Evolutionary implication of B-1 lineage cells from innate to adaptive immunity

Phagocytic Plasma Cells in Teleost Fish Provide Insights into the Origin and Evolution of B Cells in Vertebrates

Teleost IgM+ B cells can phagocytose, like mammalian B1 cells, and secrete Ag-specific IgM, like mammalian B2 cells. Therefore, teleost IgM+ B cells may have the functions of both mammalian B1 and B2 cells. To support this view, we initially found that grass carp (Ctenopharyngodon idella) IgM+ plasma cells (PCs) exhibit robust phagocytic ability, akin to IgM+ naive B cells. Subsequently, we sorted grass carp IgM+ PCs into two subpopulations: nonphagocytic (Pha-IgM+ PCs) and phagocytic IgM+ PCs (Pha+IgM+ PCs), both of which demonstrated the capacity to secrete natural IgM with LPS and peptidoglycan binding capacity. Remarkably, following immunization of grass carp with an Ag, we observed that both Pha-IgM+ PCs and Pha+IgM+ PCs could secrete Ag-specific IgM. Furthermore, in vitro concatenated phagocytosis experiments in which Pha-IgM+ PCs from an initial phagocytosis experiment were sorted and exposed again to beads confirmed that these cells also have phagocytic capabilities, thereby suggesting that all teleost IgM+ B cells have phagocytic potential. Additionally, we found that grass carp IgM+ PCs display classical phenotypic features of macrophages, providing support for the hypothesis that vertebrate B cells evolved from ancient phagocytes. These findings together reveal that teleost B cells are a primitive B cell type with functions reminiscent of both mammalian B1 and B2 cells, providing insights into the origin and evolution of B cells in vertebrates.

The Role of B1 Cells in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by multisystemic and multi-organ involvement, recurrent relapses and remissions, and the presence of large amounts of autoantibodies in the body as the main clinical features. The mechanisms involved in this disease are complex and remain poorly understood; however, they are generally believed to be related to genetic susceptibility factors, external stimulation of the body’s immune dysfunction, and impaired immune regulation. The main immune disorders include the imbalance of T lymphocyte subsets, hyperfunction of B cells, production of large amounts of autoantibodies, and further deposition of immune complexes, which result in tissue damage. Among these, B cells play a major role as antibody-producing cells and have been studied extensively. B1 cells are a group of important innate-like immune cells, which participate in various innate and autoimmune processes. Yet the role of B1 cells in SLE remains unclear. In this review, we focus on the mechanism of B1 cells in SLE to provide new directions to explore the pathogenesis and treatment modalities of SLE.

Analysis of phagocytosis by mIgM+ lymphocytes depending on monoclonal antibodies against IgM of largemouth bass (Micropterus salmoides)

The phagocytic actives of B cells in fish have been proven in recent years. In this study, five positive hybridomas secreting monoclonal antibodies (MAbs) against largemouth bass IgM were produced. Indirect immunofluorescence assay (IFA) demonstrated that five MAbs could specifically recognize membrane-bound IgM (mIgM) molecule of largemouth bass. Indirect ELISA and Western blotting analysis showed that all the five MAbs had no cross-reactions with the other two teleost IgMs. Flow cytometry analysis (FCM) revealed that the percentages of largemouth bass mIgM⁺ lymphocytes in head kidney, peripheral blood and spleen were 51.66 ± 0.608%, 16.5 ± 1.235% and 42.92 ± 1.091%, respectively. In addition, the phagocytosis rates of mIgM ⁺ lymphocytes ingesting Nocardia seriolae from head kidney, peripheral blood and spleen were calculated to be 5.413 ± 0.274%, 16.6 ± 0.289% and 26.3 ± 0.296%, respectively. The qPCR results of sorted cells indicated that most inflammatory cytokines (IFNγ, IL-1β, IL-2, IL-12β, IL-34, IL-10), chemokine (CXCL12), chemokines receptors (CXCR2, CXCR4) and genes (FcγRⅠa, NCF1, CFL, ARP2/3, CD45, Syk, MARCKS) related to FcγR-mediated phagocytic signaling pathway in phagocytic mIgM⁺ lymphocytes were up-regulated significantly (P < 0.05). Taken together, the results suggested that the MAb (MM06H) produced in this paper could be used as a tool to study mIgM⁺ lymphocytes of largemouth bass, and FcγR may participate in the phagocytosis of mIgM⁺ lymphocytes, which is helpful to further study the role of mIgM⁺ lymphocytes in innate immunity.

