Germinal center development

B cells and atherosclerosis: A HIV perspective

Atherosclerosis remains a leading cause of cardiovascular disease (CVD) globally, with the complex interplay of inflammation and lipid metabolism at its core. Recent evidence suggests a role of B cells in the pathogenesis of atherosclerosis; however, this relationship remains poorly understood, particularly in the context of HIV. We review the multifaceted functions of B cells in atherosclerosis, with a specific focus on HIV. Unique to atherosclerosis is the pivotal role of natural antibodies, particularly those targeting oxidized epitopes abundant in modified lipoproteins and cellular debris. B cells can exert control over cellular immune responses within atherosclerotic arteries through antigen presentation, chemokine production, cytokine production, and cell-cell interactions, actively participating in local and systemic immune responses. We explore how HIV, characterized by chronic immune activation and dysregulation, influences B cells in the context of atherosclerosis, potentially exacerbating CVD risk in persons with HIV. By examining the proatherogenic and antiatherogenic properties of B cells, we aim to deepen our understanding of how B cells influence atherosclerotic plaque development, especially within the framework of HIV. This research provides a foundation for novel B cell-targeted interventions, with the potential to mitigate inflammation-driven cardiovascular events, offering new perspectives on CVD risk management in PLWH.

Prognostication in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common type of leukemia in Western countries. CLL is a highly heterogeneous disease: some patients may never require therapy and others relapse several times after different therapeutic strategies. Therefore, in CLL, prognostic markers are essential to capture high-risk patients for different clinical endpoints including early treatment requirement, early progression after BTK or BCL2 inhibitors and Richter transformation. In early stage CLL, different biological and clinical biomarkers have been identified to predict time to treatment requirement that could be used to identify the most appropriate population for early intervention clinical trial. However, at the moment, the standard of care for early stage CLL remains watch & wait since no survival benefit has been identified in clinical trials with chemoimmunotherapy and with BTK inhibitors. In patients requiring treatment TP53 disruptions identify high-risk patients who benefit the most from long-term continuous therapy with BTKi. On the opposite side of the spectrum, IGHV mutated patients devoid of TP53 disruption benefit the most from fixed-duration therapy with venetoclax-obinutuzumab. In between, the highly heterogenous subgroup of patients with IGHV unmutated genes represents the group in which further efforts are needed to identify additional prognostic biomarkers aimed at selecting patients who can benefit from fixed-duration and patients who can benefit from long term BTKi therapy. In the context of the aggressive transformation of CLL, namely Richter syndrome, the clonal relationship to the CLL counterpart represents the strongest prognostic biomarker. Clonally related Richter syndrome still represents an unmet clinical need which requires further efforts to identify new therapeutic strategies.

Modeling the kinetics of lymph node retention and exposure of a cargo protein delivered by biotin-functionalized nanoparticles

Generation of protective immunity through vaccination arises from the adaptive immune response developed primarily in the lymph nodes drained from the immunization site. Relative to the intramuscular route, subcutaneous administration allows for direct and rapid access to the lymphatics, but accumulation of soluble protein antigens within the lymph nodes is limited. Subunit vaccines also require immune stimulating adjuvants which may not accumulate in the same lymph nodes simultaneously with antigen. Herein we report the use of biotinylated poly (lactic-co-glycolic acid) nanoparticles (bNPs) to enhance delivery of a model protein antigen to the lymphatics. bNPs provide dual functionality as adjuvant and vehicle to localize antigens with stimulated immune cells in the same draining lymph node. Using streptavidin as a model antigen, which can be loaded directly onto the bNP surface, we evaluated the kinetics of lymph node occupancy and adaptive immune responses in wildtype C57BL/6 mice. Antigen exposure in vivo was significantly improved through surface loading onto bNPs, and we developed a working kinetic model to account for the retention of both particles and antigen in draining lymph nodes. We observed enhanced T cell responses and antigen-specific B cell response in vivo when antigen was delivered on the particle surface. This work highlights the advantage of combining intrinsic adjuvant and antigen loading in a single entity, and the utility of kinetic modeling in the understanding of particle-based vaccines. STATEMENT OF SIGNIFICANCE: Development of safe and effective subunit vaccines depends on effective formulations that render optimized exposure and colocalization of antigens and adjuvants. In this work, we utilize a nanoparticle system which features self-adjuvanting properties and allows for surface loading of recombinant protein antigens. Using in vivo imaging, we demonstrated prolonged co-localization of the antigen and adjuvant particles in draining lymph nodes and provided evidence of B cell activation for up to 21 days following subcutaneous injection. A pharmacokinetic model was developed as a step towards bridging the translational gap between particulate-based vaccines and observed outcomes. The results have implications for the rational design of particle-based vaccines.

