Lymphopenia in primary degenerative dementia

Low levels of peripheral blood activated and senescent T cells characterize people with HIV-1-associated neurocognitive disorders

Background

HIV infection induces a 75% increase in the risk of developing neurocognitive impairment (NCI), which has been linked to immune activation. We therefore looked for immune activation markers correlating with NCI.

Method

Sixty-five people aged 55-70 years living with controlled HIV-1 infection were enrolled in the study and their neurocognitive ability was assessed according to the Frascati criteria. Fifty-nine markers of T4 cell, T8 cell, NK cell, and monocyte activation, inflammation and endothelial activation were measured in their peripheral blood. White matter hyperintensities (WMH) were identified by magnetic resonance imaging. Double hierarchical clustering was performed for the activation markers and 240 patients including the 65 whose neurocognitive performance had been evaluated.

Results

Thirty-eight percent of volunteers presented NCI. Twenty-four percent of them were asymptomatic and fourteen percent had a mild disorder. Strikingly, activated (HLA-DR+) as well as senescent (CD57+CD28-CD27±) T4 cells and T8 cells were less prevalent in the peripheral blood of participants with NCI than in participants without the disorder. Accordingly, the percentage of HLA-DR+ T4 cells was lower in volunteers with periventricular and deep WMH. The double hierarchical clustering unveiled six different immune activation profiles. The neurocognitive performances of participants with two of these six profiles were poor. Here again, these two profiles were characterized by a low level of T4 and T8 cell activation and senescence.

Conclusion

Our observation of low circulating levels of activated and senescent T cells in HIV-1 patients with NCI raises the interesting hypothesis that these lymphocytes may be recruited into the central nervous system.

Association of B cell profile and receptor repertoire with the progression of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent type of dementia. Reports have revealed that the peripheral immune system is linked to neuropathology; however, little is known about the contribution of B lymphocytes in AD. For this longitudinal study, 133 participants are included at baseline and second-year follow-up. Also, we analyze B cell receptor (BCR) repertoire data generated from a public dataset of three normal and 10 AD samples and perform BCR repertoire profiling and pairwise sharing analysis. As a result, longitudinal increase in B lymphocytes is associated with increased cerebral amyloid deposition and hyperactivates induced pluripotent stem cell-derived microglia with loss-of-function for beta-amyloid clearance. Patients with AD share similar class-switched BCR sequences with identical isotypes, despite the high somatic hypermutation rate. Thus, BCR repertoire profiling can lead to the development of individualized immune-based therapeutics and treatment. We provide evidence of both quantitative and qualitative changes in B lymphocytes during AD pathogenesis.

Association of peripheral immunity with cognition, neuroimaging, and Alzheimer's pathology

Background

Neuroinflammation has been considered to be a driving force of Alzheimer’s disease. However, the association between peripheral immunity and AD has been rarely investigated.

Methods

Separate regression analyses were conducted to explore the associations among peripheral immune markers and cognition, neuroimaging, and AD pathology. Causal mediation analyses were used to investigate whether the associations with cognition were mediated by AD pathology.

Results

A total of 1107 participants (43.9% female, mean age of 73.2 years) from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) were included. Regression analyses indicated that elevated neutrophils (NEU) count and neutrophil-lymphocyte ratio (NLR) were associated with lower levels of global cognition, memory function (MEM), and executive function (EF), and reduced brain metabolism by 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) as well as greater ventricular volume. An elevated NLR was associated with a lower level of β-amyloid (Aβ) and a higher level of total tau (T-tau) in cerebrospinal fluid (CSF), smaller hippocampal volume (HV), and lesser entorhinal cortex (EC) thickness. On the contrary, an elevated level of lymphocytes (LYM) was associated with a higher level of Aβ and a lower level of T-tau in CSF, better cognition, and less atrophy of brain regions (ventricular volume, HV, and EC thickness). The associations of LYM and NLR with cognition were mediated by Aβ and T-tau pathology (proportion: 18%~64%; p < 0.05).