Contribution of classical complement activation and IgM to the control of Rickettsia infection

Pathogenic Rickettsia are obligate intracellular bacteria and the etiologic agents of many life‐threatening infectious diseases. Due to the serious nature of these infections, it is imperative to both identify the responsive immune sensory pathways and understand the associated immune mechanisms that restrict Rickettsia proliferation. Previous studies have demonstrated that the mammalian complement system is both activated during Rickettsia infection and contributes to the immune response to infection. To further define this component of the mammalian anti‐Rickettsia immune response, we sought to identify the mechanism(s) of complement activation during Rickettsia infection. We have employed a series of in vitro and in vivo models of infection to investigate the role of the classical complement activation pathway during Rickettsia infection. Depletion or elimination of complement activity demonstrates that both C1q and pre‐existing IgM contribute to complement activation; thus implicating the classical complement system in Rickettsia‐mediated complement activation. Elimination of the classical complement pathway from mice increases susceptibility to R. australis infection with both increased bacterial loads in multiple tissues and decreased immune activation markers. This study highlights the role of the classical complement pathway in immunity against Rickettsia and implicates resident Rickettsia‐responsive IgM in the response to infection.

Recent Advances on Phagocytic B Cells in Teleost Fish

The momentous discovery of phagocytic activity in teleost B cells has caused a dramatic paradigm shift from the belief that phagocytosis is performed mainly by professional phagocytes derived from common myeloid progenitor cells, such as macrophages/monocytes, neutrophils, and dendritic cells. Recent advances on phagocytic B cells and their microbicidal ability in teleost fish position B cells at the crossroads, bridging innate with adaptive immunity. Most importantly, an increasing body of experimental evidence demonstrates that, in both teleosts and mammals, phagocytic B cells can recognize, take up, and destroy particulate antigens and then present those processed antigens to CD4⁺ T cells to elicit adaptive immune responses and that the phagocytosis is mediated by pattern recognition receptors and involves multiple cytokines. Thus, current findings collectively indicate that teleost phagocytic B cells, as well as their counterpart mammalian B1-B cells, can be considered one kind of professional phagocyte. The aim of this review is to summarize recent advances regarding teleost phagocytic B cells, with a particular focus on the recognizing receptors and modulating mechanisms of phagocytic B cells and the process of antigen presentation for T-cell activation. We also attempt to provide new insights into the adaptive evolution of the teleost fish phagocytic B cell on the basis of its innate and adaptive roles.

Drivers and regulators of humoral innate immune responses to infection and cancer

The complement cascade consists of cell bound and serum proteins acting together to protect the host from pathogens, remove cancerous cells and effectively links innate and adaptive immune responses. Despite its usefulness in microbial neutralization and clearance of cancerous cells, excessive complement activation causes an immune imbalance and tissue damage in the host. Hence, a series of complement regulatory proteins present at a higher concentration in blood plasma and on cell surfaces tightly regulate the cascade. The complement cascade can be initiated by B-1 B cell production of natural antibodies. Natural antibodies arise spontaneously without any known exogenous antigenic or microbial stimulus and protect against invading pathogens, clear apoptotic cells, provide tissue homeostasis, and modulate adaptive immune functions. Natural IgM antibodies recognize microbial and cancer antigens and serve as an activator of complement mediated lysis. This review will discuss advances in complement activation and regulation in bacterial and viral infections, and cancer. We will also explore the crosstalk of natural antibodies with bacterial populations and cancer.

