T cell immune response within B-cell follicles

Coordinated expansion of memory T follicular helper and B cells mediates spontaneous clearance of HCV reinfection

Introduction

Follicular helper T cells are essential for helping in the maturation of B cells and the production of neutralizing antibodies (NAbs) during primary viral infections. However, their role during recall responses is unclear. Here, we used hepatitis C virus (HCV) reinfection in humans as a model to study the recall collaborative interaction between circulating CD4 T follicular helper cells (cTfh) and memory B cells (MBCs) leading to the generation of NAbs.

Methods

We evaluated this interaction longitudinally in subjects who have spontaneously resolved primary HCV infection during a subsequent reinfection episode that resulted in either another spontaneous resolution (SR/SR, n = 14) or chronic infection (SR/CI, n = 8).

Results

Both groups exhibited virus-specific memory T cells that expanded upon reinfection. However, early expansion of activated cTfh (CD4+CXCR5+PD-1+ICOS+FoxP3-) occurred in SR/SR only. The frequency of activated cTfh negatively correlated with time post-infection. Concomitantly, NAbs and HCV-specific MBCs (CD19+CD27+IgM-E2-Tet+) peaked during the early acute phase in SR/SR but not in SR/CI. Finally, the frequency of the activated cTfh1 (CXCR3+CCR6-) subset correlated with the neutralization breadth and potency of NAbs.

Conclusion

These results underscore a key role for early activation of cTfh1 cells in helping antigen-specific B cells to produce NAbs that mediate the clearance of HCV reinfection.

CD4+ T-cell subsets in autoimmune hepatitis: A review

Autoimmune hepatitis (AIH) is a chronic autoimmune liver disease that can lead to hepatocyte destruction, inflammation, liver fibrosis, cirrhosis, and liver failure. The diagnosis of AIH requires the identification of lymphoblast cell interface hepatitis and serum biochemical abnormalities, as well as the exclusion of related diseases. According to different specific autoantibodies, AIH can be divided into AIH-1 and AIH-2. The first-line treatment for AIH is a corticosteroid and azathioprine regimen, and patients with liver failure require liver transplantation. However, the long-term use of corticosteroids has obvious side effects, and patients are prone to relapse after drug withdrawal. Autoimmune diseases are characterized by an imbalance in immune tolerance of self-antigens, activation of autoreactive T cells, overactivity of B cells, and increased production of autoantibodies. CD4+ T cells are key players in adaptive immunity and can secrete cytokines, activate B cells to produce antibodies, and influence the cytotoxicity of CD8+ T cells. According to their characteristics, CD4+ T cells can be divided into different subsets. In this review, we discuss the changes in T helper (Th)1, Th2, Th17, Th9, Th22, regulatory T cell, T follicular helper, and T peripheral helper cells and their related factors in AIH and discuss the therapeutic potential of targeting CD4+ T-cell subsets in AIH.

Delayed generation of functional virus-specific circulating T follicular helper cells correlates with severe COVID-19

Effective humoral immune responses require well-orchestrated B and T follicular helper (Tfh) cell interactions. Whether these interactions are impaired and associated with COVID-19 disease severity is unclear. Here, longitudinal blood samples across COVID-19 disease severity are analysed. We find that during acute infection SARS-CoV-2-specific circulating Tfh (cTfh) cells expand with disease severity. SARS-CoV-2-specific cTfh cell frequencies correlate with plasmablast frequencies and SARS-CoV-2 antibody titers, avidity and neutralization. Furthermore, cTfh cells but not other memory CD4 T cells, from severe patients better induce plasmablast differentiation and antibody production compared to cTfh cells from mild patients. However, virus-specific cTfh cell development is delayed in patients that display or later develop severe disease compared to those with mild disease, which correlates with delayed induction of high-avidity neutralizing antibodies. Our study suggests that impaired generation of functional virus-specific cTfh cells delays high-quality antibody production at an early stage, potentially enabling progression to severe disease.