Conclusions

We revealed that two types of peripheral immune cells (NEU and LYM) and the ratio of these two cell types (NLR) had associations with cognition, neuroimaging, and AD pathology. The associations might be mediated by Aβ and tau pathology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-00968-y.

Intact circadian rhythm despite cortisol hypersecretion in Alzheimer's disease: A meta-analysis

Hypersecretion of the glucocorticoid steroid hormone cortisol by individuals with Alzheimer's disease (AD) has been suspected for several decades, during which time dozens of examinations of this phenomenon have been conducted and published. The goals of this investigation were to summarize this sizeable body of literature, test whether participant and methodological characteristics modify the magnitude of the AD-associated basal cortisol hypersecretion, and examine whether cortisol circadian rhythmicity is maintained among individuals with AD. To this end, the present meta-analysis and systematic review examined over 300 comparisons of indices of basal HPA-axis functioning between individuals with AD and cognitively normal older adults. AD was associated with basal cortisol elevations (g = 0.45) but the magnitude of the effect was not systematically impacted by any of the participant characteristics considered or the time-of-day of the cortisol sampling. Further, there was no evidence of group differences among direct indices of circadian rhythmicity such as the cortisol awakening response or the diurnal cortisol slope. These results suggest that basal hypersecretion of cortisol, but not circadian dysrhythmia, is characteristic of individuals with AD. Mechanistically, the observed hypersecretion is consistent with the theorized AD-driven deterioration of the hippocampus and subsequent reduction in hypothalamic-pituitary-adrenal axis inhibition. Further investigation is warranted to elucidate the role and timing of cortisol elevations in the progression of AD.

Dysregulation of Systemic Immunity in Aging and Dementia

Neuroinflammation and the tissue-resident innate immune cells, the microglia, respond and contribute to neurodegenerative pathology. Although microglia have been the focus of work linking neuroinflammation and associated dementias like Alzheimer's Disease, the inflammatory milieu of brain is a conglomerate of cross-talk amongst microglia, systemic immune cells and soluble mediators like cytokines. Age-related changes in the inflammatory profile at the levels of both the brain and periphery are largely orchestrated by immune system cells. Strong evidence indicates that both innate and adaptive immune cells, the latter including T cells and B cells, contribute to chronic neuroinflammation and thus dementia. Neurodegenerative hallmarks coupled with more traditional immune system stimuli like infection or injury likely combine to trigger and maintain persistent microglial and thus brain inflammation. This review summarizes age-related changes in immune cell function, with special emphasis on lymphocytes as a source of inflammation, and discusses how such changes may potentiate both systemic and central nervous system inflammation to culminate in dementia. We recap the understudied area of AD-associated changes in systemic lymphocytes in greater detail to provide a unifying perspective of inflammation-fueled dementia, with an eye toward evidence of two-way communication between the brain parenchyma and blood immune cells. We focused our review on human subjects studies, adding key data from animal models as relevant.

Immunological functioning in Alzheimer's disease: differential effects of relative left versus right temporoparietal dysfunction

The cerebral hemispheres are differentially involved in regulating immunological functioning and the neuropathology associated with Alzheimer's disease (AD) is asymmetrical. Thus, subgroups of AD patients may exhibit different patterns of immunological dysfunction. We explored this possibility in a group of AD patients and found that patients with low white blood cell counts and low lymphocyte numbers exhibited better performance on tests of right temporoparietal functioning. Also, a significant positive relationship exists between lymph numbers and performance on a test of left temporoparietal functioning. Thus, some AD patients have greater immunological dysfunction based on relative left versus right temporoparietal functioning.

Can peripheral leukocytes be used as Alzheimer's disease biomarkers?

