Helper T-cell heterogeneity: a complex developmental issue in the immune system

T cell infiltration mediates neurodegeneration and cognitive decline in Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder with pathological features of β-amyloid (Aβ) and hyperphosphorylated tau protein accumulation in the brain, often accompanied by cognitive decline. So far, our understanding of the extent and role of adaptive immune responses in AD has been quite limited. T cells, as essential members of the adaptive immune system, exhibit quantitative and functional abnormalities in the brains of AD patients. Dysfunction of the blood-brain barrier (BBB) in AD is considered one of the factors leading to T cell infiltration. Moreover, the degree of neuronal loss in AD is correlated with the quantity of T cells. We first describe the differentiation and subset functions of peripheral T cells in AD patients and provide an overview of the key findings related to BBB dysfunction and how T cells infiltrate the brain parenchyma through the BBB. Furthermore, we emphasize the risk factors associated with AD, including Aβ, Tau protein, microglial cells, apolipoprotein E (ApoE), and neuroinflammation. We discuss their regulation of T cell activation and proliferation, as well as the connection between T cells, neurodegeneration, and cognitive decline. Understanding the innate immune response is crucial for providing comprehensive personalized therapeutic strategies for AD.

Activated T Lymphocytes are Essential Drivers of Pathological Remodeling in Ischemic Heart Failure

BACKGROUND

Inappropriately sustained inflammation is a hallmark of chronic ischemic heart failure (HF); however, the pathophysiological role of T lymphocytes is unclear.

METHODS AND RESULTS

Permanent coronary ligation was performed in adult C57BL/6 mice. When compared with sham-operated mice, mice with HF (8 weeks after ligation) exhibited the following features: (1) significant (P<0.05) expansion of circulating CD3⁺CD8⁺ cytotoxic and CD3⁺CD4⁺ helper (Th) T lymphocytes, together with increased Th1, Th2, Th17, and regulatory T-cell (Treg) CD4⁺ subsets; (2) significant expansion of CD8⁺ and CD4⁺ T cells in failing myocardium, with increased Th1, Th2, Th17, and Treg CD4⁺ subsets, marked reduction of the Th1/Th2 ratio, augmentation of the Th17/Treg ratio, and upregulation of Th2 cytokines; and (3) significantly increased Th1, Th2, Th17 cells, and Tregs, in the spleen and mediastinal lymph nodes, with expansion of splenic antigen-experienced effector and memory CD4⁺ T cells. Antibody-mediated CD4⁺ T-cell depletion in HF mice (starting 4 weeks after ligation) reduced cardiac infiltration of CD4⁺ T cells and prevented progressive left ventricular dilatation and hypertrophy, whereas adoptive transfer of splenic CD4⁺ T cells (and, to a lesser extent, cardiac CD3⁺ T cells) from donor mice with HF induced long-term left ventricular dysfunction, fibrosis, and hypertrophy in naive recipient mice.

CONCLUSIONS

CD4⁺ T lymphocytes are globally expanded and activated in chronic ischemic HF, with Th2 (versus Th1) and Th17 (versus Treg) predominance in failing hearts, and with expansion of memory T cells in the spleen. Cardiac and splenic T cells in HF are primed to induce cardiac injury and remodeling, and retain this memory on adoptive transfer.

Lymph Node Stroma Dynamics and Approaches for Their Visualization

Lymphoid stromal cells are best known as the architectural cells of lymphoid organs. For decades, they have been considered as inert elements of the immune system but this view has changed dramatically in recent years, when it was discovered that they are endowed with critical immunoregulatory functions. It is now accepted that without them, the adaptive immune response would be compromised, if not abrogated entirely. Here, we review the function of the major lymphoid stromal cell types; the way they remodel upon inflammation; discuss the available tools to track their behavior; and introduce several methodological approaches that we believe will help improving our knowledge of these pivotal cell types.

CD4+ T Cells Mediate Aspergillosis Vaccine Protection

Adaptive effector CD4⁺ T cells play essential roles in the defense against fungal infections, especially against invasive aspergillosis (IA). Such protective CD4⁺ T cells can be generated through immunization with specialized antifungal vaccines, as has been demonstrated for pulmonary Aspergillus fumigatus infections in mouse experiments. Adaptive transfer of fungal antigen-specific CD4⁺ T cells conferred protection onto non-immunized naive mice, an experimental approach that could potentially become a future treatment option for immunosuppressed IA patients, focusing on the ultimate goal to improve their otherwise dim chances for survival. Here, we describe the different techniques to analyze CD4⁺ T cell immune responses after immunization with a recombinant fungal protein. We present three major methods that are used to analyze the role of CD4⁺ T cells in protection against A. fumigatus challenge. They include (1) transplantation of CD4⁺ T cells from vaccinated mice into immunosuppressed naive mice, observing increasing protection of the cell recipients, (2) depletion of CD4⁺ T cells from vaccinated mice, which abolishes vaccine protection, and (3) T cell proliferation studies following stimulation with overlapping synthetic peptides or an intact protein vaccine. The latter can be used to validate immunization status and to identify protective T cell epitopes in vaccine antigens. In the methods detailed here, we used versions of the well-studied Asp f3 protein expressed in a bacterial host, either as the intact full length protein or its N-terminally truncated version, comprised of residues 15-168. However, these methods are generally applicable and can well be adapted to study other protein-based subunit vaccines.

