Blood CD4+CD45RO+CXCR5+ T cells are decreased but partially functional in signal transducer and activator of transcription 3 deficiency

Monogenic Inborn Errors of Immunity with impaired IgG response to polysaccharide antigens but normal IgG levels and normal IgG response to protein antigens

In patients with severe and recurrent infections, minimal diagnostic workup to test for Inborn Errors of Immunity (IEI) includes a full blood count, IgG, IgA and IgM. Vaccine antibodies against tetanus toxoid are also frequently measured, whereas testing for anti-polysaccharide IgG antibodies and IgG subclasses is not routinely performed by primary care physicians. This basic approach may cause a significant delay in diagnosing monogenic IEI that can present with an impaired IgG response to polysaccharide antigens with or without IgG subclass deficiency at an early stage. Our article reviews genetically defined IEI, that may initially present with an impaired IgG response to polysaccharide antigens, but normal or only slightly decreased IgG levels and normal responses to protein or conjugate vaccine antigens. We summarize clinical, genetic, and immunological findings characteristic for these IEI. This review may help clinicians to identify patients that require extended immunologic and genetic evaluations despite unremarkable basic immunologic findings. We recommend the inclusion of anti-polysaccharide IgG antibodies as part of the initial routine work-up for possible IEI.

The Child with Elevated IgE and Infection Susceptibility

PURPOSE OF REVIEW

Over the last 13 years, the genetic etiologies have been determined for multiple conditions causing elevated serum IgE, infection susceptibilities, and variable other features. In this review, we discuss the clinical presentation, laboratory features, and genetics of these diseases caused by mutations in STAT3, DOCK8, PGM3, IL6ST, ZNF341, IL6R, IL6ST, CARD11, and CARD14, with particular focus given to STAT3LOF and DOCK8 deficiency.

RECENT FINDINGS

Defining the phenotype of each of these syndromes with high IgE and infection susceptibility shows that some have a pronounced connective tissue phenotype such as STAT3LOF and IL6ST deficiency, some have worse viral susceptibility such as DOCK8 deficiency and heterozygous LOF CARD11, and some have more severe allergy and eczema such as LOF CARD14. Studying these distinct but overlapping monogenic diseases will allow a better understanding of more common disease processes such as allergy, eczema, infection susceptibility, scoliosis, and aneurysm.

Regulation of the germinal center and humoral immunity by interleukin-21

Here we review the critical and non-redundant functions of IL-21 in regulating humoral immune responses. We particularly focus on studies in natura—from individuals from inborn errors of immunity that impact on IL-21 production and/or function.

Cytokines play critical roles in regulating the development, survival, differentiation, and function of immune cells. Cytokines exert their function by binding specific receptor complexes on the surface of immune cells and activating intracellular signaling pathways, thereby resulting in induction of specific transcription factors and regulated expression of target genes. While the function of cytokines is often fundamental for the generation of robust and effective immunity following infection or vaccination, aberrant production or function of cytokines can underpin immunopathology. IL-21 is a pleiotropic cytokine produced predominantly by CD4⁺ T cells. Gene-targeting studies in mice, in vitro analyses of human and murine lymphocytes, and the recent discoveries and analyses of humans with germline loss-of-function mutations in IL21 or IL21R have revealed diverse roles of IL-21 in immune regulation and effector function. This review will focus on recent advances in IL-21 biology that have highlighted its critical role in T cell–dependent B cell activation, germinal center reactions, and humoral immunity and how impaired responses to, or production of, IL-21 can lead to immune dysregulation.

T follicular helper cells are elevated in a rat model of autoimmune myocarditis

Myocarditis is an inflammatory disease of the myocardium that is associated with immune dysfunction. Earlier studies have suggested that T helper 1/2 cell imbalance plays an important role in the development of myocarditis, but the role of T follicular helper (Tfh) cells in the development of autoimmune myocarditis has not previously been reported. Here, we investigated this involvement by using a rat model of experimental autoimmune myocarditis (EAM). Inflammatory cell infiltration, myocardial structure destruction and tissue necrosis were observed in EAM myocardial tissues, and the percentages of CD4⁺ CXCR5⁺ Tfh cells and CD19⁺ B cells were both significantly higher in spleen and myocardial tissues of the EAM model as compared with the control group. Furthermore, the expression levels of interleukin-21, CXCL13 and myosin antibody were significantly higher in the serum of rats with EAM compared with the control group on days 14 and 35 after immunization. Fourteen or 35 days after immunization, the expression levels of interleukin-21 and CXCL13 were both significantly higher in myocardial tissues of rats with EAM as compared with the control group. Our findings suggest that Tfh cell balance is disrupted during the pathological process of autoimmune myocarditis.