Prognostic Markers in the Era of Targeted Therapies

BACKGROUND

Small molecules targeting Bruton's tyrosine kinase (BTK) and B-cell lymphoma-2 have become the standard of care for the treatment of chronic lymphocytic leukemia (CLL), replacing chemoimmunotherapy (CIT) in most clinical settings. Ongoing trials explore targeted combinations and minimal residual disease-driven treatment cessation. These dramatic shifts in the current and upcoming treatment landscape of CLL raise the need to reevaluate existing prognostic markers and develop novel ones.

SUMMARY

This review examines prognostic markers in CLL patients treated with standard and investigational targeted therapies. Specifically, initial treatment of TP53 aberrant patients with a BTK inhibitor can achieve 70% progression-free survival (PFS) at 5 years, outperforming the 15% 5-year PFS with a CIT regimen containing fludarabine, cyclophosphamide, and rituximab (FCR). The prognostic implications of the immunoglobulin heavy chain variable gene (IGHV) mutation status have also changed. Unmutated IGHV is associated with inferior PFS and overall survival after FCR and inferior PFS with fixed-duration therapy with venetoclax and anti-CD20 monoclonal antibody but not with continuous BTK inhibitor treatment.

KEY MESSAGES

(1) Genetic variables (e.g., TP53 aberration, IGHV mutation, complex karyotype) have a prognostic significance in CLL patients treated with targeted therapy. (2) Understanding the prognostic and predictive values of these markers is critical for the development of a risk-adapted treatment strategy in CLL.

Selected Immunohistochemical Assessment and Clinical Examinations in the Diagnosis of Palatine Tonsil Diseases

INTRODUCTION

The palatine tonsils are secondary lymphoid organs where immune processes occur, influencing the development of a targeted cellular and humoral response. The diseased tonsils are subject to immunological imbalances, including the activity of pro-inflammatory and anti-inflammatory factors. This leads to the development of palatine tonsil diseases, such as palatine tonsillitis and palatine tonsillar hypertrophy.

AIM

The main aim of the study was to evaluate the similarities and differences in the clinical and pathomorphological pictures of patients qualified for surgical treatment due to hypertrophy or inflammation of the palatine tonsils. The aim was achieved by demonstrating the relationship between the patient's medical history and physical examination and histopathological diagnosis of a given tonsillar disease, evaluating the usefulness of basic blood tests (leukocytosis, ASO, ESR, and CRP) in differential diagnosis, and assessing the immunohistochemical assessment of palatine tonsil tissue.

MATERIAL AND METHODS

The tonsils were stained with the following antibodies: IL-1, IL-2, IL-6, IL-8 IL-10, and IL-37 and CD25, CD40, and CD69, taking into account the histological division of the studied lymphatic tissue (epithelial, subepithelial, follicular, follicular center, and interfollicular). Patients aged between 19 and 70 years with tonsillitis or clinical signs of tonsillar hypertrophy were qualified for tonsillectomy/UPPP. Seventy-two males (68.6%) and thirty-three females (31.4%) were enrolled in the study. Histopathological and immunohistochemical assessment was performed on 105 palatine tonsils.