Gene Expression Profiling in Blood and Affected Muscle Tissues Reveals Differential Activation Pathways in Patients with New-onset Juvenile and Adult Dermatomyositis

OBJECTIVE

To identify shared and differential molecular pathways in blood and affected muscle between adult dermatomyositis (DM) and juvenile DM, and their association with clinical disease activity measures.

METHODS

Gene expression of transcription factors and cytokines involved in differentiation and effector function of T cell subsets, regulatory T cells and follicular Th cells, were analyzed in the blood from 21 newly diagnosed adult and 26 juvenile DM subjects and in 15 muscle specimens (7 adult and 8 juvenile DM) using a custom RT2 Profiler PCR Array. Disease activity was determined and measured by established disease activity tools.

RESULTS

The most prominent finding was the higher blood expression of Th17-related cytokines [retinoic acid-related orphan receptor-γ, interferon regulatory factor 4, interleukin (IL)-23A, IL-6, IL-17F, and IL-21] in juvenile DM at baseline. In contrast, adult patients with DM showed increased blood levels of STAT3 and BCL6 compared with juvenile DM. In muscle, GATA3, IL-13, and STAT5B were found at higher levels in juvenile patients with DM compared with adult DM. Among 25 patients (11 adult and 14 juvenile DM) who had blood samples at baseline and at 6 months, increased expression of IL-1β, STAT3, STAT6, STAT5B, and BCL6 was associated with an improvement in global extramuscular disease activity.

CONCLUSION

We observed differences in gene expression profiling in blood and muscle between new-onset adult and juvenile DM. Cytokine expression in the blood of juvenile patients with new-onset DM was dominated by Th17-related cytokines compared with adult patients with DM. This may reflect the activation of different Th pathways between muscle and blood.

Intervention of PKC-θ as an immunosuppressive regimen

PKC-θ is selectively enriched in T cells and specifically translocates to immunological synapse where it mediates critical T cell receptor signals required for T cell activation, differentiation, and survival. T cells deficient in PKC-θ are defective in their ability to differentiate into inflammatory effector cells that mediate actual immune responses whereas, their differentiation into regulatory T cells (Treg) that inhibits the inflammatory T cells is enhanced. Therefore, the manipulation of PKC-θ activity can shift the ratio between inflammatory effector T cells and inhibitory Tregs, to control T cell-mediated immune responses that are responsible for autoimmunity and allograft rejection. Indeed, PKC-θ-deficient mice are resistant to the development of several Th2 and Th17-dependent autoimmune diseases and are defective in mounting alloimmune responses required for rejection of transplanted allografts and graft-versus-host disease. Selective inhibition of PKC-θ is therefore considered as a potential treatment for prevention of autoimmune diseases and allograft rejection.

β-catenin/TCF-1 pathway in T cell development and differentiation

T cells must undergo two critical differentiation processes before they become competent effectors that can mediate actual immune responses. Progenitor T cells undergo defined stages of differentiation in the thymus, which include positive and negative selection, to generate a repertoire of T cells that will respond to foreign but not self antigens. When these immunocompetent T cells first migrate out of thymus into peripheral lymphoid tissues, they are naïve and are unable to mediate immune responses. However, upon antigen encounter, peripheral CD4+ naïve T cells undergo another differentiation process to become armed effector T cells including Th1, Th2, Th17 or regulatory T cells, all of which are capable of regulating immune responses. A canonical Wnt/β-catenin/T cell factor (TCF) pathway has been shown to regulate T cell differentiation in both the thymus and in peripheral lymphoid tissues. Dysfunction of this pathway at any stage of T cell differentiation could lead to severe autoimmunity including experimental autoimmune encephalomyelitis or immune deficiency. Understanding the role played by β-catenin/TCF-1 in T cell differentiation will facilitate our understanding of the mechanisms that regulate T cell function and assist in identifying novel therapy targets for treating both autoimmune and immune diseases. Therefore, in this review, we will focus on the function of β-catenin/TCF-1 pathway in the regulation of thymic and peripheral T cell differentiation processes.