New insights into the differentiation and function of T follicular helper cells

Activated Circulating T Follicular Helper Cells Are Associated with Disease Severity in Patients with Psoriasis

Circulating T follicular helper (cTfh) cells are known to be involved in numerous immune-mediated diseases, but their pathological role in psoriasis is less fully investigated. Herein, we aimed to identify whether cTfh cells contributed to the pathogenesis of psoriasis. The frequency and function of cTfh cells were compared between patients with psoriasis vulgaris and healthy controls, and the infiltration of Tfh cells was detected between lesional and nonlesional skin tissues of psoriasis patients. Moreover, the dynamic change of cTfh cells before and after acitretin treatment was evaluated. Our results showed both increased frequency and activation (indicated by higher expression of ICOS, PD-1, HLA-DR, and Ki-67 and increased production of IL-21, IL-17, and IFN-γ) of cTfh cells in psoriasis patients. Compared with nonlesional skin tissues of psoriasis patients, the number of infiltrated Tfh cells was significantly increased in psoriasis lesions. In addition, positive correlations between the percentage of cTfh, functional markers on cTfh cells in peripheral blood and disease severity were noted. Furthermore, the frequency of cTfh cells and the levels of cytokines secreted by cTfh cells were all significantly decreased after 1-month treatment.

Early changes within the lymphocyte population are associated with the development of multiple organ dysfunction syndrome in trauma patients

BACKGROUND

Early survival following severe injury has been improved with refined resuscitation strategies. Multiple organ dysfunction syndrome (MODS) is common among this fragile group of patients leading to prolonged hospital stay and late mortality. MODS after trauma is widely attributed to dysregulated inflammation but the precise mechanics of this response and its influence on organ injury are incompletely understood. This study was conducted to investigate the relationship between early lymphocyte responses and the development of MODS during admission.

METHODS

During a 24-month period, trauma patients were recruited from an urban major trauma centre to an ongoing, observational cohort study. Admission blood samples were obtained within 2 h of injury and before in-hospital intervention, including blood transfusion. The study population was predominantly male with a blunt mechanism of injury. Lymphocyte subset populations including T helper, cytotoxic T cells, NK cells and γδ T cells were identified using flow cytometry. Early cytokine release and lymphocyte count during the first 7 days of admission were also examined.

RESULTS

This study demonstrated that trauma patients who developed MODS had an increased population of NK dim cells (MODS vs no MODS: 22 % vs 13 %, p < 0.01) and reduced γδ-low T cells (MODS vs no MODS: 0.02 (0.01-0.03) vs 0.09 (0.06-0.12) × 10^9/L, p < 0.01) at admission. Critically injured patients who developed MODS (n = 27) had higher interferon gamma (IFN-γ) concentrations at admission, compared with patients of matched injury severity and shock (n = 60) who did not develop MODS (MODS vs no MODS: 4.1 (1.8-9.0) vs 1.0 (0.6-1.8) pg/ml, p = 0.01). Lymphopenia was observed within 24 h of injury and was persistent in those who developed MODS. Patients with a lymphocyte count of 0.5 × 10(9)/L or less at 48 h, had a 45 % mortality rate.

CONCLUSIONS

This study provides evidence of lymphocyte activation within 2 h of injury, as demonstrated by increased NK dim cells, reduced γδ-low T lymphocytes and high blood IFN-γ concentration. These changes are associated with the development of MODS and lymphopenia. The study reveals new opportunities for investigation to characterise the cellular response to trauma and examine its influence on recovery.

A critical role of T follicular helper cells in human mucosal anti-influenza response that can be enhanced by immunological adjuvant CpG-DNA

T Follicular helper cells (TFH) are considered critical for B cell antibody response, and recent efforts have focused on promoting TFH in order to enhance vaccine efficacy. We studied the frequency and function of TFH in nasopharynx-associated lymphoid tissues (NALT) from children and adults, and its role in anti-influenza antibody response following stimulation by a live-attenuated influenza vaccine (LAIV) or an inactivated seasonal virus antigen (sH1N1). We further studied whether CpG-DNA promotes TFH and by which enhances anti-influenza response. We showed NALT from children aged 1.5-10 years contained abundant TFH, suggesting efficient priming of TFH during early childhood. Stimulation by LAIV induced a marked increase in TFH that correlated with a strong production of anti-hemagglutinin (HA) IgA/IgG/IgM antibodies in tonsillar cells. Stimulation by the inactivated sH1N1 antigen induced a small increase in TFH which was markedly enhanced by CpG-DNA, accompanied by enhanced anti-HA antibody responses. In B cell co-culture experiment, anti-HA responses were only seen in the presence of TFH, and addition of plasmacytoid dendritic cell to TFH-B cell co-culture enhanced the TFH-mediated antibody production following CpG-DNA and sH1N1 antigen stimulation. Induction of TFH differentiation from naïve T cells was also shown following the stimulation. Our results support a critical role of TFH in human mucosal anti-influenza antibody response. Use of an adjuvant such as CpG-DNA that has the capacity to promote TFH by which to enhance antigen-induced antibody responses in NALT tissue may have important implications for future vaccination strategies against respiratory pathogens.

Follicular helper T cells mediate IgE antibody response to airborne allergens

BACKGROUND

T_H2 cells have long been believed to play a pivotal role in allergic immune responses, including IgE antibody production and type 2 cytokine-mediated inflammation and pathology. A new T-cell subset, follicular helper T (T_FH) cells, is specialized in supporting B-cell maturation and antibody production.

OBJECTIVE

We sought to investigate the roles of T_FH cells in allergic immune responses.

METHODS

Naive mice were exposed to cytokines or natural allergens through the airways. Development of allergic immune responses was analyzed by collecting draining lymph nodes and sera and by challenging the animals. Cytokine reporter mice and gene-deficient mice were used to dissect the immunologic mechanisms.

RESULTS

We observed the development of IL-4-producing T_FH cells and T_H2 cells in draining lymph nodes after airway exposure to IL-1 family cytokines or natural allergens. T_FH and T_H2 cells demonstrated unique phenotypes, tissue localization, and cytokine responses. T_FH cells supported the sustained production of IgE antibody in vivo in the absence of other T-cell subsets or even when T_H2 cell functions were severely compromised. Conversely, conditional deficiency of the master regulator Bcl6 in CD4⁺ T cells resulted in a marked reduction in T_FH cell numbers and IgE antibody levels, but type 2 cytokine responses and eosinophilic inflammation in the airways remained unaffected.

CONCLUSION

T_FH cells play critical roles in the regulation of IgE antibody production. Allergic immune responses to airborne allergens likely involve 2 distinct subsets of IL-4-producing CD4⁺ T cells, namely T_FH and Th2 cells.

