebral amyloid plaques and may exacerbate the fundamental pathology of AD, by stimulating Amyloid beta (A beta) production, supporting its aggregation and increasing its cytotoxicity. Activated microglia and astrocytes are the main source of these proteins, and A beta may trigger their release. Interestingly, there are also indications that the immune system may play a protective role against the development of AD. Microglial cells have been shown to degrade A beta, and recent evidence suggests that autoreactive A beta-specific T cells may be relevant to the elimination of the peptide. This mechanism seems, however, impaired in the majority of patients with AD. The immune system seems thus to represent a natural line of defense against the accumulation of dangerous amyloidogenic substances. Impairment of this specific immunological defense mechanism and the failure to eliminate a toxic metabolite can be the basis for a chronic nonspecific inflammatory process in the brain, as described above. AD is a good example how an immune response initially aiming at maintaining the integrity of the body may fail and consequently lead to tissue destruction and neuronal loss.

Plasma Amyloid Beta-42 Independently Predicts Both Late-Onset Depression and Alzheimer Disease

OBJECTIVES Depression in the elderly might represent a prodromal phase of Alzheimer disease (AD). High levels of plasma amyloid beta-42 (Aβ42) were found in prestages of AD and also in depressed patients in cross-sectional studies. This study examined the association of emerging late-onset depression (LOD) and AD with plasma Aβ42 in a sample of never depressed and not demented persons at baseline. DESIGN Prospective 5-year longitudinal study. PARTICIPANTS A community dwelling of older adults (N = 331) from the Vienna Transdanube Aging study. MEASUREMENTS Laboratory measurements, cognitive functioning, and depressive symptoms were assessed at baseline, 2.5, and 5 years follow-ups. RESULTS After exclusion of converters to AD, regression analysis revealed that higher plasma Aβ42 at baseline was a positive predictor for conversion to first episode of LOD. Independent of whether persons with mild cognitive impairment (MCI) at 2.5 years were included or excluded into regressions, higher plasma Aβ42 at baseline was a significant predictor for the development of probable or possible AD at 5 years. Higher conversion to AD was also associated with male gender but not with either higher scores on the Geriatric Depression Scale (GDS), with stroke or cerebral infarction nor apolipoprotein E ε4 allele. No association was found for an interaction between plasma Aβ42 levels and GDS. CONCLUSIONS Higher plasma Aβ42 at baseline predicted the development of first episode of LOD and conversion to probable or possible AD. Emerging depression as measured by scores on GDS at the 2.5-year follow-up, either alone or as an interaction factor with plasma Aβ42, failed to predict the conversion to AD at 5 years.