Studies carried out during the last few decades have consistently shown that cell surface MHC class I (MHC-I) molecules are endowed with functions unrelated with antigen presentation. These include ...cis–trans-interactions with inhibitory and activating KIR and LILR, and cis-interactions with receptors for hormones, growth factors, cytokines, and neurotransmitters. The mounting body of evidence indicates that these non-immunological MHC-I functions impact clinical and biomedical settings, including autoimmune responses, tumor escape, transplantation, and neuronal development. Notably, most of these functions appear to rely on the presence in hematopoietic and non-hematopoietic cells of heavy chains not associated with β2m and the peptide at the plasma membrane; these are known as open MHC-I conformers. Nowadays, open conformers are viewed as functional cis-trans structures capable of establishing physical associations with themselves, with other surface receptors, and being shed into the extracellular milieu. We review past and recent developments, strengthening the view that open conformers are multifunctional structures capable of fine-tuning cell signaling, growth, differentiation, and cell communication.
Antigen-driven human effector-memory CD8+ T cells expressing low levels of the CD8β chain have been previously described. However, little is known on a possible antigen-independent trigger. We have ...examined the impact that IL-15 has on the expression of CD8β on purified human naïve CD8+ T cells after CFSE labeling and culture with IL-15. As expected, IL-15 induced naïve CD8+ T cells to proliferate and differentiate. Remarkably, the process was associated with a cell-cycle dependent down-modulation of CD8β from the cell surface, leading to the generation of CD8αβ low and CD8αβ − (i.e., CD8αα) T cells. In contrast, expression of the CD8α chain remained steady or even increased. Neither IL-2 nor IL-7 reproduced the effect of IL-15. Determination of mRNA levels for CD8α and CD8β isoforms by qPCR revealed that IL-15 promoted a significant decrease in mRNA levels of the CD8β M-4 isoform, while levels of the M-1/M-2 isoforms and of CD8α increased. Noteworthy, CD8+ T cell blasts obtained after culture of CD8+ T cells with IL-15 showed a cell-cycle dependent increase in the level of the tyrosine kinase Lck, when compared to CD8+ T cells at day 0. This study has shown for the first time that IL-15 generates CD8αα + αβ low and CD8αα + αβ − T cells containing high levels of Lck, suggesting that they may be endowed with unique functional features.
Understanding the rationale for the generation of a pool of highly differentiated effector memory CD8
T cells displaying a weakened capacity to scrutinize for peptides complexed with major ...histocompatibility class I molecules
their T cell receptor, lacking the "signal 2" CD28 receptor, and yet expressing a highly diverse array of innate receptors, from natural killer receptors, interleukin receptors, and damage-associated molecular pattern receptors, among others, is one of the most challenging issues in contemporary human immunology. The prevalence of these differentiated CD8
T cells, also known as CD8
CD28
, CD8
KIR
, NK-like CD8
T cells, or innate CD8
T cells, in non-lymphoid organs and tissues, in peripheral blood of healthy elderly, namely centenarians, but also in stressful and chronic inflammatory conditions suggests that they are not merely end-of-the-line dysfunctional cells. These experienced CD8
T cells are highly diverse and capable of sensing a variety of TCR-independent signals, which enables them to respond and fine-tune tissue homeostasis.
There is increasing evidence that in humans the adaptive immunological system can influence cognitive functions of the brain. We have undertaken a comprehensive immunological analysis of lymphocyte ...and monocyte populations as well as of HLA molecules expression in a cohort of elderly volunteers (age range, 64-101) differing in their cognitive status. Hereby, we report on the identification of a novel signature in cognitively impaired elderly characterized by: (1) elevated percentages of CD8+ T effector-memory cells expressing high levels of the CD45RA phosphate receptor (Temra
); (2) high percentages of CD8+ T cells expressing high levels of the CD8β chain (CD8β
); (3) augmented production of IFNγ by
activated CD4+ T cells. Noteworthy, CD3+CD8+ Temra
and CD3+CD8β
cells were associated with impaired cognition. Cytomegalovirus seroprevalence showed that all volunteers studied but one were CMV positive. Finally, we show that some of these phenotypic and functional features are associated with an increased frequency of the HLA-B8 serotype, which belongs to the ancestral haplotype HLA-A1, Cw7, B8, DR3, DQ2, among cognitively impaired volunteers. To our knowledge, this is the first proof in humans linking the amount of cell surface CD45RA and CD8β chain expressed by CD8+ Temra cells, and the amount of IFNγ produced by
activated CD4+ T cells, with impaired cognitive function in the elderly.