Phenotypes of peripheral CD4+ T helper cell subsets in pregnant women with HBeAg-negative chronic asymptomatic HBV carriers

Background

Chronic hepatitis B virus (HBV) infection is a major public health problem worldwide, and mother-to-child transmission is the key mode of HBV infection. CD4⁺ T helper (Th) cells play a critical role in the immune microenvironment of specific maternal tolerance to the foetus during pregnancy. However, the roles of Th cell subsets in pregnant women (PW) with chronic asymptomatic HBV carriers (ASCs) remain completely unclear. Here, we aimed to characterize CD4⁺ T-cell immunity in PW with hepatitis Be antigen (HBeAg)-negative chronic ASCs.

Methods

Human peripheral blood mononuclear cells (PBMCs) from PW without HBV infection or with chronic ASCs and healthy controls (HC) were isolated, and CD4⁺ Th cell subsets were detected by flow cytometry in addition to serum cytokines. Serological HBV markers, liver function and hormone levels of these individuals were also tested.

Results

The frequencies of circulating T follicular helper (Tfh) type 2 (Tfh2) cells were significantly evaluated, but Tfh1 cell frequencies were notably decreased in PW compared to HC. Moreover, the frequencies of Th22 cells were only notably increased in PW with chronic ASCs in comparison with PW. Additionally, increased levels of serum IL-4 were positively correlated with Tfh2 cell frequencies in healthy PW. Interestingly, serum P4 levels were positively associated with the frequencies of circulating Tfh2 or Th2 cells but were negatively related to the frequencies of circulating Tfh17 or Th17 cells in healthy PW. Although there were some changes in the other CD4⁺ Th cell frequencies and cytokine levels or other references, significant differences were not found among HC, healthy PW, PW with HBeAg-negative chronic ASCs.

Conclusion

CD4⁺ Th cell subsets played a critical role in the immune microenvironment of PW, and these findings provided potential evidence for why PW with chronic ASCs did not receive antenatal antiviral prophylaxis.

Inhaled particulate accumulation with age impairs immune function and architecture in human lung lymph nodes

Older people are particularly susceptible to infectious and neoplastic diseases of the lung and it is unclear how lifelong exposure to environmental pollutants affects respiratory immune function. In an analysis of human lymph nodes (LNs) from 84 organ donors aged 11-93 years, we found a specific age-related decline in lung-associated, but not gut-associated, LN immune function linked to the accumulation of inhaled atmospheric particulate matter. Increasing densities of particulates were found in lung-associated LNs with age, but not in the corresponding gut-associated LNs. Particulates were specifically contained within CD68⁺CD169^- macrophages, which exhibited decreased activation, phagocytic capacity, and altered cytokine production compared with non-particulate-containing macrophages. The structures of B cell follicles and lymphatic drainage were also disrupted in lung-associated LNs with particulates. Our results reveal that the cumulative effects of environmental exposure and age may compromise immune surveillance of the lung via direct effects on immune cell function and lymphoid architecture.

Follicular Helper T Cells in the Immunopathogenesis of SARS-CoV-2 Infection

Coronavirus disease 2019 (COVID-19), caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a serious infectious disease that has led to a global pandemic with high morbidity and mortality. High-affinity neutralizing antibody is important for controlling infection, which is closely regulated by follicular helper T (Tfh) cells. Tfh cells play a central role in promoting germinal center reactions and driving cognate B cell differentiation for antibody secretion. Available studies indicate a close relationship between virus-specific Tfh cell-mediated immunity and SARS-CoV-2 infection progression. Although several lines of evidence have suggested that Tfh cells contribute to the control of SARS-CoV-2 infection by eliciting neutralizing antibody productions, further studies are needed to elucidate Tfh-mediated effector mechanisms in anti-SARS-CoV-2 immunity. Here, we summarize the functional features and roles of virus-specific Tfh cells in the immunopathogenesis of SARS-CoV-2 infection and in COVID-19 vaccines, and highlight the potential of targeting Tfh cells as therapeutic strategy against SARS-CoV-2 infection.