Role of teleost B cells in viral immunity

Teleost fish possess all the necessary elements to mount an adaptive immune response. Despite this, the important physiological and structural differences between the mammalian and the teleost fish immune system, anticipate significant changes regarding how this response is coordinated and executed. B cells are key players in adaptive immune responses through the production of antibodies. However, recent studies performed in mammals and other species including fish point to many additional functions of B cells within both the adaptive and the innate immune system, in many occasions taking part in the crosstalk between these two arms of the immune response. Furthermore, it should be taken into account that fish B cells share many functional and phenotypical features with innate B cell populations from mammals, which will surely condition their response to antigens. Concerning viral infections, although most studies undertaken to date in fish have been focused on characterizing antibody production, some recent studies have demonstrated that fish B cells are able to interact with viruses at different levels. In this sense, in the current review, we have tried to provide an overview of what is currently known regarding the role of teleost B cells in antiviral immunity.

The Role of Macrophage/B-Cell Interactions in the Pathophysiology of B-Cell Lymphomas

Macrophages (MPs) are heterogeneous, multifunctional, myeloid-derived leukocytes that are part of the innate immune system, playing wide-ranging critical roles in basic biological activities, including maintenance of tissue homeostasis involving clearance of microbial pathogens. Tumor-associated MPs (TAMs) are MPs with defined specific M2 phenotypes now known to play central roles in the pathophysiology of a wide spectrum of malignant neoplasms. Also, TAMs are often intrinsic cellular components of the essential tumor microenvironment (TME). In concert with lymphoid-lineage B and T cells at various developmental stages, TAMs can mediate enhanced tumor progression, often leading to poor clinical prognosis, at least partly through secretion of chemokines, cytokines, and various active proteases shown to stimulate tumor growth, angiogenesis, metastasis, and immunosuppression. Researchers recently showed that TAMs express certain key checkpoint-associated proteins [e.g., programmed cell death protein 1 (PD-1), programmed cell death-ligand 1 (PD-L1)] that appear to be involved in T-cell activation and that these proteins are targets of other specific checkpoint-blocking immunotherapies (anti-PD-1/PD-L1) currently part of new therapeutic paradigms for chemotherapy-resistant neoplasms. Although much is known about the wide spectrum and flexibility of MPs under many normal and neoplastic conditions, relatively little is known about the increasingly important interactions between MPs and B-lymphoid cells, particularly in the TME in patients with aggressive B-cell non-Hodgkin lymphoma (NHL-B). Normal and neoplastic lymphoid and myeloid cell/MP lineages appear to share many primitive cellular characteristics as well as transcriptional factor interactions in human and animal ontogenic studies. Such cells are capable of ectopic transcription factor-induced lineage reprogramming or transdifferentiation from early myeloid/monocytic lineages to later induce B-cell lymphomagenesis in experimental in vivo murine systems. Close cellular interactions between endogenous clonal neoplastic B cells and related aberrant myeloid precursor cells/MPs appear to be important interactive components of aggressive NHL-B that we discuss herein in the larger context of the putative role of B-cell/MP cellular lineage interactions involved in NHL-B pathophysiology during ensuing lymphoma development.

Assessment of leukocyte activity in mice devoid of the glucocorticoid receptor in the noradrenergic system (GRDBHCre)

Disturbances in brain monoamines, overactivity of the hypothalamo-pituitary adrenal (HPA) axis and pro-inflammatory tendency in the immune system are the key features of depressive disorders. Recently, several murine lines with mutations in glucocorticoid receptors (GRs) have been generated and these animals may be utilized for study depressive-like disorders. In the present study, we have investigated whether selective ablation of GRs in noradrenergic neurons affects functional properties of leukocytes and redirects them towards pro-inflammatory activity. Transgenic mice selectively devoid of GRs on noradrenergic cells were constructed using the Cre/loxP approach. Peritoneal leukocytes were collected from mutant and wild type (WT) animals of both sexes and were cultured in vitro for 24h both in basal conditions and after application of selected pro- or anti-inflammatory stimuli. Metabolic activity and adherence were measured in basal conditions. Nitric oxide (NO) synthesis and arginase (ARG) activity were assessed as the markers of functional status of the cells. Because adult mutant mice lack adrenal medulla and thereby peripheral adrenaline, we modulated pro- and anti-inflammatory culture conditions by addition of noradrenaline (10-6M). Finally, effects of in vivo pro-inflammatory challenge (with intraperitoneal administration of lipopolysaccharide) on properties of leukocytes were assessed 24h (in both sexes) and 48h later (in males only). The experiments indicated that selective ablation of GR in noradrenergic neurons did not affect fundamental properties of peritoneal leukocytes and exerted effects only under conditions of selected pro- or anti-inflammatory stimuli in vitro. Stronger response to pro-inflammatory stimulation in terms of NO synthesis and ARG activity may suggest pro-inflammatory tendency in mutant mice. In vivo inflammatory challenge failed to show any effect of GR ablation on selected parameters of leukocyte activity. Both in vitro studies and in vivo challenge revealed mainly sex-related differences in leukocyte activity.