Follicular helper T cell in immunity and autoimmunity

The traditional concept that effector T helper (Th) responses are mediated by Th1/Th2 cell subtypes has been broadened by the recent demonstration of two new effector T helper cells, the IL-17 producing cells (Th17) and the follicular helper T cells (Tfh). These new subsets have many features in common, such as the ability to produce IL-21 and to express the IL-23 receptor (IL23R), the inducible co-stimulatory molecule ICOS, and the transcription factor c-Maf, all of them essential for expansion and establishment of the final pool of both subsets. Tfh cells differ from Th17 by their ability to home to B cell areas in secondary lymphoid tissue through interactions mediated by the chemokine receptor CXCR5 and its ligand CXCL13. These CXCR5+ CD4+ T cells are considered an effector T cell type specialized in B cell help, with a transcriptional profile distinct from Th1 and Th2 cells. The role of Tfh cells and its primary product, IL-21, on B-cell activation and differentiation is essential for humoral immunity against infectious agents. However, when deregulated, Tfh cells could represent an important mechanism contributing to exacerbated humoral response and autoantibody production in autoimmune diseases. This review highlights the importance of Tfh cells by focusing on their biology and differentiation processes in the context of normal immune response to infectious microorganisms and their role in the pathogenesis of autoimmune diseases.

T helper 2 and T follicular helper cells: Regulation and function of interleukin-4

Type 2 immunity is characterized by expression of the cytokines interleukin (IL)-4, IL-5, IL-9 and IL-13, which can function in mediating protective immunity in the host or possess a pathogenic role. T helper (Th) 2 cells have emerged to play a beneficial role in mediating anti-parasitic immunity and are also known to be key players in mediating allergic diseases. In addition to the Th2 cells, recent studies have identified T follicular helper (Tfh) cells as an alternative source of IL-4 to regulate type 2 humoral immune responses, indicating that Th2 and Tfh cells exhibit overlapping phenotypical and functional characteristics. Th2 and Tfh cells appear to utilize distinct mechanisms for regulation of IL-4 expression; however unlike Th2 cells, the regulation and function of Tfh-derived IL-4 is not yet fully understood. Understanding of the molecular mechanisms for IL-4 expression and function in both cell subsets will be beneficial for the development of future therapeutic interventions.

Spleen and Liver

In liver cirrhosis, the spleen is a source of nitric oxide which affects a hyperdynamic state typical of portal hypertension. It is generally accepted that pancytopenia results predominantly from the increased phagocytosis and destruction of hemocytes in splenic macrophages. In addition, liver fibrosis is amplified by migrated Th2 lymphocytes and transforming growth factor beta from the spleen. There is a possibility that increase of the spleen stiffness is the primary factor of idiopathic portal hypertension. Spleen stiffness is caused by bleeding, fibrosis, and calcareous deposits after increase in red pulp pressure due to venous congestion. In nonalcoholic steatohepatitis, macrophage activity in the spleen is upregulated. In addition, high levels of inflammatory cytokines are produced and T cell shows increased proliferation in the spleen. In autoimmune hepatitis model, CD4⁺ T cells are differentiated into follicular helper T cells (T_FH) in the spleen. T_FH cells promoted hypergammaglobulinemia and antinuclear antibodies production. T_FH cells migrate from the spleen to the liver, triggering induction of autoimmune hepatitis in this model. IgM-positive B cells localize in the CD21-positive lymph follicle in the spleen of primary biliary cholangitis. These findings prove that the spleen influences on the pathogenesis and severity of several kinds of liver disease.

Limited Internodal Migration of T Follicular Helper Cells after Peripheral Infection with Herpes Simplex Virus-1

The ability of CD4 T cells to give rise to specialized T follicular helper cells (TFH) critical to initiating appropriate Ab responses is regulated by environmental cues in lymphoid tissues draining the site of infection. In this study, we used a skin infection with HSV-1 characterized by the successive involvement of interconnected but distinct lymph nodes (LNs), to investigate the anatomical diversification of virus-specific CD4 T cell responses and the migratory capacity of TFH or their precursors. Whereas Th1 effector CD4 T cells expressing peripheral-targeting migration molecules readily migrated from primary to secondary reactive LNs, Bcl6(+) CXCR5(+) PD1(hi) TFH were largely retained at the site of initial activation with little spillover into the downstream LNs involved at later stages of infection. Consistent with this, TFH maintained high-level surface expression of CD69, indicative of impaired migratory capacity. Notably, the biased generation and retention of TFH in primary LNs correlated with a preferential generation of germinal centers at this site. Our results highlight a limited anatomical diversification of TFH responses and germinal center reactions that were imprinted within the first few cell divisions during TFH differentiation in LNs draining the site of initial infection.

Higher Frequency of CD4+CXCR5+ICOS+PD1+ T Follicular Helper Cells in Patients With Infectious Mononucleosis

Follicular helper T (Tfh) cells are recognized as a distinct CD4helper T cell subset, and mainly dysregulated in the autoimmune disease, whether it plays a role in the infectious mononucleosis (IM) diseases is unknown. In this study, we found that the CD4CXCR5 Tfh cells were not significantly changed, but the CD4CXCR5ICOS and CD4CXCR5ICOSPD1 Tfh subsets were significantly increased in the IM patients, and all these cells were significantly changed after antiviral therapy. Second, only the numbers of CD4CXCR5ICOSPD1 Tfh cells correlated with the Epstein-Barr virus (EBV) DNA load, negatively correlated with the numbers of naive B cells and amount of IL-21, and positively correlated with the numbers of plasma cells, memory B cells, and atypical lymphocytes. Third, the frequency of CD4CXCR5ICOSPD1 Tfh subset was significantly higher in lymphadenectasis or hepatosplenomegaly patients, and associated with the level of alanine aminotransferase (ALT). All together, our findings discovered this CD4CXCR5ICOSPD1 Tfh cell subset might play an important role in the pathogenesis of IM.

Functional and Phenotypic Plasticity of CD4(+) T Cell Subsets

The remarkable plasticity of CD4(+) T cells allows individuals to respond to environmental stimuli in a context-dependent manner. A balance of CD4(+) T cell subsets is critical to mount responses against pathogen challenges to prevent inappropriate activation, to maintain tolerance, and to participate in antitumor immune responses. Specification of subsets is a process beginning in intrathymic development and continuing within the circulation. It is highly flexible to adapt to differences in nutrient availability and the tissue microenvironment. CD4(+) T cell subsets have significant cross talk, with the ability to "dedifferentiate" given appropriate environmental signals. This ability is dependent on the metabolic status of the cell, with mTOR acting as the rheostat. Autoimmune and antitumor immune responses are regulated by the balance between regulatory T cells and Th17 cells. When a homeostatic balance of subsets is not maintained, immunopathology can result. CD4(+) T cells carry complex roles within tumor microenvironments, with context-dependent immune responses influenced by oncogenic drivers and the presence of inflammation. Here, we examine the signals involved in CD4(+) T cell specification towards each subset, interconnectedness of cytokine networks, impact of mTOR signaling, and cellular metabolism in lineage specification and provide a supplement describing techniques to study these processes.