The role of follicular T helper cells in the humoral alloimmune response after clinical organ transplantation

Over the past decade, antibody‐mediated or humoral rejection in combination with development of de novo donor‐specific antibodies (DSA) has been recognized as a distinct and common cause of transplant dysfunction and is responsible for one‐third of the failed allografts. Detailed knowledge of the mechanisms that initiate and maintain B‐cell driven antidonor reactivity is required to prevent and better treat this antidonor response in organ transplant patients. Over the past few years, it became evident that this response largely depends on the actions of both T follicular helper (Tfh) cells and the controlling counterparts, the T follicular regulatory (Tfr) cells. In this overview paper, we review the latest insights on the functions of circulating (c)Tfh cells, their subsets Tfh1, Tfh2 and Tfh17 cells, IL‐21 and Tfr cells in antibody mediated rejection (ABMR). This may offer new insights in the process to reduce de novo DSA secretion resulting in a decline in the incidence of ABMR. In addition, monitoring these cell populations could be helpful for the development of biomarkers identifying patients at risk for ABMR and provide novel therapeutic drug targets to treat ABMR.

Circulating CXCR5+CD4+ T cells participate in the IgE accumulation in allergic asthma

The pathogenesis of allergic asthma is primarily characterized by abnormality in immunoglobin(Ig)E pathway, suggesting a possible role for follicular helper T cells (Tfh) in the genesis of excessive IgE accumulation. The blood chemokine (C-X-C motif) receptor 5 (CXCR)5+CD4+ T cells, known as "circulating" Tfh, share common functional characteristics with Tfh cells from germinal centers. The aim of this study was to determine the phenotypes and functions of circulating CXCR5+CD4+ T cells in allergic asthmatics. Here we found the frequency of the circulating CXCR5+CD4+ T cells was raised in allergic asthma compared with healthy control (HC). Phenotypic assays showed that activated circulating CXCR5+CD4+ T cells display the key features of Tfh cells, including invariably coexpressed programmed cell death (PD)-1 and inducible costimulator (ICOS). The frequency of interleukin IL-4+-, IL-21+-producing CXCR5+CD4+ T cells was increased in allergic asthma patients compared with HC. Furthermore, sorted circulating CXCR5+CD4+ T cells from allergic asthma patients boosted IgE production in coculture assay which could be inhibited by IL-4 or IL-21 blockage. Interestingly, IL-4+-, IL-21+-CXCR5+CD4+ T cells positively correlated with total IgE in the blood. Our data indicated that circulating CXCR5+CD4+ T cells may have a significant role in facilitating IgE production in allergic asthma patients.

STAT3 regulates cytotoxicity of human CD57+ CD4+ T cells in blood and lymphoid follicles

A subset of human follicular helper T cells (TFH) cells expresses CD57 for which no distinct function has been identified. We show that CD57+ TFH cells are universally PD-1^hi, but compared to their CD57- PD-1^hi counterparts, express little IL-21 or IL-10 among others. Instead, CD57 expression on TFH cells marks cytotoxicity transcriptional signatures that translate into only a weak cytotoxic phenotype. Similarly, circulating PD-1+ CD57+ CD4+ T cells make less cytokine than their CD57- PD-1+ counterparts, but have a prominent cytotoxic phenotype. By analysis of responses to STAT3-dependent cytokines and cells from patients with gain- or loss-of-function STAT3 mutations, we show that CD4+ T cell cytotoxicity is STAT3-dependent. TFH formation also requires STAT3, but paradoxically, once formed, PD-1^hi cells become unresponsive to STAT3. These findings suggest that changes in blood and germinal center cytotoxicity might be affected by changes in STAT3 signaling, or modulation of PD-1 by therapy.

