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Summary: The essential role of B cells is to produce protective immunoglobulins (Ig) that recognize, neutralize, and clear invading pathogens. This results from the integration of signals provided by pathogens or vaccines and the stimulatory microenvironment within sites of immune activation, such as secondary lymphoid tissues, that drive mature B cells to differentiate into memory B cells and antibody (Ab)‐secreting plasma cells. In this context, B cells undergo several molecular events including Ig class switching and somatic hypermutation that results in the production of high‐affinity Ag‐specific Abs of different classes, enabling effective pathogen neutralization and long‐lived humoral immunity. However, perturbations to these key signaling pathways underpin immune dyscrasias including immune deficiency and autoimmunity or allergy. Inborn errors of immunity that disrupt critical immune pathways have identified non‐redundant requirements for eliciting and maintaining humoral immune memory but concomitantly prevent immune dysregulation. Here, we will discuss our studies on human B cells, and how our investigation of cytokine signaling in B cells have identified fundamental requirements for memory B‐cell formation, Ab production as well as regulating Ig class switching in the context of protective versus allergic immune responses. [ABSTRACT FROM AUTHOR]

Background: Increasingly, patients with breast cancer undergo bilateral mastectomy (BLM). To the authors' knowledge, the magnitude of benefit is unknown.Methods: The authors used data from the Surveillance, Epidemiology, and End Results (SEER) program regarding all women diagnosed with American Joint Committee on Cancer stage 0 to stage III unilateral breast cancer in California from 1998 through 2015 and treated with BLM versus breast-conserving therapy including surgery and radiotherapy (BCT) or unilateral mastectomy (ULM). The authors measured relative risks of second contralateral breast cancer (CBC) and breast cancer death using Fine and Gray multivariable regression modeling adjusted for the competing risk of death and death from another cause, respectively, and potential confounding factors. Absolute excess risk of CBC was measured as the observed minus expected number of breast cancers in the general population divided by 10,000 person-years at risk.Results: Among 245,418 patients with a median follow-up of 6.7 years, 7784 patients (3.2%) developed CBC. Relative risks were lower after BLM (hazard ratio [HR], 0.10; 95% CI, 0.07-0.14) and higher after ULM (HR, 1.07; 95% CI, 1.02-1.13) versus BCT. Absolute excess risks were higher after BCT and ULM (5.0 and 13.6 more cases, respectively) compared with BLM (28.6 fewer cases). BLM reduced risk more among older women (38.0 fewer cases for women aged ≥50 years vs 17.9 fewer cases among women aged <50 years) but provided similar risk reduction across categories of tumor grade and tumor hormone receptor status. Compared with BCT, the risk of breast cancer death was equivalent after BLM (HR, 1.03; 95% CI, 0.96-1.11) and higher after ULM (HR, 1.21; 95% CI, 1.17-1.25).Conclusions: BLM may reduce second breast cancer risk by 34 to 43 cases per 10,000 person-years compared with other surgical procedures, but is not associated with a lower risk of death. Second breast cancers are rare, and their reduction should be weighed against the harms associated with BLM. [ABSTRACT FROM AUTHOR]

Inherited defects in genes encoding for proteins that are involved in the assembly and dynamics of the actin skeleton have increasingly been identified in patients presenting with primary immunodeficiencies. In this review, we summarize a subset of the recently described conditions, emphasizing the clinical features as well as the immunophenotype and pathophysiology. [ABSTRACT FROM AUTHOR]

Interleukin‐9 (IL‐9) producing CD4+ Th9 cells are a unique subset of effector cells involved in both health and disease. Th9 cells have been associated with protective immunity during parasitic infections with helminths, protozoans and extracellular pathogens, but implicated in disease states such as allergic asthma, atopic dermatitis, food allergy and autoimmune conditions including multiple sclerosis and ulcerative colitis. Here, we review the cytokine signaling pathways and downstream transcription factors required for IL‐9 expression and how human primary immunodeficiencies caused by monogenic mutations can help elucidate the complex requirements for human Th9 cell differentiation. Primary immunodeficiencies are a platform for investigating IL‐9 expression in primary human lymphocytes and by inference whether Th9 cells are implicated in the clinical phenotype characteristic of these patients. [ABSTRACT FROM AUTHOR]

T follicular helper (Tfh) cells have the important function of providing B-cell help for the induction of antigen-specific antibody production. As such, it is important to determine the factors that regulate the development, differentiation and function of Tfh cells. This review highlights some of the recent advances in our understanding of Tfh cell migration, Tfh cell memory and the origins and fate of circulating Tfh cells in the blood, that have been revealed from studies in humans and mice. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Regulated interactions between cells of the immune system facilitate the generation of successful immune responses, thereby enabling efficient neutralization and clearance of pathogens and the establishment of both cell- and humoral-mediated immunological memory. The corollary of this is that impediments to efficient cell-cell interactions, normally necessary for differentiation and effector functions of immune cells, underly the clinical features and disease pathogenesis of primary immunodeficiencies. In affected individuals, these defects manifest as impaired long-term humoral immunity and susceptibility to infection by specific pathogens. In this review, we discuss the importance of, and requirements for, effective interactions between B cells and T cells during the formation of CD4+ T follicular helper cells and the elicitation of cytotoxic function of virus-specific CD8+ T cells, as well as how these processes are abrogated in primary immunodeficiencies due to loss-of-function mutations in defined genes. [ABSTRACT FROM AUTHOR]