Dysregulated development of IL-17- and IL-21-expressing follicular helper T cells and increased germinal center formation in the absence of RORγt

Interleukin 17-producing helper T (Th17) cells have been widely defined by the lineage transcription factor retinoid-related orphan receptor (ROR)γt. Pathophysiologically, these cells play a crucial role in autoimmune diseases and have been linked to dysregulated germinal center (GC) reactions and autoantibody production. In this study, we used gene expression and flow cytometric analyses for the characterization of Rorγt(-/-) and Rorγt(-/-)Il21(RFP/+) mice to demonstrate a previously unknown transcriptional flexibility in the development of IL-17-producing Th-cell subsets. We found an accumulation of follicular Th (Tfh) cells by 5.2-fold, spontaneous 13-fold higher GC formation, decreased frequency of follicular Foxp3(+) T-regulatory (Treg) cells (50%), and a 3.4-fold increase in the number of proliferating follicular B cells in RORγt-deficient vs. wild-type mice. Dysregulated B-cell responses were associated with enhanced production of IL-17 (6.4-fold), IL-21 (2.2-fold), and B-cell-activating factor (BAFF) (2-fold) and were partially rescued by adoptive transfer of Treg cells. In an unexpected finding, we detected RORγt-independent IL-17 expression in ICOS(+)CXCR5(+)Tfh and in ICOS(+)CXCR5(-)Th cells. Based on the observed high Irf4 and Batf gene expression, we suggest that CD4(+) T-cell transcription factors other than RORγt can cooperatively induce differentiation of IL-17-producing Th cells, including Th17-like Tfh-cell subsets. We conclude that the occurrence of aberrant Tfh and follicular Treg cells support spontaneous GC formation and dysregulated B-cell responses in RORγt-deficient mice.

Avian pathogenic Escherichia coli (APEC) infection alters bone marrow transcriptome in chickens

Background

Avian pathogenic Escherichia coli (APEC) is a major cause of disease impacting animal health. The bone marrow is the reservoir of immature immune cells; however, it has not been examined to date for gene expression related to developmental changes (cell differentiation, maturation, programming) after APEC infection. Here, we study gene expression in the bone marrow between infected and non-infected animals, and between infected animals with mild (resistant) versus severe (susceptible) pathology, at two times post-infection.

Results

We sequenced 24 bone marrow RNA libraries generated from the six different treatment groups with four replicates each, and obtained an average of 22 million single-end, 100-bp reads per library. Genes were detected as differentially expressed (DE) between APEC treatments (mild pathology, severe pathology, and mock-challenged) at a given time point, or DE between 1 and 5 days post-infection (dpi) within the same treatment group. Results demonstrate that many immune cells, genes and related pathways are key contributors to the different responses to APEC infection between susceptible and resistant birds and between susceptible and non-challenged birds, at both times post-infection. In susceptible birds, lymphocyte differentiation, proliferation, and maturation were greatly impaired, while the innate and adaptive immune responses, including dendritic cells, monocytes and killer cell activity, TLR- and NOD-like receptor signaling, as well as T helper cells and many cytokine activities, were markedly enhanced. The resistant birds’ immune system, however, was similar to that of non-challenged birds.

Conclusion

The DE genes in the immune cells and identified signaling models are representative of activation and resolution of infection in susceptible birds at both post-infection days. These novel results characterizing transcriptomic response to APEC infection reveal that there is combinatorial activity of multiple genes controlling myeloid cells, and B and T cell lymphopoiesis, as well as immune responses occurring in the bone marrow in these early stages of response to infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1850-4) contains supplementary material, which is available to authorized users.

Suppression of Th2 and Tfh immune reactions by Nr4a receptors in mature T reg cells

Sekiya et al. demonstrate that deletion of the nuclear orphan receptor Nr4a in T reg cells results in a fatal systemic immunopathology due to abrogated suppressive capability in limiting Th2 and Tfh conversion.

Regulatory T (T reg) cells are central mediators of immune suppression. As such, T reg cells are characterized by a distinct pattern of gene expression, which includes up-regulation of immunosuppressive genes and silencing of inflammatory cytokine genes. Although an increasing number of transcription factors that regulate T reg cells have been identified, the mechanisms by which the T reg cell–specific transcriptional program is maintained and executed remain largely unknown. The Nr4a family of nuclear orphan receptors, which we recently identified as essential for the development of T reg cells, is highly expressed in mature T reg cells as well, suggesting that Nr4a factors play important roles even beyond T reg cell development. Here, we showed that deletion of Nr4a genes specifically in T reg cells caused fatal systemic immunopathology. Nr4a-deficient T reg cells exhibited global alteration of the expression of genes which specify the T reg cell lineage, including reduction of Foxp3 and Ikzf4. Furthermore, Nr4a deficiency abrogated T reg cell suppressive activities and accelerated conversion to cells with Th2 and follicular helper T (Tfh) effector-like characteristics, with heightened expression of Th2 and Tfh cytokine genes. These findings demonstrate that Nr4a factors play crucial roles in mature T reg cells by directly controlling a genetic program indispensable for T reg cell maintenance and function.

Allogeneic mesenchymal stem cells inhibited T follicular helper cell generation in rheumatoid arthritis

T follicular helper (Tfh) cells provide help for antigen-specific B cells. We have previously shown that Tfh cell frequency was increased and associated with auto-antibodies in patients with rheumatoid arthritis (RA), suggesting a possible involvement of Tfh cells in its pathogenesis. Mesenchymal stem cells (MSCs) represent a promising alternative cell therapy for RA by modulating T and B cell activation and proliferation. However, it remains unknown whether MSCs have immunoregulation on Tfh cells. In this paper, we have demonstrated that allogeneic MSCs could suppress Tfh cell differentiation in RA patients partly via the production of indoleamine 2,3-dioxygenase (IDO). IFNγ generated from Tfh cell differentiation system induced IDO expression on MSCs. MSCs transplantation (MSCT) into collagen-induced arthritis (CIA) mice prevented arthritis progression by inhibiting both the number and function of Tfh cells in vivo. These findings reveal a novel suppressive function of MSCs in Tfh cells, which has implication in understanding the underlying mechanisms of the immunotherapeutic effects of MSCs on RA patients.