RESULTS

The diagnostic value of blood tests, including determination of ASO, ESR, CRP, and leukocyte level, proved to be a significant predictor of tonsil disease. In the pathomorphological assessment, 75% of the subjects who had simultaneously elevated ESR (>4.73) and leukocytosis (>6.96) and reduced ASO (<161.03) and CRP (<0.31) belonged to the tonsillitis group. The immunohistochemical assessment revealed a diverse profile of the markers tested depending on the diagnosed disease of the tonsils. The follicular center proved to be the region of palatine tonsil tissue for which the most statistically significant differences between the markers were found. Responses to CD-40 and IL-1 were observed in this region. The tissue of epithelial, follicular, and interfollicular regions each showed one statistically significant value for the studied chemokines and lymphokines. However, the lack of significant statistical differences for p < 0.05 between the study groups was only noted in the subepithelial region. It should be emphasized that for the data as a whole (calculated on the basis of the data for all regions together), no statistically significant differences were observed.

CONCLUSION

In conclusion, the results obtained are indicative of the presence of a specific immunohistochemical profile for palatine tonsil diseases. Significant discrepancies have been found in the clinical and pathomorphological assessment of tonsils qualified for tonsillectomy. Therefore, these methods should be considered complementary. The patient's medical history and physical examination, depending on the adopted clinical or histopathological classification, show a variation in the distribution of features that are the basis for allocation to a particular group.

A Review of Compartmentalised Inflammation and Tertiary Lymphoid Structures in the Pathophysiology of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic, immune-mediated, demyelinating disease of the central nervous system (CNS). The most common form of MS is a relapsing–remitting disease characterised by acute episodes of demyelination associated with the breakdown of the blood–brain barrier (BBB). In the relapsing–remitting phase there is often relative recovery (remission) from relapses characterised clinically by complete or partial resolution of neurological symptoms. In the later and progressive stages of the disease process, accrual of neurological disability occurs in a pathological process independent of acute episodes of demyelination and is accompanied by a trapped or compartmentalised inflammatory response, most notable in the connective tissue spaces of the vasculature and leptomeninges occurring behind an intact BBB. This review focuses on compartmentalised inflammation in MS and in particular, what we know about meningeal tertiary lymphoid structures (TLS; also called B cell follicles) which are organised clusters of immune cells, associated with more severe and progressive forms of MS. Meningeal inflammation and TLS could represent an important fluid or imaging marker of disease activity, whose therapeutic abrogation might be necessary to stop the most severe outcomes of disease.

Platelets as Key Factors in Inflammation: Focus on CD40L/CD40

Platelets are anucleate cytoplasmic fragments derived from the fragmentation of medullary megakaryocytes. Activated platelets adhere to the damaged endothelium by means of glycoproteins on their surface, forming the platelet plug. Activated platelets can also secrete the contents of their granules, notably the growth factors contained in the α-granules, which are involved in platelet aggregation and maintain endothelial activation, but also contribute to vascular repair and angiogenesis. Platelets also have a major inflammatory and immune function in antibacterial defence, essentially through their Toll-like Receptors (TLRs) and Sialic acid-binding immunoglobulin-type lectin (SIGLEC). Platelet activation also contributes to the extensive release of anti- or pro-inflammatory mediators such as IL-1β, RANTES (Regulated on Activation, Normal T Expressed and Secreted) or CD154, also known as the CD40-ligand. Platelets are involved in the direct activation of immune cells, polynuclear neutrophils (PNNs) and dendritic cells via the CD40L/CD40 complex. As a general rule, all of the studies presented in this review show that platelets are capable of covering most of the stages of inflammation, primarily through the CD40L/CD40 interaction, thus confirming their own role in this pathophysiological condition.