Building conventions for unconventional lymphocytes

Falling between the classical characteristics of innate immune cells and adaptive T and B cells are a group of lymphocytes termed "unconventional." These cells express antigen-specific T or B cell receptors, but behave with innate characteristics. Well-known members of this group include the gamma-delta T cell and the Natural Killer T cell. Recent literature has greatly expanded scientific knowledge of unconventional lymphocytes, but key questions remain unresolved in the field, including why these cells have been maintained concurrently with conventional innate and adaptive immune cells. Here, we summarize current literature that suggests what their unique purposes may be, including specialized functions with the microbiota and in early development. From the consensus literature, we discuss where we see unconventional lymphocytes fit into the logical organization of the complete immune system.

Immunoglobulin (Ig)G1 and IgG4 anti-cyclic citrullinated peptide (CCP) associate with shared epitope, whereas IgG2 anti-CCP associates with smoking in patients with recent-onset rheumatoid arthritis (the Swedish TIRA project)

Given the possible importance of anti-citrullinated peptide/protein antibodies (ACPA) for initiation and progression of rheumatoid arthritis (RA), extended knowledge about the different isotypes and subclasses is important. In the present study, we analysed the immunoglobulin (Ig)G subclasses regarding reactivity against cyclic citrullinated peptides (anti-CCP) among 504 clinically well-characterized patients with recent-onset RA in relation to smoking habits, shared epitope (SE) status and IgA and pan-IgG anti-CCP antibodies. All patients, regardless of pan-IgG anti-CCP status, were analysed for IgG1-4 CCP reactivity. Sixty-nine per cent were positive in any IgG anti-CCP subclass, and of these 67% tested positive regarding IgG1, 35% IgG2, 32% IgG3, and 59% IgG4 anti-CCP. Among ever-smokers the percentages of IgG2 anti-CCP (P = 0·01) and IgA anti-CCP (P = 0·002)-positive cases were significantly higher compared to never-smokers. A positive IgG anti-CCP subclass -negative cases. Combining SE and smoking data revealed that IgG1 and IgG4 anti-CCP were the IgG anti-CCP isotypes associated with expression of SE, although the lower number of patients positive for IgG2 or IgG3 anti-CCP could, however, have influenced the results. High levels of IgG2 anti-CCP were shown to correlate with expression of the 'non-SE' allele human leucocyte antigen (HLA)-DRB1*15. In conclusion, in this study we describe different risk factor characteristics across the IgG anti-CCP subclasses, where IgG2 appears similar to IgA anti-CCP regarding the predominant association with smoking, while IgG1 and IgG4 related more distinctly to the carriage of SE genes.

Characterization of γδ T Cells from Zebrafish Provides Insights into Their Important Role in Adaptive Humoral Immunity

γδ T cells represent an evolutionarily primitive T cell subset characterized by distinct T cell receptors (TCRs) and innate and adaptive immune functions. However, the presence of this T cell subset in ancient vertebrates remains unclear. In this study, γδ T cells from a zebrafish (Danio rerio) model were subjected to molecular and cellular characterizations. The constant regions of zebrafish TCR-γ (DrTRGC) and δ (DrTRDC) were initially identified. Zebrafish γδ T cells accounted for 7.7–20.5% of the total lymphocytes in spleen, head kidney, peripheral blood, skin, gill, and intestine tissues. They possess typical morphological features of lymphocytes with a surface phenotype of γ⁺δ⁺CD4⁻CD8⁺. Zebrafish γδ T cells functionally showed a potent phagocytic ability to both soluble and particulate antigens. They can also act as an antigen-presenting cell to initiate antigen (KLH)-specific CD4⁺ T_KLH cell activation and to induce B cell proliferation and IgM production. Particularly, zebrafish γδ T cells also play a critical role in antigen-specific IgZ production in intestinal mucus. These findings demonstrated that γδ T cells had been originated as early as teleost fish, which providing valuable insights into the evolutionary history of T cell subset. It is anticipated that this study would be used as a guide to develop a zebrafish model for the cross-species investigation of γδ T cell biology.