Follicular T helper cells and humoral reactivity in kidney transplant patients

Memory B cells play a pivotal role in alloreactivity in kidney transplantation. Follicular T helper (Tfh) cells play an important role in the differentiation of B cells into immunoglobulin-producing plasmablasts [through interleukin (IL)-21]. It is unclear to what extent this T cell subset regulates humoral alloreactivity in kidney transplant patients, therefore we investigated the absolute numbers and function of peripheral Tfh cells (CD4(POS) CXCR5(POS) T cells) in patients before and after transplantation. In addition, we studied their relationship with the presence of donor-specific anti-human leucocyte antigen (HLA) antibodies (DSA), and the presence of Tfh cells in rejection biopsies. After transplantation peripheral Tfh cell numbers remained stable, while their IL-21-producing capacity decreased under immunosuppression. When isolated after transplantation, peripheral Tfh cells still had the capacity to induce B cell differentiation and immunoglobulin production, which could be inhibited by an IL-21-receptor-antagonist. After transplantation the quantity of Tfh cells was the highest in patients with pre-existent DSA. In kidney biopsies taken during rejection, Tfh cells co-localized with B cells and immunoglobulins in follicular-like structures. Our data on Tfh cells in kidney transplantation demonstrate that Tfh cells may mediate humoral alloreactivity, which is also seen in the immunosuppressed milieu.

Absence of surrogate light chain results in spontaneous autoreactive germinal centres expanding V(H)81X-expressing B cells

Random recombination of antibody heavy- and light-chain genes results in a diverse B-cell receptor (BCR) repertoire including self-reactive BCRs. However, tolerance mechanisms that prevent the development of self-reactive B cells remain incompletely understood. The absence of the surrogate light chain, which assembles with antibody heavy chain forming a pre-BCR, leads to production of antinuclear antibodies (ANAs). Here we show that the naive follicular B-cell pool is enriched for cells expressing prototypic ANA heavy chains in these mice in a non-autoimmune background with a broad antibody repertoire. This results in the spontaneous formation of T-cell-dependent germinal centres that are enriched with B cells expressing prototypic ANA heavy chains. However, peripheral tolerance appears maintained by selection thresholds on cells entering the memory B-cell and plasma cell pools, as exemplified by the exclusion of cells expressing the intrinsically self-reactive V(H)81X from both pools.

MF59 Mediates Its B Cell Adjuvanticity by Promoting T Follicular Helper Cells and Thus Germinal Center Responses in Adult and Early Life

The early life influenza disease burden calls for more effective vaccines to protect this vulnerable population. Influenza vaccines including the MF59 oil-in-water adjuvant induce higher, broader, and more persistent Ab responses in adults and particularly in young, through yet undefined mechanisms. In this study, we show that MF59 enhances adult murine IgG responses to influenza hemagglutinin (HA) by promoting a potent T follicular helper cells (TFH) response, which directly controls the magnitude of the germinal center (GC) B cell response. Remarkably, this enhancement of TFH and GC B cells is already fully functional in 3-wk-old infant mice, which were fully protected by HA/MF59 but not HA/PBS immunization against intranasal challenge with the homologous H1N1 (A/California/7/2009) strain. In 1-wk-old neonatal mice, MF59 recruits and activates APCs, efficiently induces CD4(+) effector T cells and primes for enhanced infant responses but induces few fully functional TFH cells, which are mostly follicular regulatory T cells, and poor GC and anti-HA responses. The B cell adjuvanticity of MF59 appears to be mediated by the potent induction of TFH cells which directly controls GC responses both in adult and early life, calling for studies assessing its capacity to enhance the efficacy of influenza immunization in young infants.

Increased expression of transcription factor Bcl-6 in chronic rhinosinusitis with nasal polyps

B cell activation and excessive immunoglobulin (Ig) production were suggested as the key molecular events of chronic rhinosinusitis with nasal polyp (CRSwNP). However, whether T follicular cells (Tfh cells) were involved in this process has not been documented. In this study, 22 CRSwNP patients and 12 normal controls were enrolled, Bcl-6 (the key transcription factor for Tfh cell differentiation) immunoreactivity was examined by immunohistochemical staining, and the mRNA and protein expression of Bcl-6 and IL-21 was examined using qPCR, ELISA and Western blot, respectively. Moreover, the frequencies of Bcl-6(+)CD4(+) cells (Tfh cells) in polyp tissues and normal controls were measured by flow cytometry. We found that Bcl-6 mRNA and protein levels, as well as the frequencies of Bcl-6(+)CD4(+) cells were significantly increased in polyp tissues compared with normal controls. The frequencies of Bcl-6(+)CD4(+) cells were found to be significantly associated with B cell cluster formation, tissue eosinophilia, asthma comorbidity and polyp recurrence. These findings thus added a new insight into the molecular mechanisms underlying CRSwNP and raise the possibility that Tfh cells could be a novel therapeutic target for difficult-to-treat CRSwNP.

Dendritic cells and B cells: unexpected partners in Th2 development

Although we have known for decades that B cells contribute to immune responses by secreting Ab, it is now clear that they are more than simply factories for Ig production, and they also play key roles as modulators of T cell-dependent immunity. Indeed, the evidence showing that Ag-presenting and cytokine-producing B cells can alter the magnitude and quality of CD4 T cell responses continues to grow. In this article, we review the data showing that B cells, working in partnership with dendritic cells, regulate the development of Th2 cells and the subsequent allergic response.

The Differentiation of CD4(+) T-Helper Cell Subsets in the Context of Helminth Parasite Infection

Helminths are credited with being the major selective force driving the evolution of the so-called “type 2” immune responses in vertebrate animals, with their size and infection strategies presenting unique challenges to the immune system. Originally, type 2 immune responses were defined by the presence and activities of the CD4⁺ T-helper 2 subset producing the canonical cytokines IL-4, IL-5, and IL-13. This picture is now being challenged by the discovery of a more complex pattern of CD4⁺ T-helper cell subsets that appear during infection, including Tregs, Th17, Tfh, and more recently, Th22, Th9, and ThGM. In addition, a clearer view of the mechanisms by which helminths and their products selectively prime the CD4⁺ T-cell subsets is emerging. In this review, we have focused on recent data concerning the selective priming, differentiation, and functional role of CD4⁺ T-helper cell subsets in the context of helminth infection. We argue for a re-evaluation of the original Th2 paradigm and discuss how the observed plasticity of the T-helper subsets may enable the parasitized host to achieve an appropriate compromise between elimination, tissue repair, containment, and pathology.