High-frequency and activation of CD4+CD25+ T cells maintain persistent immunotolerance induced by congenital ALV-J infection

Congenital avian leukosis virus subgroup J (ALV-J) infection can induce persistent immunotolerance in chicken, however, the underlying mechanism remains unclear. Here, we demonstrate that congenital ALV-J infection induces the production of high-frequency and activated CD4⁺CD25⁺ Tregs that maintain persistent immunotolerance. A model of congenital infection by ALV-J was established in fertilized eggs, and hatched chicks showed persistent immunotolerance characterized by persistent viremia, immune organ dysplasia, severe imbalance of the ratio of CD4⁺/CD8⁺ T cells in blood and immune organs, and significant decrease in CD3⁺ T cells and Bu-1⁺ B cells in the spleen. Concurrently, the mRNA levels of IL-2, IL-10, and IFN-γ showed significant fluctuations in immune organs. Moreover, the frequency of CD4⁺CD25⁺ Tregs in blood and immune organs significantly increased, and the frequency of CD4⁺CD25⁺ Tregs was positively correlated with changes in ALV-J load in immune organs. Interestingly, CD4⁺CD25⁺ Tregs increased in the marginal zone of splenic nodules in ALV-J-infected chickens and dispersed to the germinal center. In addition, the proliferation and activation of B cells in splenic nodules was inhibited, and the number of IgM⁺ and IgG⁺ cells in the marginal zone significantly decreased. We further found that the mRNA levels of TGF- β and CTLA-4 in CD4⁺CD25⁺ Tregs of ALV-J-infected chickens significantly increased. Together, high-frequency and activated CD4⁺CD25⁺ Tregs inhibited B cells functions by expressing the inhibitory cytokine TGF-β and inhibitory surface receptor CTLA-4, thereby maintaining persistent immunotolerance in congenital ALV-J-infected chickens.

ACLY ubiquitination by CUL3-KLHL25 induces the reprogramming of fatty acid metabolism to facilitate iTreg differentiation

Inducible regulatory T (iTreg) cells play a central role in immune suppression. As iTreg cells are differentiated from activated T (Th0) cells, cell metabolism undergoes dramatic changes, including a shift from fatty acid synthesis (FAS) to fatty acid oxidation (FAO). Although the reprogramming in fatty acid metabolism is critical, the mechanism regulating this process during iTreg differentiation is still unclear. Here we have revealed that the enzymatic activity of ATP-citrate lyase (ACLY) declined significantly during iTreg differentiation upon transforming growth factor β1 (TGFβ1) stimulation. This reduction was due to CUL3-KLHL25-mediated ACLY ubiquitination and degradation. As a consequence, malonyl-CoA, a metabolic intermediate in FAS that is capable of inhibiting the rate-limiting enzyme in FAO, carnitine palmitoyltransferase 1 (CPT1), was decreased. Therefore, ACLY ubiquitination and degradation facilitate FAO and thereby iTreg differentiation. Together, we suggest TGFβ1-CUL3-KLHL25-ACLY axis as an important means regulating iTreg differentiation and bring insights into the maintenance of immune homeostasis for the prevention of immune diseases.

Follicular regulatory T cell biology and its role in immune-mediated diseases

Follicular regulatory T (Tfr) cells are recently found to be a special subgroup of regulatory T (Treg) cells. Tfr cells play an important role in regulating the germinal center (GC) response, especially modulating follicular helper T (Tfh) cells and GC-B cells, thereby affecting the production of antibodies. Tfr cells are involved in the generation and development of many immune-related and inflammatory diseases. This article summarizes the advances in several aspects of Tfr cell biology, with special focus on definition and phenotype, development and differentiation, regulatory factors, functions, and interactions with T/B cells and molecules involved in performance and regulation of Tfr function. Finally, we highlight the current understanding of Tfr cells involvement in autoimmunity and alloreactivity, and describe some drugs targeting Tfr cells. These latest studies have answered some basic questions in Tfr cell biology and explored the roles of Tfr cells in immune-mediated diseases.