System-Level Scenarios for the Elucidation of T Cell-Mediated Germinal Center B Cell Differentiation

Germinal center (GC) reactions are vital to the correct functioning of the adaptive immune system, through formation of high affinity, class switched antibodies. GCs are transient anatomical structures in secondary lymphoid organs where specific B cells, after recognition of antigen and with T cell help, undergo class switching. Subsequently, B cells cycle between zones of proliferation and somatic hypermutation and zones where renewed antigen acquisition and T cell help allows for selection of high affinity B cells (affinity maturation). Eventually GC B cells first differentiate into long-lived memory B cells (MBC) and finally into plasma cells (PC) that partially migrate to the bone marrow to encapsulate into long-lived survival niches. The regulation of GC reactions is a highly dynamically coordinated process that occurs between various cells and molecules that change in their signals. Here, we present a system-level perspective of T cell-mediated GC B cell differentiation, presenting and discussing the experimental and computational efforts on the regulation of the GCs. We aim to integrate Systems Biology with B cell biology, to advance elucidation of the regulation of high-affinity, class switched antibody formation, thus to shed light on the delicate functioning of the adaptive immune system. Specifically, we: i) review experimental findings of internal and external factors driving various GC dynamics, such as GC initiation, maturation and GCBC fate determination; ii) draw comparisons between experimental observations and mathematical modeling investigations; and iii) discuss and reflect on current strategies of modeling efforts, to elucidate B cell behavior during the GC tract. Finally, perspectives are specifically given on to the areas where a Systems Biology approach may be useful to predict novel GCBC-T cell interaction dynamics.

Isolation of primary human B lymphocytes from tonsils compared to blood as alternative source for ex vivo application

B lymphocytes ('B cells') are components of the human immune system with obvious potential for medical and biotechnological applications. Here, we discuss the isolation of primary human B cells from both juvenile and adult tonsillar material using a two-step procedure based on gradient centrifugation followed by separation on a nylon wool column as alternative to the current gold standard, i.e., negative immunosorting from buffy coats by antibody-coated magnetic beads. We show that the nylon wool separation is a low-cost method well suited to the isolation of large amounts of primary B cells reaching purities ≥ 80%. More importantly, this method allows the preservation of all B cell subsets, while MACS sorting seems to be biased against a certain B cell subtype, namely the CD27⁺ B cells. Importantly, compared to blood, the excellent recovery yield during purification of tonsillar B cells provides high number of cells, hence increases the number of subsequent experiments feasible with identical cell material, consequently improving comparability of results. The cultivability of the isolated B cells was demonstrated using pokeweed mitogen (PWM) as a stimulatory substance. Our results showed for the first time that the proliferative response of tonsillar B cells to mitogens declines with the age of the donor. Furthermore, we observed that PWM treatment stimulates the proliferation of a dedicated subpopulation and induces some terminal differentiation with ASCs signatures. Taken together this indicates that the proposed isolation procedure preserves the proliferative capability as well as the differentiation capacity of the B cells.

Epstein-Barr Virus DNA Exacerbates Colitis Symptoms in a Mouse Model of Inflammatory Bowel Disease

Infection with EBV has been associated with various inflammatory disorders including inflammatory bowel diseases (IBD). Contribution of this virus to intestinal disease processes has not been assessed. We previously detected that EBV DNA triggers proinflammatory responses via the activation of endosomal Toll-like receptor (TLR) signaling. Hence, to examine the colitogenic potential of EBV DNA, we used the dextran sodium sulfate (DSS) mouse colitis model. C57BL/6J mice received either DSS-containing or regular drinking water. Mice were then administered EBV DNA by rectal gavage. Administration of EBV DNA to the DSS-fed mice aggravated colonic disease activity as well as increased the damage to the colon histologic architecture. Moreover, we observed enhanced expression of IL-17A, IFNγ and TNFα in colon tissues from the colitis mice (DSS-treated) given the EBV DNA compared to the other groups. This group also had a marked decrease in expression of the CTLA4 immunoregulatory marker. On the other hand, we observed enhanced expression of endosomal TLRs in colon tissues from the EBV DNA-treated colitis mice. These findings indicate that EBV DNA exacerbates proinflammatory responses in colitis. The ubiquity of EBV in the population indicates that possible similar responses may be of pertinence in a relevant proportion of IBD patients.