Progression of autoimmune hepatitis is mediated by IL-18-producing dendritic cells and hepatic CXCL9 expression in mice

Clinical manifestations of autoimmune hepatitis (AIH) range from mild chronic to acute, sometimes fulminant hepatitis. However, it is unknown how the progression to fatal hepatitis occurs. We developed a mouse model of fatal AIH by inducing a concurrent loss of forkhead box P3(+) regulatory T cells and programmed cell death-1 (PD-1)-mediated signaling. In this model, dysregulated follicular helper T cells in the spleen are responsible for the induction, and the C-C chemokine receptor 6/C-C chemokine ligand 20 axis is crucial for the migration of these T cells into the liver. Using this fatal AIH model, we aimed to clarify key molecules triggering fatal AIH progression. During progression, T-bet together with interferon (IFN)-γ and C-X-C chemokine receptor (CXCR)3 were highly expressed in the inflamed liver, suggesting helper T (Th)1-type inflammation. T cells that dominantly expanded in the spleen and the inflamed liver were CXCR3-expressing CD8(+) T cells; depletion of these CD8(+) T cells suppressed AIH progression. Expression of one CXCR3 ligand, chemokine (C-X-C motif) ligand (CXCL)9, was elevated in the liver. CXCL9-expressing macrophages/Kupffer cells were colocalized with infiltrating T cells, and in vivo administration of anti-CXCL9 suppressed AIH progression. In addition, serum levels of interleukin (IL)-18, but not IL-1β, were elevated during progression, and dendritic cells in the spleen and liver highly produced IL-18. In vivo administration of anti-IL-18R suppressed the increase of splenic CXCR3(+) T cells and the progression to fatal AIH. Moreover, tumor necrosis factor alpha, but not IFN-γ, was involved in up-regulating CXCL9 in the liver and for increased serum levels of IL-18.

CONCLUSION

These data suggest that, in our mouse model, fatal progression of AIH is mediated by IL-18-dependent differentiation of T cells into Th1 cells and effector T cells, respectively, and that CXCR3-CXCL9 axis-dependent migration of those T cells is crucial for fatal progression.

Frequency of CD4+CXCR5+ TFH cells in patients with hepatitis b virus-associated membranous nephropathy

The frequency of different subsets of CD4(+)CXCR5(+) TFH cells and serum cytokine levels were analyzed in a total of 14 patients with newly diagnosed hepatitis B virus-associated membranous nephropathy (HBV-MN), 12 individuals with immune-tolerant HBV infection (HBV-IT) and 12 healthy controls (HC). Serum cytokine levels were measured before and 10-12 weeks after treatment. Significantly higher frequency of CD4(+)CXCR5(+), CD4(+)CXCR5(+)ICOS(+) and CD4(+)CXCR5(+)PD-1(+) TFH cells, and higher serum levels of IL-17A, IFN-γ, IL-2, IL-10, IL-4 and IL-21 were detected in HBV-MN patients compared to the HC. The percentage of CD4(+)CXCR5(+) TFH cells and serum IL-21 level in HBV-MN patients were also higher than the HBV-IT. The percentage of CD4(+)CXCR5(+) TFH cell was negatively correlated with the value of eGFR, and the percentage of CD4(+)CXCR5(+)ICOS(+) TFH cells was positively correlated with the 24-h urinary protein concentration. Notably, the percentage of CD4(+)CXCR5(+)PD-1(+) TFH cells was positively correlated with serum IL-21 level and 24-h urinary protein concentration. Treatment with prednisone or/and immunosuppressive drugs significantly reduced the frequency of CD4(+)CXCR5(+), CD4(+)CXCR5(+)PD-1(+) TFH cells and serum IL-21 level, but increased IL-4 and IL-10 levels in the patients. CD4(+)CXCR5(+) TFH cells, especially CD4(+)CXCR5(+)PD-1(+) TFH cells may participate in the pathogenesis of HBV-MN.

Increased frequency of circulating follicular helper T cells in patients with ankylosing spondylitis

OBJECTIVE

The relationship between circulating follicular helper T (Tfh) cells and ankylosing spondylitis (AS) remains unclear. The aims of our study were to measure the levels of circulating Tfh cells and several related parameters in patients with AS, and examine the correlation of these factors with disease activity.

METHODS

We designated CD4 + CXCR5 + ICOS+ T cells as circulating Tfh cells. The percentage of circulating Tfh cells was detected using flow cytometry. Plasma IL-21 and immunoglobulin (IgA, IgM, and IgG) levels were quantified using enzyme-linked immunosorbent assay in 60 AS patients and 60 healthy controls (HC).

RESULTS

The percentage of circulating Tfh cells was increased in AS patients compared with that in HC. As AS patients were divided into active and inactive groups, the percentage of circulating Tfh cells was significantly increased in active group compared with both inactive group and HC. Plasma IL-21 and immunoglobulin levels were elevated in AS patients, and the differences were significant except IgG. In addition, the percentage of circulating Tfh cells was positively correlated with Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), and plasma IL-21 levels were positively correlated with plasma immunoglobulin levels. But neither circulating Tfh cells nor BASDAI was significantly correlated with plasma IL-21 and immunoglobulin levels in AS patients, with the exception of significant correlation between BASDAI and plasma IgM levels in active AS patients.

CONCLUSION

Our study has shown the increased percentage of circulating Tfh cells correlated with disease activity, and the high plasma IL-21 levels were associated with high plasma immunoglobulin levels in patients with AS, indicating that the circulating Tfh cells may be associated with the development of AS.

Human metapneumovirus SH and G glycoproteins inhibit macropinocytosis-mediated entry into human dendritic cells and reduce CD4+ T cell activation

Human metapneumovirus (HMPV) is a major etiologic agent of respiratory disease worldwide. HMPV reinfections are common in healthy adults and children, suggesting that the protective immune response to HMPV is incomplete and short-lived. We used gene-deletion viruses to evaluate the role of the attachment G and small hydrophobic SH glycoproteins on virus uptake by primary human monocyte-derived dendritic cells (MDDC) in vitro and on subsequent MDDC maturation and activation of autologous T cells. HMPV with deletion of G and SH (ΔSHG) exhibited increased infectivity but had little effect on MDDC maturation. However, MDDC stimulated with ΔSHG induced increased proliferation of autologous Th1-polarized CD4(+) T cells. This effect was independent of virus replication. Increased T cell proliferation was strictly dependent on contact between virus-stimulated MDDC and CD4(+) T cells. Confocal microscopy revealed that deletion of SH and G was associated with an increased number of immunological synapses between memory CD4(+) T cells and virus-stimulated MDDC. Uptake of HMPV by MDDC was found to be primarily by macropinocytosis. Uptake of wild-type (WT) virus was reduced compared to that of ΔSHG, indicative of inhibition by the SH and G glycoproteins. In addition, DC-SIGN-mediated endocytosis provided a minor alternative pathway that depended on SH and/or G and thus operated only for WT. Altogether, our results show that SH and G glycoproteins reduce the ability of HMPV to be internalized by MDDC, resulting in a reduced ability of the HMPV-stimulated MDDC to activate CD4(+) T cells. This study describes a previously unknown mechanism of virus immune evasion.