Alzheimer's disease (AD) is the leading cause of dementia in elderly populations throughout the world and its incidence is on the rise. Current clinical diagnosis of AD requires intensive examination that includes neuropsychological testing and costly brain imaging techniques, and a definitive diagnosis can only be made upon postmortem neuropathological examination. Additionally, antemortem clinical AD diagnosis is typically administered following onset of cognitive and behavioral symptoms. As these symptoms emerge relatively late in disease progression, therapeutic intervention occurs after significant neurodegeneration, thereby limiting efficacy. The identification of noninvasive diagnostic biomarkers of AD is becoming increasingly important to make diagnosis more widely available to clinics with limited access to neuropsychological testing or state-of-the-art brain imaging, reduce the cost of clinical diagnosis, provide a biological measure to track the course of therapeutic intervention, and most importantly, allow for earlier diagnosis--possibly even during the prodromal phase--with hopes of therapeutic intervention prior to appreciable neurodegeneration. Circulating leukocytes are attractive candidate AD biomarkers as they can be obtained in a minimally invasive manner and are easily analyzed by widely available flow cytometry techniques. In this review, we critically analyze the potential utility of peripheral leukocytes as biological markers for AD.

The effect of citalopram on gene expression profile of Alzheimer lymphocytes

Antidepressants are widely used in the treatment of mood disorders associated with dementia, however little information is available on their effect at the molecular level. In certain neurodegenerative disorders, such as in Alzheimer's disease, lymphocytes have been used to assess mirror changes that thought to occur in the brain. Gene expression profiles of lymphocytes from Alzheimer patients have been shown to differ from that seen with controls. To address this issue in light of antidepressant treatment, we used lymphocytes derived from Alzheimer's disease patients and control individuals to assess the impact of the selective serotonine reuptake inhibitor citalopram on gene expression using a cDNA microarray representing 3200 distinct human genes. Sequences that are differentially regulated after treatment with citalopram were identified and categorized based on similarities in biological functions. This analysis revealed that the overexpression of genes in control and Alzheimer white blood cells by citalopram are implicated in cell survival. Apart from this, citalopram did not markedly alter genes involved in other molecular functions in control cells. In contrast, alteration of genes implicated in ionic currents, cell-adhesion, immune mechanism, and adrenergic functions, were also observed in Alzheimer lymphocytes. The expression of genes of Alzheimer lymphocytes by citalopram is modulated differently which may correlate with the pathology.

Peripheral blood lymphocyte subset distribution and function in patients with Alzheimer's disease and other dementias

BACKGROUND

Until recently, new data on immune aspects of Alzheimer's disease (AD) have suggested that some facets of AD pathogenesis may be immune related. However, the effects of dementia itself on immune function have not been considered.

AIM

To compare the distribution of peripheral blood lymphocyte subsets and their function in patients with AD and other dementias.

METHODS

Peripheral blood lymphocyte numbers, T cell subset distribution, proliferative responses to mitogens and suppressor cell assay were studied in a well characterised group of patients with AD, and compared to patients with other forms of dementia. Age and sex matched elderly controls were screened to exclude dementia, and young controls were medical, paramedical and laboratory staff. Analysis of variance (ANOVA) and student's test were used for statistical analysis.

RESULTS

The CD8+ lymphocyte population was reduced in AD and in other forms of dementia, when compared with non-demented elderly and young controls. Concanavalin A induced lymphocyte transformation was reduced in all dementia groups and in elderly compared with young controls. The changes in T cell numbers and function were not specific for Alzheimer's disease, but were found also in other forms of dementia.

Distribution of peripheral lymphocytes in Alzheimer patients and controls

Deficient immunoregulation has been postulated to play a role in the pathogenesis of Alzheimer's dementia. Recently, lymphopenia was reported to be more prevalent in Alzheimer patients than in control subjects. In addition, a decreasing number of total lymphocytes was found to be significantly correlated with increasing severity of dementia. In an attempt to replicate these findings, we studied 55 Alzheimer patients and 41 healthy controls of comparable age and gender, but found no significant difference in the distribution of total lymphocytes between these groups. Furthermore, total lymphocytes were not significantly correlated with dementia severity. Our findings, therefore, do not lend further support to an immune hypothesis for Alzheimer's dementia.