Structure of the Eurasian moorhen spleen: A comprehensive study using gross anatomy, light, and transmission electron microscopy

The spleen is the largest secondary lymphoid organ with major roles in the removal of blood-borne antigens. The Eurasian moorhen is a wild aquatic bird that revealed the adaptation to harsh environmental conditions. Information regarding the structural features of moorhen's spleen is lacking. The present study aimed to describe the composition of moorhen's spleen using anatomical dissection, histology, histochemistry, immunohistochemistry, and transmission electron microscopy. The spleen appeared as a brownish red sickle-shaped organ close to the proventriculus and gizzard. The splenic capsule was very thin, and the trabeculae were poorly developed. The white pulp formed of the periarteriolar lymphoid sheath, lymphoid follicles, and periellipsoidal lymphatic sheath. The red pulp composed of sinusoids and cords and contained various types of blood cells. Blood vessels were observed within the splenic capsule and inside the parenchyma. Notably, penicillar capillaries (PCs) appeared branched and surrounded by well-developed ellipsoids. Direct connections were observed between PCs and splenic sinusoids suggesting a closed type of circulation. Ultrastructurally, intercellular spaces and vascular channels were evident in the wall of PCs. Ellipsoid-associated cells, lymphocytes, monocytes, and heterophils were observed within splenic ellipsoids. Ellipsoids were thus suggested as a crucial component of moorhen's spleen. Numerous MafB-immunoreactive (IR) macrophages were seen within the red pulp. Splenic cords contained the highest number of PHH3-IR cells, while CCASP3-IR cells were exclusive to follicles of the white pulp. In conclusion, the structure of moorhen's spleen revealed species-specific features. The findings of the present study could help to improve the immunity of domestic birds.

Accelerated Allograft Vasculopathy With Rituximab After Cardiac Transplantation

BACKGROUND

The CTOT-11 (Prevention of Cardiac Allograft Vasculopathy Using Rituximab Therapy in Cardiac Transplantation [Clinical Trials in Organ Transplantation-11]) study was a randomized, placebo-controlled, multicenter, double-blinded clinical trial in nonsensitized primary heart transplant (HTX) recipients.

OBJECTIVES

The study sought to determine whether B cell depletion therapy would attenuate the development of cardiac allograft vasculopathy.

METHODS

A total of 163 HTX recipients were randomized to rituximab 1,000 mg intravenous or placebo on days 0 and 12 post-transplant. Primary outcome was change in percent atheroma volume (PAV) from baseline to 1 year measured by intravascular ultrasound. Secondary outcomes included treated episodes of acute rejection, de novo anti-HLA antibodies (including donor-specific antibodies), and phenotypic differentiation of B cells.

RESULTS

There were no significant differences at study entry between the rituximab and placebo groups. Paired intravascular ultrasound measures were available at baseline and 1 year in 86 subjects (49 rituximab, 37 placebo). The mean ± SD change in PAV at 12 months was +6.8 ± 8.2% rituximab versus +1.9 ± 4.4% placebo (p = 0.0019). Mortality at 12 months was 3.4% rituximab versus 6.8% placebo (p = 0.47); there were no retransplants or post-transplant lymphoproliferative disorder. The rate of treated rejection was 24.7% rituximab versus 32.4% placebo (p = 0.28). Rituximab therapy effectively eliminated CD20⁺/CD19⁺ B cells followed by a gradual expansion of a CD19^- cell population in the rituximab-treated group.

CONCLUSIONS

A marked, unexpected increase in coronary artery PAV with rituximab was observed during the first year in HTX recipients. One-year mortality was not impacted; however, longer-term follow-up and mechanistic explanations are required. (Prevention of Cardiac Allograft Vasculopathy Using Rituximab [Rituxan] Therapy in Cardiac Transplantation; NCT01278745).