IMPORTANCE

Human metapneumovirus (HMPV) is a major etiologic agent of respiratory disease worldwide. HMPV reinfections are common in healthy adults and children, suggesting that the protective immune response to HMPV is incomplete and short-lived. We found that HMPV attachment G and small hydrophobic SH glycoproteins reduce the ability of HMPV to be internalized by macropinocytosis into human dendritic cells (DC). This results in a reduced ability of the HMPV-stimulated DC to activate Th1-polarized CD4(+) T cells. These results contribute to a better understanding of the nature of incomplete protection against this important human respiratory virus, provide new information on the entry of HMPV into human cells, and describe a new mechanism of virus immune evasion.

Costimulation blockade alters germinal center responses and prevents antibody-mediated rejection

De novo donor-specific antibody (DSA) after organ transplantation promotes antibody-mediated rejection (AMR) and causes late graft loss. Previously, we demonstrated that depletion using anti-CD3 immunotoxin combined with tacrolimus and alefacept (AMR regimen) reliably induced early DSA production with AMR in a nonhuman primate kidney transplant model. Five animals were assigned as positive AMR controls, four received additional belatacept and four received additional anti-CD40 mAb (2C10R4). Notably, production of early de novo DSA was completely attenuated with additional belatacept or 2C10R4 treatment. In accordance with this, while positive controls experienced a decrease in peripheral IgM(+) B cells, bela- and 2C10R4-added groups maintained a predominant population of IgM(+) B cells, potentially indicating decreased isotype switching. Central memory T cells (CD4(+) CD28(+) CD95(+)) as well as PD-1(hi) CD4(+) T cells were decreased in both bela-added and 2C10R4-added groups. In analyzing germinal center (GC) reactions in situ, lymph nodes further revealed a reduction of B cell clonal expansion, GC-follicular helper T (Tfh) cells, and IL-21 production inside GCs with additional belatacept or 2C10R4 treatment. Here we provide evidence that belatacept and 2C10R4 selectively suppresses the humoral response via regulating Tfh cells and prevents AMR in this nonhuman primate model.

Myor/ABF-1 mRNA [corrected] Expression Marks Follicular Helper T Cells but Is Dispensable for Tfh Cell Differentiation and Function In Vivo

Follicular T helper cells (Tfh) are crucial for effective antibody responses and long term T cell-dependent humoral immunity. Although many studies are devoted to this novel T helper cell population, the molecular mechanisms governing Tfh cell differentiation have yet to be characterized. MyoR/ABF-1 is a basic helix-loop-helix transcription factor that plays a role in the differentiation of the skeletal muscle and Hodgkin lymphoma. Here we show that MyoR mRNA is progressively induced during the course of Tfh-like cell differentiation in vitro and is expressed in Tfh responding to Alum-precipitated antigens in vivo. This expression pattern suggests that MyoR could play a role in the differentiation and/or function of Tfh cells. We tested this hypothesis using MyoR-deficient mice and found this deficiency had no impact on Tfh differentiation. Hence, MyoR-deficient mice developed optimal T-dependent humoral responses to Alum-precipitated antigens. In conclusion, MyoR is a transcription factor selectively up-regulated in CD4 T cells during Tfh cell differentiation in vitro and upon response to alum-protein vaccines in vivo, but the functional significance of this up-regulation remains uncertain.

Immunologic features of Cornelia de Lange syndrome

OBJECTIVES

Cornelia de Lange syndrome (CdLS) is a genetic syndrome with multisystem abnormalities. Infections are a significant cause of morbidity and mortality. The goals of our study were to identify the frequency and types of infections in CdLS and to determine if underlying immunodeficiency contributes to the clinical spectrum of this syndrome.

METHODS

We assessed infectious histories in 45 patients with CdLS and evaluated conventional immunologic screening tests in 27 patients. Among these 27 subjects, additional phenotypic enumeration of T-cell subsets, expression of activation markers in T cells, and production of cytokines in response to T-cell stimulants were studied in 12 CdLS subjects compared with 12 normal case control subjects.

RESULTS

Recurrent infections were reported at high frequency in CdLS patients and included chronic ear infections (53%), chronic viral respiratory infections (46%), pneumonia (42%), sinus infections (33%), oral candidiasis (13%), sepsis (6%), and bacterial skin infections (4%). Full immune evaluation in 27 subjects led to identification of 9 cases of antibody deficiency syndrome in patients with severe forms of CdLS. Subjects with CdLS had decreased percentages of T regulatory cells and T follicular helper cells compared with normal control subjects (P < .05).

CONCLUSIONS

This study identified for the first time a high frequency of antibody deficiency in CdLS subjects, indicating a critical need for screening and management of immunodeficiency in CdLS patients with a history of well-documented severe or recurrent infections. Furthermore, our results indicate that impaired T-cell populations may be associated with antibody deficiency in CdLS.

STAT3 signaling induces the differentiation of human ICOS(+) CD4 T cells helping B lymphocytes

The generation of high-affinity antibodies and the development of B cell memory are dependent on the help provided by CD4 T cells. Mouse studies indicate that STAT3 signaling in CD4 T cells promotes the acquisition of the B cell help function. However, the role of STAT3 in humans has been controversial. In this study, we show that IL-6 and other STAT3 activating cytokines (IL-21 and IL-27) induce the differentiation of CD4 T cells promoting antibody production by B cells. The acquisition of B cell stimulating properties by naive cord blood CD4 T cells required the STAT3-dependent expression of ICOS and IL-21. Gene reporter and ChIP experiments unambiguously demonstrated that upon IL-6 stimulation, STAT3 induces the transcription of the ICOS gene through direct recruitment to the proximal promoter region indicating that STAT3 acts in part through the direct activation of the ICOS gene.

Follicular helper T Cells (Tfh) and IL-21 involvement in the pathogenesis of bullous pemphigoid

The pathogenesis of bullous pemphigoid (BP) is characterized by the T cell-dependent production of autoantibodies. Recent studies have indicated that follicular T helper cells (Tfh), the key modulator of B cell activation and autoantibody production, are critical in the development of several autoimmune diseases. Tfh cells perform their functions via IL-21, their hallmark cytokine. In the present study, the frequencies of Tfh cells were investigated in the peripheral blood samples of BP patients to evaluate whether Tfh cells involve in this clinical entity. Significantly higher Tfh cell counts were observed in the peripheral blood of BP patients than those in healthy controls (median: 11.25% vs. 4.95%, respectively; P<0.001). Additionally, the serum IL-21 levels in BP patients were higher than those of the healthy controls (median: 103.98 pg/mL vs 46.77 pg/mL, respectively; P<0.001). The frequencies of Tfh cells and IL-21 levels were both positively correlated with anti-BP180-NC16A autoantibody titers (R = 0.712, P<0.01 and R = 0.578, P = 0.030, respectively). After effective therapy, the frequencies of Tfh cells as well as the serum IL-21 levels in BP patients decreased along with clinical improvement. Most importantly, Tfh depleted CD4(+) T cells and anti-IL-21 neutralization antibody could inhibit the T cell-induced B cell activation and secretion of BP autoantibody in vitro. Those results suggest that Tfh cells play an important role in autoantibody production and are involved in the pathogenesis of BP.