Summary It is well established that the generation of a high-affinity long-lived antibody response requires the presence of T cells, specifically CD4+ T cells. These CD4+ T cells support the generation of a germinal centre (GC) response where somatic hypermutation and affinity maturation take place leading to the generation of memory B cells and plasma cells, which provide long-lasting protection. Greater insight into the nature of the CD4+ T cells involved in this process was provided by two studies in 2000 that described CD4+ T cells residing in the B cell follicle that expressed CXCR5. As a result these cells were named follicular B helper T cells, now more commonly known as T follicular helper (Tfh) cells. Since then there has been enormous growth in our understanding of these cells, now considered a distinct T helper (Th) cell lineage that can arise from naive CD4+ T cells following activation. This review summarizes some of the most recent work that has characterized Tfh cells and the pathways that lead to their generation. [ABSTRACT FROM AUTHOR]

Effective B cell-mediated immunity, including the formation of germinal centers and the generation of high-affinity memory B cells and long-lived plasma cells, is dependent on CD4 T cells. Immunodeficiencies that present with defects in the antibody response have provided insights into the molecular mechanisms of B cell responses and the provision of T cell help. One such immunodeficiency is X-linked lymphoproliferative disease (XLP), which results from mutations in SH2D1A, the gene encoding SLAM-associated protein (SAP). Patients with XLP present with humoral defects characterized by hypogammaglobulinemia. We now know that SAP, through its signaling downstream of multiple members of the signaling lymphocytic activation molecule (SLAM) family of cell surface receptors, plays a crucial role in many aspects of this immune response. Here, we discuss the role of SAP in the generation of humoral immunity, particularly T cell-dependent antibody responses and the generation of germinal centers. [ABSTRACT FROM AUTHOR]

T follicular helper (TFH) cells are a specialized subset of CD4+ T cells that localize to B-cell follicles, where they are positioned to provide help for the induction of optimal humoral immune responses. Key features of TFH cells are the expressions of CXCR5, ICOS, interleukin (IL)-21 and BCL-6. The requirements for human TFH cell development are unknown. Here we show that IL-6, IL-12, IL-21 and IL-23 are capable of inducing IL-21 expression in naïve CD4+ T cells isolated from human tonsils, peripheral blood and cord blood. However, only IL-12 induced sustained expressions of CXCR5 and ICOS on these activated naïve CD4+ T cells, and endowed them with the ability to provide increased help to B cells for their differentiation into immunoglobulin-secreting cells. The effects of IL-12 were independent of interferon-γ and T-bet, and associated with upregulation of BCL-6 expression. Thus, these cytokines, particularly IL-12, are likely to act at an early stage during dendritic cell-mediated priming of naïve CD4+ T cells into a TFH cell fate, and thus underpin antibody-mediated immunity. [ABSTRACT FROM AUTHOR]

X-linked lymphoproliferative disease (XLP) is an inherited immune defect caused by mutations in the Src homology 2 domain-containing gene 1A, which encodes the adapter protein, signaling lymphocytic activation molecule (SLAM)-associated protein (SAP). SAP is expressed in T cells, natural killer (NK) cells, and NKT cells, where it binds to the cytoplasmic domain of the surface receptor SLAM (CD150) and the related receptors, 2B4 (CD244), CD84, Ly9 (CD229), NK-T-B-antigen, and CD2-like receptor-activating cytotoxic T cells. SAP also binds to the Src family tyrosine kinase Fyn and recruits it to SLAM, which leads to the generation of downstream phosphotyrosine signals. While the roles of the SLAM family receptors are only beginning to be understood, experiments suggest that these molecules regulate important aspects of lymphocyte function, such as proliferation, cytokine secretion, cytotoxicity, and antibody production. Thus, in XLP patients who lack functional SAP, the SLAM family receptors may not signal properly. This property likely contributes to the phenotypes of XLP, including fulminant infectious mononucleosis, lymphoma, and hypogammaglobulinemia. Further studies of SAP and the SLAM family receptors will provide insights into XLP and elucidate the signaling events regulating lymphocyte ontogeny and function. [ABSTRACT FROM AUTHOR]

Lymphocyte differentiation is a complex process regulated bythe integration of signals received through a variety of cell surfacereceptors that results in populations of differentiated cells thathave acquired novel characteristics and effector functions. Differentiationof T and B lymphocytes into effector cells, such as cytokine-secretingCD4+ T cells, cytotoxic CD8+ Tcells and Ig-secreting B cells, as well as alterations in cell surface phenotype,have been reported to be associated with cell division. Nevertheless,the genesis of heterogeneity in effector cell type is unknown. Astrictly deterministic view holds that heterogeneity arises fromdistinct signalling histories for each functionally or phenotypicallydifferent cell type. In contrast, a probabilistic interpretation proposesthat internal stochastic regulation of gene expression gives riseto lymphocytes of mixed phenotypes. To help distinguish betweenthese explanations, we examined the expression of CD27, CCR7, CD45RAand CD45RO by human naive CD4+ T cells in thecontext of the division history of the lymphocyte. Our results showthat each marker independently changes with progressive divisions,strongly supporting the proposal that phenotypic heterogeneity inlymphocytes can arise as the result of independent stochastic processescontrolling the expression of individual molecules. [ABSTRACT FROM AUTHOR]

The article presents a study on how the inflammatory cytokines through the induction of interleukin (IL)-21 modulates IL-9 production conducted by M.T. Wong and colleagues published within this issue. The differentiation of CD+ 4 T cells into Th9 cells can be induced by a combination of transforming growth factor (TGF)- ß and IL-4. The regulation of Th9 cells by other factors is investigated. The study suggests that Th9 cell differentiation can be negatively regulated by Th1 response.