B cell reconstitution following alemtuzumab induction under a belatacept-based maintenance regimen

Lymphocyte depletion has been shown to control costimulation blockade-resistant rejection but, in some settings, to exacerbate antibody-mediated rejection (AMR). We have used alemtuzumab, which depletes T and B cells, combined with belatacept and rapamycin and previously reported control of both costimulation blockade-resistant rejection and AMR. To evaluate this regimen's effect on B cell signatures, we investigated 40 patients undergoing this therapy. B cell counts and phenotypes were interrogated using flow cytometry, and serum was analyzed for total IgG, IgM, and donor-specific alloantibody (DSA). Alemtuzumab induction produced pan-lymphocyte depletion; B cells repopulated faster and more completely than T cells. Reconstituting B cells were predominantly naïve, and memory B cells were significantly reduced (P = .001) post repopulation. Two B cell populations with potential immunomodulatory effects-regulatory (CD38^hi CD24^hi IgM^hi CD20^hi ) and transitional B cells (CD19⁺ CD27^- IgD⁺ CD38^hi )-were enriched posttransplant (P = .001). Total serum IgG decreased from baseline (P = .016) while IgM levels remained stable. Five patients developed DSAs within 36 months posttransplant, but none developed AMR. Baseline IgG levels in these patients were significantly higher than those in patients without DSAs. These findings suggest that belatacept and rapamycin together limit homeostatic B cell activation following B cell depletion and may lessen the risk of AMR. This regimen warrants prospective, comparative study. ClinicalTrials.gov NCT00565773.

2019 Russell Ross Memorial Lecture in Vascular Biology: B Lymphocyte-Mediated Protective Immunity in Atherosclerosis

Atherosclerosis-the major underlying pathology of cardiovascular disease-is characterized by accumulation and subsequent oxidative modification of lipoproteins within the artery wall, leading to inflammatory cell infiltration and lesion formation that can over time result in arterial stenosis, ischemia, and downstream adverse events. The contribution of innate and adaptive immunity to atherosclerosis development is well established, and B cells have emerged as important modulators of both pro- and anti-inflammatory effects in atherosclerosis. Murine B cells can broadly be divided into 2 subsets: (1) B-2 cells, which are bone marrow derived and include conventional follicular and marginal zone B cells, and (2) B-1 cells, which are largely fetal liver derived and persist in adults through self-renewal. B-cell subsets are developmentally, functionally, and phenotypically distinct with unique subset-specific contributions to atherosclerosis development. Mechanisms whereby B cells regulate vascular inflammation and atherosclerosis will be discussed with a particular emphasis on B-1 cells. B-1 cells have a protective role in atherosclerosis that is mediated in large part by IgM antibody production. Accumulating evidence over the last several years has pointed to a previously underappreciated heterogeneity in B-1 cell populations, which may have important implications for understanding atherosclerosis development and potential targeted therapeutic approaches. This heterogeneity within atheroprotective innate B-cell subsets will be highlighted.

B cell dysregulation in primary Sjögren's syndrome: A review

Primary Sjögren’s syndrome is a chronic autoimmune disorder of unknown etiology and is characterized by progressive focal lymphocytic infiltration of the lacrimal and salivary glands. Comparison of B cell subsets from the peripheral blood and salivary glands of patients with primary Sjögren’s syndrome and those from healthy individuals shows dysregulation and derangement of B cell subsets in both peripheral circulation and in inflamed glandular tissues. This dysregulation is expressed as a decrease in the percentage of CD27+ memory B cells in peripheral blood and an increase in the CD27+ memory B cells in the affected glands. Further, the overall percentage of long-lived autoantibodies-producing plasma cells within the affected glands is increased. In the last two decades, several studies have shown growing evidences that B cells play multiple roles in primary Sjögren’s syndrome pathophysiology, and that dysregulation of these cells may actually play a central role in the disease development.

Lack of Bcl-2 expression in feline follicular lymphomas

Bcl-2, an anti-apoptotic protein, is commonly overexpressed in follicular lymphomas in humans. This is usually the result of a chromosomal translocation that transposes the Bcl-2 gene into the immunoglobulin gene locus. The immunohistochemical assessment of this overexpression can be used as a tool for the differentiation of follicular lymphoma and follicular hyperplasia. In cats, little information about the expression of Bcl-2 in follicular lymphoma exists. We investigated 18 follicular lymphomas histologically and immunohistochemically for the expression of Bcl-2, CD3, CD45R, and feline leukemia virus. Clonality was assessed by PCR for antigen receptor gene rearrangements. Although the histology resembled that of their human counterparts, diffuse expression of Bcl-2 within the follicles of the feline lymphomas, as seen in human cases, was not present. Only single cells within the follicles, comparable to the reactive controls, were positive for Bcl-2 expression. The mean survival time of 4.6 y confirmed the indolent character of the tumor. None of the clinical parameters assessed were statistically significant predictors of survival. Furthermore, a statistically significant difference in survival of animals with or without anti-neoplastic therapy was also not demonstrable.