Signal Transducer and Activator of Transcription 3 Control of Human T and B Cell Responses

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is activated downstream of many key cytokine receptors expressed by lymphocytes. As such, it plays a critical role in regulating B cells as well as CD4⁺ and CD8⁺ T cells. Patients with clinically significant immunodeficiency and immune dysregulation resulting from loss-of-function or gain-of-function mutations in STAT3 have been described. These individuals provide insight into the critical role of this transcription factor in the regulation of immune responses and the balance between effective immune protection and autoimmunity.

Follicular Helper T Cells in Systemic Lupus Erythematosus: Why Should They Be Considered as Interesting Therapeutic Targets?

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by B cell hyperactivity leading to the production of autoantibodies, some of which having a deleterious effect. Reducing autoantibody production thus represents a way of controlling lupus pathogenesis, and a better understanding of the molecular and cellular factors involved in the differentiation of B cells into plasma cells could allow identifying new therapeutic targets. Follicular helper T cells (T_FH) represent a distinct subset of CD4⁺ T cells specialized in providing help to B cells. They are required for the formation of germinal centers and the generation of long-lived serological memory and, as such, are suspected to play a central role in SLE. Recent advances in the field of T_FH biology have allowed the identification of important molecular factors involved in T_FH differentiation, regulation, and function. Interestingly, some of these T_FH-related molecules have been described to be dysregulated in lupus patients. In the present review, we give an overview of the aberrant expression and/or function of such key players in lupus, and we highlight their potential as therapeutic targets.

Human T Follicular Helper Cells in Primary Immunodeficiency: Quality Just as Important as Quantity

T follicular helper (Tfh) cells are a subset of effector CD4(+) T cells specialised to induce Ab production by B cells. This review highlights some of the recent advances in the field of human Tfh cells that have come from the study of primary immunodeficiencies. In particular it is increasingly evident that the quality of the Tfh cells that are generated, is just as important as the quantity.

Nasal IL-4(+)CXCR5(+)CD4(+) T follicular helper cell counts correlate with local IgE production in eosinophilic nasal polyps

BACKGROUND

Locally produced IgE contributes to the initiation and development of eosinophilic inflammation in eosinophilic nasal polyps independent of systemic atopy. However, whether CXCR5(+)CD4(+) T follicular helper (TFH) cells are involved in local IgE production at mucosal sites remains unexplored.

OBJECTIVE

We sought to explore the presence, phenotype, and function of CXCR5(+)CD4(+) TFH cells in eosinophilic nasal polyp tissues compared with noneosinophilic nasal polyp and control normal nasal tissues.

METHODS

TFH cell-surface phenotypes and subsets and B-cell subsets in nasal tissues and peripheral blood were studied by means of flow cytometry. Immunohistochemistry was used to detect the tissue location of TFH cells. Sorted nasal TFH cells and CXCR5(-) T cells were cultured with autologous naive B cells purified from blood.

RESULTS

Nasal TFH cells expressed inducible costimulator, programmed cell death protein 1, and the transcription factor B-cell lymphoma 6 (Bcl-6) at an intermediate level when compared with bona fide TFH cells in tonsils and circulating TFH cells. Although counts of total TFH cells and IL-21(+), IFN-γ(+), and IL-17(+) TFH cells were increased in both eosinophilic and noneosinophilic nasal polyp tissues compared with those in normal nasal tissues, IL-4(+) TFH cell counts were only increased in eosinophilic polyp tissues. IL-4 and IL-21 were involved in polyp TFH cell-induced IgE production from naive B cells, and nasal IL-4(+) TFH cell counts correlated highly with local IgE levels in vivo. IL-4(+)Bcl-6(+)CD4(+) TFH cells were identified in ectopic lymphoid structures in eosinophilic nasal polyps. TFH cells also positively correlated with germinal center B cells and plasma cells in nasal tissues.

CONCLUSION

Nasal IL-4(+) TFH cells might be involved in local IgE production in eosinophilic nasal polyps.