Splenectomy prolongs the effects of corticosteroids in mouse models of autoimmune hepatitis

BACKGROUND & AIMS

Most patients with autoimmune hepatitis (AIH) initially respond to treatment with corticosteroids but often experience a relapse after treatment is withdrawn. BALB/c mice with disruption of programmed cell death 1 (PD-1(-/-) mice) that undergo thymectomy 3 days after birth develop a deregulated immune system, have reduced numbers of Foxp3(+) regulatory T cells, and develop fulminant hepatic failure that resembles acute-onset AIH in humans. We examined whether splenectomy overcomes corticosteroid insufficiency and reduces the severity of AIH in these mice. We also developed a mouse model of chronic AIH to investigate the effects of splenectomy.

METHODS

After thymectomy, BALB/c PD-1(-/-) mice were treated with dexamethasone before or after induction of AIH; splenectomy was performed in mice that had and had not been treated with dexamethasone. Neonatal C57BL/6 PD-1(-/-) mice underwent thymectomy to create a model of chronic AIH.

RESULTS

Injection of dexamethasone before or after induction of AIH prevented development of fatal AIH in BALB/c PD-1(-/-) mice. However, injection of dexamethasone after induction of AIH did not suppress splenic production of follicular helper T cells, and discontinuation of dexamethasone led to a relapse of AIH. Splenectomy (even without administration of dexamethasone) prevented AIH. Neonatal C57BL/6 PD-1(-/-) mice that underwent thymectomy developed chronic hepatitis with fibrosis and hypergammaglobulinemia and produced antinuclear antibodies; AIH was found to be induced in the spleen. Splenectomy reduced liver inflammation in these mice and in BALB/c PD-1(-/-) mice with AIH.

CONCLUSIONS

AIH can be induced in mice via disruption of PD-1 and thymectomy; these cause the same disruptions in immune regulation in BALB/c and C57BL/6 mice but produce different phenotypes. Splenectomy overcomes corticosteroid insufficiency in mice and prolongs the effects of dexamethasone.

Specificity through cooperation: BATF-IRF interactions control immune-regulatory networks

Basic leucine zipper transcription factor ATF-like (BATF), BATF2 and BATF3 belong to the activator protein 1 (AP-1) family of transcription factors, which regulate numerous cellular processes. Initially, BATF family members were thought to function only as inhibitors of AP-1-driven transcription, but recent studies have uncovered that these factors have unique, non-redundant and positive transcriptional activities in dendritic cells, B cells and T cells. The question of how BATF and BATF3 - which lack a transcriptional activation domain, unlike the AP-1 factors FOS and JUN - can exert unique positive transcriptional specificity has now been answered by the discovery that BATF molecules interact with members of the interferon-regulatory factor (IRF) family. The capacity of the BATF leucine zipper regions to mediate dimerization with AP-1 factors and also to define cooperative interactions with heterologous factors explains both the positive transcriptional activity of BATF proteins and how they activate distinct sets of target genes compared with FOS.

The role of T cell immunity in HIV-1 infection

The interplay between the T cell immune response and human immunodeficiency virus (HIV)-1 largely determines the outcome of infection. Typically, the virus overcomes the immune defences leading to a gradual decline in function that permits the development of disease. In recent years, a concerted effort in comparing T cell responses between 'controllers' and 'progressors' is beginning to identify the T cell subsets and factors that affect disease progression related to the effector functions of both CD4 and CD8 T cells. These efforts are providing opportunities for development of novel therapies and vaccines.

Fyn kinase is required for optimal humoral responses

The generation of antigen-specific antibodies and the development of immunological memory require collaboration between B and T cells. T cell-secreted IL-4 is important for B cell survival, isotype switch to IgG1 and IgE, affinity maturation, and the development of germinal centers (GC). Fyn, a member of the Src family tyrosine kinase, is widely expressed in many cell types, including lymphocytes. This kinase is known to interact with both the B cell and T cell receptor (BCR and TCR, respectively). While Fyn deletion does not impair the development of immature T cells and B cells, TCR signaling is altered in mature T cells. The current study demonstrates that Fyn deficient (KO) B cells have impaired IL-4 signaling. Fyn KO mice displayed low basal levels of IgG1, IgE and IgG2c, and delayed antigen-specific IgG1 and IgG2b production, with a dramatic decrease in antigen-specific IgG2c following immunization with a T-dependent antigen. Defects in antibody production correlated with significantly reduced numbers of GC B cells, follicular T helper cells (T_FH), and splenic plasma cells (PC). Taken together, our data demonstrate that Fyn kinase is required for optimal humoral responses.

Simian immunodeficiency virus infects follicular helper CD4 T cells in lymphoid tissues during pathogenic infection of pigtail macaques

T follicular helper (Tfh) cells are a specialized subset of memory CD4(+) T cells that are found exclusively within the germinal centers of secondary lymphoid tissues and are important for adaptive antibody responses and B cell memory. Tfh cells do not express CCR5, the primary entry coreceptor for both human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), and therefore, we hypothesized that these cells would avoid infection. We studied lymph nodes and spleens from pigtail macaques infected with pathogenic strain SIVmac239 or SIVmac251, to investigate the susceptibility of Tfh cells to SIV infection. Pigtail macaque PD-1(high) CD127(low) memory CD4(+) T cells have a phenotype comparable to that of human Tfh cells, expressing high levels of CXCR5, interleukin-21 (IL-21), Bcl-6, and inducible T cell costimulator (ICOS). As judged by either proviral DNA or cell-associated viral RNA measurements, macaque Tfh cells were infected with SIV at levels comparable to those in other CD4(+) memory T cells. Infection of macaque Tfh cells was evident within weeks of inoculation, yet we confirmed that Tfh cells do not express CCR5 or either of the well-known alternative SIV coreceptors, CXCR6 and GPR15. Mutations in the SIV envelope gp120 region occurred in chronically infected macaques but were uniform across each T cell subset investigated, indicating that the viruses used the same coreceptors to enter different cell subsets. Early infection of Tfh cells represents an unexpected focus of viral infection. Infection of Tfh cells does not interrupt antibody production but may be a factor that limits the quality of antibody responses and has implications for assessing the size of the viral reservoir.