TET1 and TET3 are essential in induction of Th2-type immunity partly through regulation of IL-4/13A expression in zebrafish model

It has been considered that epigenetic modulation can affect a diverse array of cellular activities, in which ten eleven translocation (TET) methylcytosine dioxygenase family members refer to a group of fundamental components involved in catalyzation of 5-hydroxymethylcytosine and modification of gene expression. Even though the function of TET proteins has been gradually revealed, their roles in immune regulation are still largely unknown. Recent studies provided clues that TET2 could regulate several innate immune-related inflammatory mediators in mammals. This study sought to explore the function of TET family members in potential T-helper (Th) cell differentiation involved in adaptive immunity by utilizing a zebrafish model. As shown by results, soluble antigens could induce expression of zebrafish IL-4/13A (i.e. a pivotal Th2-type cytokine essential in Th2 cell differentiation and functions), and further trigger the expression of Th1- and Th2-related genes. It is noteworthy that this response was accompanied by the up-regulation of two TET family members (TET1 and TET3) both in immune organs (spleen and kidney) and cells (peripheral lymphocytes). Knocking-down of TET1 and TET3 will give rise to the decreased responses of IL-4/13A induction against exogenous soluble antigen stimulation, and further restrain the expression of Th2-related genes, which indicates a restrained Th2 cell differentiation. Nonetheless, TET2 did not exhibit effect on the modification of Th1/Th2 related gene expression. Hence, these data showed that TET1 and TET3 might be two significant epigenetic regulators involved in Th2 differentiation through regulation of IL-4/13A expression. This is the first report to show that TET family members play indispensable roles in Th2-type immunity, indicating an epigenetic modulation manner involved in adaptive immune regulations and responses.

Novel Teleost CD4-Bearing Cell Populations Provide Insights into the Evolutionary Origins and Primordial Roles of CD4+ Lymphocytes and CD4+ Macrophages

Tetrapods contain a single CD4 coreceptor with four Ig domains that likely arose from a primordial two-domain ancestor. Notably, teleost fish contain two CD4 genes. Like tetrapod CD4, CD4-1 of rainbow trout includes four Ig domains, whereas CD4-2 contains only two. Because CD4-2 is reminiscent of the prototypic two-domain CD4 coreceptor, we hypothesized that by characterizing the cell types bearing CD4-1 and CD4-2, we would shed light into the evolution and primordial roles of CD4-bearing cells. Using newly established mAbs against CD4-1 and CD4-2, we identified two bona-fide CD4(+) T cell populations: a predominant lymphocyte population coexpressing surface CD4-1 and CD4-2 (CD4 double-positive [DP]), and a minor subset expressing only CD4-2 (CD4-2 single-positive [SP]). Although both subsets produced equivalent levels of Th1, Th17, and regulatory T cell cytokines upon bacterial infection, CD4-2 SP lymphocytes were less proliferative and displayed a more restricted TCRβ repertoire. These data suggest that CD4-2 SP cells represent a functionally distinct population and may embody a vestigial CD4(+) T cell subset, the roles of which reflect those of primeval CD4(+) T cells. Importantly, we also describe the first CD4(+) monocyte/macrophage population in a nonmammalian species. Of all myeloid subsets, we found the CD4(+) population to be the most phagocytic, whereas CD4(+) lymphocytes lacked this capacity. This study fills in an important gap in the knowledge of teleost CD4-bearing leukocytes, thus revealing critical insights into the evolutionary origins and primordial roles of CD4(+) lymphocytes and CD4(+) monocytes/macrophages.