The choroid plexus (CP) is part of the blood‐cerebrospinal fluid barrier (BCSFB) and was recently described as an important component of the circadian clock system. It is the principal source of ...cerebrospinal fluid (CSF) and responsible for the synthesis and secretion of various neuroprotective peptides including those involved in amyloid‐β (Aβ) transport/degradation, contributing to Aβ homeostasis. Inadequate Aβ metabolic clearance and transport across the BCSFB have been associated with circadian dysfunctions in Alzheimer's disease (AD) patients. To investigate whether AD pathology influences Aβ scavengers circadian expression, we collected CP at different time points from an AD mouse model (APP/PS1) (female and male animals, aged 6‐ and 12‐months‐old) and analyzed their mRNA expression by Real‐time RT‐PCR. Only angiotensin‐converting enzyme (Ace) expression in 6‐month‐old female wild‐type mice and transthyretin (Ttr) expression in 12‐month‐old female wild‐type mice presented significant rhythmicity. The circadian rhythmicity of Ace and Ttr, prompt us to analyze the involvement of circadian rhythm in Aβ uptake. A human CP papilloma (HIBCPP) cell line was incubated with Aβ‐488 and uptake was evaluated at different time points using flow cytometry. Aβ uptake displayed circadian rhythmicity. Our results suggest that AD might affect Aβ scavengers rhythmicity and that Aβ clearance is a rhythmic process possibly regulated by the rhythmic expression of Aβ scavengers.
Alzheimer's phenotype, sex and age affect the expression of Amyloid‐β scavengers. Amyloid‐β scavengers such as angiotensin‐converting enzymes show circadian rhythmicity in the choroid plexus of female 6‐month‐old mice. This rhythmicity is impaired in Alzheimer's disease animal models or in choroid plexus epithelial cells treated with Amyloid‐β. Amyloid‐β uptake by the choroid plexus epithelial cells displays circadian rhythmicity.
MHC class I molecules regulate brain development and plasticity in mice and HLA class I molecules are associated with brain disorders in humans. We investigated the relationship between ...plasma‐derived soluble human HLA class I molecules (sHLA class I), HLA class I serotypes and dementia. A cohort of HLA class I serotyped elderly subjects with no dementia/pre‐dementia (NpD, n = 28), or with dementia (D, n = 28) was studied. Multivariate analysis was used to examine the influence of dementia and HLA class I serotype on sHLA class I levels, and to compare sHLA class I within four groups according to the presence or absence of HLA‐A23/A24 and dementia. HLA‐A23/A24 and dementia, but not age, significantly influenced the level of sHLA class I. Importantly, the concurrent presence of HLA‐A23/A24 and dementia was associated with higher levels of sHLA class I (p < 0.001). This study has shown that the simultaneous presence of HLA‐A23/HLA‐A24 and dementia is associated with high levels of serum sHLA class I molecules. Thus, sHLA class I could be considered a biomarker of neurodegeneration in certain HLA class I carriers.
Polycythemia vera (PV) is a myeloproliferative neoplasm characterized by overproduction of red blood cells. We have performed a comprehensive characterization of blood immune cells for expression of ...naïve and memory receptors as well as β
2
m-associated and β
2
m-free MHC class I heavy chains, also known as closed and open conformers, respectively, in PV patients and age-matched controls (CTR). We show that the peripheral CD3
+
CD8
+
T cell pool in PV patients is clearly divided into two discrete populations, a more granular CD3
+
CD8
high
T cell population enriched in effector-memory CD45RA
+
T cells (CD8
+
T
EMRA
) when compared to CTR (
P
< 0.001), and a less granular CD3
+
CD8
int
T cell population that is completely absent in the CTR group (78 vs. 0%,
P
< 0.001) and is a mixture of naïve (CD8
+
T
N
) and CD8
+
T
EMRA
cells expressing intermediate levels of CD28, i.e., CD3
+
CD8
int
CD28
int
. While the percentage of CD3
+
CD8
int
T
N
cells correlated positively with the number of erythrocytes, the percentage of CD3
+
CD8
int
T
EMRA
correlated negatively with the number of platelets. Finally, we report that PV patients’ lymphocytes and monocytes display lower levels of closed (W6/32
+
) MHC-I conformers at the cell surface while exhibiting increased amounts of open (HC-10
+
) MHC-I conformers. The implications of this distinctive immune signature are discussed.
Abstract
The choroid plexus (CP) is part of the blood‐cerebrospinal fluid barrier (BCSFB) and was recently described as an important component of the circadian clock system. It is the principal ...source of cerebrospinal fluid (CSF) and responsible for the synthesis and secretion of various neuroprotective peptides including those involved in amyloid‐β (Aβ) transport/degradation, contributing to Aβ homeostasis. Inadequate Aβ metabolic clearance and transport across the BCSFB have been associated with circadian dysfunctions in Alzheimer's disease (AD) patients. To investigate whether AD pathology influences Aβ scavengers circadian expression, we collected CP at different time points from an AD mouse model (APP/PS1) (female and male animals, aged 6‐ and 12‐months‐old) and analyzed their mRNA expression by Real‐time RT‐PCR. Only angiotensin‐converting enzyme (Ace) expression in 6‐month‐old female wild‐type mice and transthyretin (Ttr) expression in 12‐month‐old female wild‐type mice presented significant rhythmicity. The circadian rhythmicity of Ace and Ttr, prompt us to analyze the involvement of circadian rhythm in Aβ uptake. A human CP papilloma (HIBCPP) cell line was incubated with Aβ‐488 and uptake was evaluated at different time points using flow cytometry. Aβ uptake displayed circadian rhythmicity. Our results suggest that AD might affect Aβ scavengers rhythmicity and that Aβ clearance is a rhythmic process possibly regulated by the rhythmic expression of Aβ scavengers.
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