Follicular T-cell lymphoma: a member of an emerging family of follicular helper T-cell derived T-cell lymphomas

Unlike B-cell lymphomas, where knowledge of normal B-cell origin and differentiation has greatly contributed to their classification, the current classification of peripheral T-cell lymphomas is limited by a lack of understanding of their cellular origin. In the current World Health Organization classification of lymphomas, follicular T-cell lymphoma was formally recognized as a morphologic variant of peripheral T-cell lymphoma, not otherwise specified. There is growing evidence, however, that follicular T-cell lymphoma may be a unique clinicopathologic entity based on its morphologic features and derivation from follicular helper T-cells. In addition, there are abundant recent data supporting the concept that follicular helper T-cells can give rise to other types of T-cell lymphoma, including angioimmunoblastic T-cell lymphoma, primary cutaneous CD4+ small/medium T-cell lymphoma, and a subset of neoplasms, in addition to follicular T-cell lymphoma, currently classified as peripheral T-cell lymphoma, not otherwise specified. In this review, we focus primarily on the clinicopathologic, immunophenotypic, and molecular features of follicular T-cell lymphoma and discuss its potential relationship with other types of T-cell lymphoma thought to be derived from follicular helper T-cells.

B and T cells collaborate in antiviral responses via IL-6, IL-21, and transcriptional activator and coactivator, Oct2 and OBF-1

Transcriptional activator Oct2 and cofactor OBF-1 regulate B cell IL-6 to induce T cell production of IL-21, to support Tfh cell development in antiviral immunity.

A strong humoral response to infection requires the collaboration of several hematopoietic cell types that communicate via antigen presentation, surface coreceptors and their ligands, and secreted factors. The proinflammatory cytokine IL-6 has been shown to promote the differentiation of activated CD4⁺ T cells into T follicular helper cells (T_FH cells) during an immune response. T_FH cells collaborate with B cells in the formation of germinal centers (GCs) during T cell–dependent antibody responses, in part through secretion of critical cytokines such as IL-21. In this study, we demonstrate that loss of either IL-6 or IL-21 has marginal effects on the generation of T_FH cells and on the formation of GCs during the response to acute viral infection. However, mice lacking both IL-6 and IL-21 were unable to generate a robust T_FH cell–dependent immune response. We found that IL-6 production in follicular B cells in the draining lymph node was an important early event during the antiviral response and that B cell–derived IL-6 was necessary and sufficient to induce IL-21 from CD4⁺ T cells in vitro and to support T_FH cell development in vivo. Finally, the transcriptional activator Oct2 and its cofactor OBF-1 were identified as regulators of Il6 expression in B cells.

The role of costimulatory molecules in directing the functional differentiation of alloreactive T helper cells

Costimulatory molecules are a heterogenous group of cell surface molecules that act to amplify or counteract the initial activating signals provided to T cells from the T cell receptor following its interaction with an antigen/major histocompatibility complex, thereby influencing T cell differentiation and fate. Although costimulation was previously thought to be indispensable for T cell activation at all stages of development, it is now known that the requirements for costimulation, and the costimulatory molecules involved, vary according to the stage of T cell differentiation. The ability to influence T cell fate is of paramount interest in the field of transplantation as we seek therapeutic options that inhibit detrimental alloimmune responses whilst simultaneously promoting allograft tolerance. As with many immune mechanisms, there is a degree of functional overlap between certain costimulatory molecules, whereas some have diametrically opposite effects on different T cell subsets despite sharing common ligands. This is a critical point when considering these molecules as therapeutic targets in transplantation, as blockade of a costimulatory pathway, although desirable in itself, may prevent the ligation of an essential regulatory coinhibitory molecule. This review discusses the T helper cell lineages pertinent to transplantation and the costimulatory molecules involved in their differentiation.

IL-21 regulates the differentiation of a human γδ T cell subset equipped with B cell helper activity

Vγ9Vδ2 T lymphocytes recognize nonpeptidic antigens without presentation by MHC molecules and display pleiotropic features. Here we report that coculture of Vγ9Vδ2 cells with phosphoantigen and IL-21 leads to selective expression of the transcription repressor Bcl-6 and polarization toward a lymphocyte subset displaying features of follicular B-helper T (T_FH) cells. T_FH-like Vγ9Vδ2 cells have a predominant central memory (CD27⁺CD45RA⁻) phenotype and express ICOS, CD40L and CXCR5. Upon antigen activation, they secrete IL-4, IL-10 and CXCL13, and provide B-cell help for antibody production in vitro. Our findings delineate a subset of human Vγ9Vδ2 lymphocytes, which, upon interaction with IL-21-producing CD4 T_FH cells and B cells in secondary lymphoid organs, is implicated in the production of high affinity antibodies against microbial pathogens.

A regulatory role for IL-10 receptor signaling in development and B cell help of T follicular helper cells in mice

IL -10 is widely accepted as a survival, proliferation, and differentiation factor for B cells. However, IL-10 deficiency accelerates disease progression as the result of autoantibody production in many autoimmune disease models. It was demonstrated that T follicular helper cells (T(FH) cells) play a key role in helping B cells that are secreting Abs. In this study, we demonstrated a regulatory role for IL-10R signaling on the development and B cell help function of T(FH) cells in vitro and in vivo. IL-1R subunit β-deficient (Il10rb(-/-)) Th cells were able to differentiate more readily into T(FH) cells, as well as secrete more IL-21 and IL-17 compared with wild-type Th cell-derived T(FH) cells. Increased IL-21 and IL-17 contributed to the enhanced B cell help functions of T(FH) cells. Further experiments demonstrated that IL-6 and IL-23 from dendritic cells in Il10rb(-/-) mice contributed to the differentiation of naive Th cells into T(FH) cells, as well as the generation of IL-21- and IL-17-producing T(FH) cells. Our results provide useful information for clarifying the immunoregulatory mechanisms associated with IL-10 deficiency in certain autoimmune disease models. This information could also be of benefit for the development of vaccines.

RORγt-dependent IL-17A-producing cells in the pathogenesis of intestinal inflammation

The hypothesis of helper T (T(h))1/T(h)2 cytokine balance proposed by Mosmann and Coffman is often invoked to explain the development of inflammatory diseases, including inflammatory bowel diseases (IBD). Recently, however, a newly identified class of T(h) cells-T(h)17 cells, which produce T(h)17 family cytokines-has been recognized as an essential subpopulation in the development of almost all kinds of human and animal inflammatory diseases, rather than T(h)1 and T(h)2 cells. A representative T(h)17 family cytokine, interleukin (IL)-17A, is produced by not only T(h)17 cells, but also by other types of cells, such as T-cell receptor γδ T cells, natural killer (NK) T cells, NK cells, myeloid cells, and innate lymphoid cells, which may also be critically involved in the initiation and persistence of IBD. Here we review recent advances in the study of such IL-17A-producing cells in the pathogenesis of IBD.