The dichotomous and incomplete adaptive immunity in COVID-19 patients with different disease severity

The adaptive immunity that protects patients from coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is not well characterized. In particular, the asymptomatic patients have been found to induce weak and transient SARS-CoV-2 antibody responses, but the underlying mechanisms remain unknown; meanwhile, the protective immunity that guide the recovery of these asymptomatic patients is elusive. Here, we characterized SARS-CoV-2-specific B-cell and T-cell responses in 10 asymptomatic patients and 64 patients with other disease severity (mild, n = 10, moderate, n = 32, severe, n = 12) and found that asymptomatic or mild symptomatic patients failed to mount virus-specific germinal center (GC) B cell responses that result in robust and prolonged humoral immunity, assessed by GC response indicators including follicular helper T (TFH) cell and memory B cell responses as well as serum CXCL13 levels. Alternatively, these patients mounted potent virus-specific TH1 and CD8+ T cell responses. In sharp contrast, patients of moderate or severe disease induced vigorous virus-specific GC B cell responses and associated TFH responses; however, the virus-specific TH1 and CD8+ T cells were minimally induced in these patients. These results, therefore, uncovered the protective immunity in asymptomatic patients and also revealed the strikingly dichotomous and incomplete humoral and cellular immune responses in COVID-19 patients with different disease severity, providing important insights into rational design of effective COVID-19 vaccines.

The direct and indirect regulation of follicular T helper cell differentiation in inflammation and cancer

Follicular T helper (Tfh) cells play important roles in facilitating B-cell differentiation and inducing the antibody response in humoral immunity and immune-associated inflammatory diseases, including infections, autoimmune diseases, and cancers. However, Tfh cell differentiation is mainly achieved through self-directed differentiation regulation and the indirect regulation mechanism of antigen-presenting cells (APCs). During the direct intrinsic differentiation of naïve CD4⁺ T cells into Tfh cells, Bcl-6, as the characteristic transcription factor, plays the core role of transcriptional regulation. APCs indirectly drive Tfh cell differentiation mainly by changing cytokine secretion mechanisms. Altered metabolic signaling is also critically involved in Tfh cell differentiation. This review summarizes the recent progress in understanding the direct and indirect regulatory signals and metabolic mechanisms of Tfh cell differentiation and function in immune-associated diseases.

Bcl6 Preserves the Suppressive Function of Regulatory T Cells During Tumorigenesis

During tumorigenesis, tumor infiltrating regulatory T (Treg) cells restrict the function of effector T cells in tumor microenvironment and thereby promoting tumor growth. The anti-tumor activity of effector T cells can be therapeutically unleashed, and is now being exploited for the treatment of various types of human cancers. However, the immune suppressive function of Treg cells remains a major hurdle to broader effectiveness of tumor immunotherapy. In this article, we reported that the deletion of Bcl6 specifically in Treg cells led to stunted tumor growth, which was caused by impaired Treg cell responses. Notably, Bcl6 is essential in maintaining the lineage stability of Treg cells in tumor microenvironment. Meanwhile, we found that the absence of follicular regulatory T (Tfr) cells, which is a result of Bcl6 deletion in Foxp3+ cells, was dispensable for tumor control. Importantly, the increased Bcl6 expression in Treg cells is associated with poor prognosis of human colorectal cancer and lymph node metastasis of skin melanoma. Furthermore, Bcl6 deletion in Treg cells exhibits synergistic effects with immune checkpoint blockade therapy. Collectively, these results indicate that Bcl6 actively participates in regulating Treg cell immune responses during tumorigenesis and can be exploited as a therapeutic target of anti-tumor immunity.