Pathophysiology of T follicular helper cells in humans and mice

Follicular helper T cells (TFH cells) compose a heterogeneous subset of CD4(+) T cells that induce the differentiation of B cells into plasma cells and memory cells. They are found within and in proximity to germinal centers in secondary lymphoid organs, and their memory compartment also circulates in the blood. Our knowledge on the biology of TFH cells has increased significantly during the past decade, largely as a result of mouse studies. However, recent studies on human TFH cells isolated from lymphoid organ and blood samples and recent observations on the developmental mechanism of human TFH cells have revealed both similarities and differences between human and mouse TFH cells. Here we present the similarities and differences between mouse and human lymphoid organ-resident TFH cells and discuss the role of TFH cells in response to vaccines and in disease pathogenesis.

T-cell STAT3 is required for the maintenance of humoral immunity to LCMV

STAT3 is a critical transcription factor activated downstream of cytokine signaling and is integral for the function of multiple immune cell types. Human mutations in STAT3 cause primary immunodeficiency resulting in impaired control of a variety of infections, including reactivation of latent viruses. In this study, we investigate how T-cell functions of STAT3 contribute to responses to viral infection by inducing chronic lymphocytic choriomeningitis virus (LCMV) infection in mice lacking STAT3 specifically in T cells. Although mice with conditional disruption of STAT3 in T cells were able to mount early responses to viral infection similar to control animals, including expansion of effector T cells, we found generation of T-follicular helper (Tfh) cells to be impaired. As a result, STAT3 T cell deficient mice produced attenuated germinal center reactions, and did not accumulate bone marrow virus specific IgG-secreting cells, resulting in failure to maintain levels of virus-specific IgG or mount neutralizing responses to LCMV in the serum. These effects were associated with reduced control of viral replication and prolonged infection. Our results demonstrate the importance of STAT3 in T cells for the generation of functional long-term humoral immunity to viral infections.

STAT3 is a central regulator of lymphocyte differentiation and function

Signalling in lymphocytes through cytokine receptors is critical for their development, activation and differentiation into effector cells that mediate protection against pathogens and provide the host with protective immunological memory. The essential role of cytokine signalling has been established not only by the generation and examination of gene-targeted mice, but also 'Experiments of Nature' whereby monogenic mutations cause primary immunodeficient conditions characterised by impaired immunity to infectious diseases due to compromised lymphocyte function. Mutations in STAT3 cause autosomal dominant hyper-IgE syndrome. Here, we will review how the study of STAT3-deficient individuals has revealed non-redundant functions of STAT3 and specific cytokines in human lymphocyte biology, and have delineated mechanisms underlying the distinct clinical features of autosomal dominant hyper-IgE syndrome.

Advances in basic and clinical immunology in 2013

A significant number of contributions to our understanding of primary immunodeficiencies (PIDs) in pathogenesis, diagnosis, and treatment were published in the Journal in 2013. For example, deficiency of mast cell degranulation caused by signal transducer and activator of transcription 3 deficiency was demonstrated to contribute to the difference in the frequency of severe allergic reactions in patients with autosomal dominant hyper-IgE syndrome compared with that seen in atopic subjects with similar high IgE serum levels. High levels of nonglycosylated IgA were found in patients with Wiskott-Aldrich syndrome, and these abnormal antibodies might contribute to the nephropathy seen in these patients. New described genes causing immunodeficiency included caspase recruitment domain 11 (CARD11), mucosa-associated lymphoid tissue 1 (MALT1) for combined immunodeficiencies, and tetratricopeptide repeat domain 7A (TTC7A) for mutations associated with multiple atresia with combined immunodeficiency. Other observations expand the spectrum of clinical presentation of specific gene defects (eg, adult-onset idiopathic T-cell lymphopenia and early-onset autoimmunity might be due to hypomorphic mutations of the recombination-activating genes). Newborn screening in California established the incidence of severe combined immunodeficiency at 1 in 66,250 live births. The use of hematopoietic stem cell transplantation for PIDs was reviewed, with recommendations to give priority to research oriented to establish the best regimens to improve the safety and efficacy of bone marrow transplantation. These represent only a fraction of significant research done in patients with PIDs that has accelerated the quality of care of these patients. Genetic analysis of patients has demonstrated multiple phenotypic expressions of immune deficiency in patients with nearly identical genotypes, suggesting that additional genetic factors, possibly gene dosage, or environmental factors are responsible for this diversity.

Naive and memory human B cells have distinct requirements for STAT3 activation to differentiate into antibody-secreting plasma cells

Long-lived antibody memory is mediated by the combined effects of long-lived plasma cells (PCs) and memory B cells generated in response to T cell-dependent antigens (Ags). IL-10 and IL-21 can activate multiple signaling pathways, including STAT1, STAT3, and STAT5; ERK; PI3K/Akt, and potently promote human B cell differentiation. We previously showed that loss-of-function mutations in STAT3, but not STAT1, abrogate IL-10- and IL-21-mediated differentiation of human naive B cells into plasmablasts. We report here that, in contrast to naive B cells, STAT3-deficient memory B cells responded to these STAT3-activating cytokines, differentiating into plasmablasts and secreting high levels of IgM, IgG, and IgA, as well as Ag-specific IgG. This was associated with the induction of the molecular machinery necessary for PC formation. Mutations in IL21R, however, abolished IL-21-induced responses of both naive and memory human B cells and compromised memory B cell formation in vivo. These findings reveal a key role for IL-21R/STAT3 signaling in regulating human B cell function. Furthermore, our results indicate that the threshold of STAT3 activation required for differentiation is lower in memory compared with naive B cells, thereby identifying an intrinsic difference in the mechanism underlying differentiation of naive versus memory B cells.

Human T follicular helper (Tfh) cells and disease

The generation of protective antibodies by B cells following natural infection or vaccination requires 'help' from CD4(+) T cells. T follicular helper (Tfh) cells are the specialized CD4(+) T cell subset that has evolved the appropriate mechanisms to induce the activation and differentiation of B cells into immunoglobulin (Ig) secreting cells. As such, appropriate control of Tfh cell generation and function is essential to human health as overactivation is likely to result in autoimmunity, whereas underactivation is often associated with immunodeficiency. Furthermore, an understanding of the regulation of these cells may be invaluable to improved vaccine development strategies. Traditionally Tfh cells have been identified by their anatomical location in secondary lymphoid tissues, which has hindered the study of these cells in humans as access to these tissues is often not feasible. However, recent studies have identified the circulating counterparts to tissue Tfh cells and with this has come a wealth of knowledge gained from the study of these cells in human disease. Here we review some of the recent developments on the role of human Tfh cells in health and disease.

Circulating TFH subset distribution is strongly affected in lupus patients with an active disease

Follicular helper T cells (T_FH) represent a distinct subset of CD4⁺ T cells specialized in providing help to B lymphocytes, which may play a central role in autoimmune diseases having a major B cell component such as systemic lupus erythematosus. Recently, T_FH subsets that share common phenotypic and functional characteristics with T_FH cells from germinal centers, have been described in the peripheral blood from healthy individuals. The aim of this study was to analyze the distribution of such populations in lupus patients. Circulating T_FH cell subsets were defined by multicolor flow cytometry as T_FH17 (CXCR3^-CCR6⁺), T_FH1 (CXCR3 ⁺ CCR6^-) or T_FH2 (CXCR3^-CCR6^-) cells among CXCR5 ⁺ CD45RA^-CD4⁺ T cells in the peripheral blood of 23 SLE patients and 23 sex and age-matched healthy controls. IL-21 receptor expression by B cells was analyzed by flow cytometry and the serum levels of IL-21 and Igs were determined by ELISA tests. We found that the T_FH2 cell subset frequency is strongly and significantly increased in lupus patients with an active disease (SLEDAI score>8), while the T_FH1 cell subset percentage is greatly decreased. The T_FH2 and T_FH1 cell subset frequency alteration is associated with the presence of high Ig levels and autoantibodies in patient’s sera. Moreover, the T_FH2 cell subset enhancement correlates with an increased frequency of double negative memory B cells (CD27^-IgD^-CD19⁺ cells) expressing the IL-21R. Finally, we found that IgE levels in lupus patients’ sera correlate with disease activity and seem to be associated with high T_FH2 cell subset frequency. In conclusion, our study describes for the first time the distribution of circulating T_FH cell subsets in lupus patients. Interestingly, we found an increased frequency of T_FH2 cells, which correlates with disease activity. Our results suggest that this subset might play a key role in lupus pathogenesis.