Remembrance of Things Past: Long-Term B Cell Memory After Infection and Vaccination

The success of vaccines is dependent on the generation and maintenance of immunological memory. The immune system can remember previously encountered pathogens, and memory B and T cells are critical in secondary responses to infection. Studies in mice have helped to understand how different memory B cell populations are generated following antigen exposure and how affinity for the antigen is determinant to B cell fate. Additionally, such studies were fundamental in defining memory B cell niches and how B cells respond following subsequent exposure with the same antigen. On the other hand, human studies are essential to the development of better, newer vaccines but sometimes limited by the difficulty to access primary and secondary lymphoid organs. However, work using human influenza and HIV virus infection and/or immunization in particular has significantly advanced today's understanding of memory B cells. This review will focus on the generation, function, and longevity of B-cell mediated immunological memory (memory B cells and plasma cells) in response to infection and vaccination both in mice and in humans.

Methods for Investigating VLA-4 (CD49d/CD29) Expression and Activation in Chronic Lymphocytic Leukemia and Its Clinical Applications

The integrin heterodimer CD49d/CD29 (a.k.a. Very Late Antigen-4, VLA-4) mediates cell-cell and cell-matrix interaction through the binding of its ligands VCAM-1 and fibronectin. VLA-4 can be present on the cell surface at different conformation states that affect the binding affinity for the ligands. In chronic lymphocytic leukemia (CLL), higher VLA-4 levels, as determined by measuring the expression of CD49d chain by flow cytometry, have been demonstrated to associate with a worse prognosis, in keeping with the role of VLA-4 as key molecule favoring CLL cell localization in protective niches of bone marrow and lymph nodes. Given the emerging clinical relevance of VLA-4 evaluation in CLL, both in the setting of the conventional chemo-immunotherapy and the novel drugs targeting the BCR pathway, here we describe the flow cytometric approaches followed by us to quantify the CD49d expression levels and the VLA-4 activation status in CLL cells.

Deficient for endoplasmic reticulum calcium sensors Stim1 and Stim2 affects aberrant antibody affinity maturation in B cells

Antigen specific B cells undergo a process termed affinity maturation in the germinal centers of secondary lymphoid organs where B cells with high affinity receptors are selected to mature into antibody-producing cells or to the memory B cell pool. It is known that B cell antigen receptor (BCR) signaling plays pivotal role in this selection process. Calcium influx is an essential component of BCR signaling. The current report is to determine the effect of calcium influx on antibody affinity maturation. In our studies, mice deficient for both endoplasmic reticulum calciumsensor Stim1 and Stim2 was immunized with T-cell dependent and independent antigens. Antibody affinity was measured by ELISA. We demonstrated that Stim1 &Stim2 deficient B cells exhibit accelerated pace of affinity maturation compared to wild type controls while the overall antibody production was not dramatically impaired to T-independent antigen immunization. In conclusion, calcium influx plays an important role in antibody affinity maturation in humoral immune responses. The knowledge can be used in manipulate humoral immune response for the design of effective vaccines.

Functional and clinical relevance of VLA-4 (CD49d/CD29) in ibrutinib-treated chronic lymphocytic leukemia

Tissino et al. demonstrate that in chronic lymphocytic leukemia, the VLA-4 (CD49d/CD29) integrin remains activable by B cell receptor stimulation also upon in vitro and in vivo ibrutinib exposure. Clinically, ibrutinib-treated CD49d-positive CLL patients experience reduced recirculation lymphocytosis and nodal response and inferior outcomes.

The Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib, which antagonizes B cell receptor (BCR) signals, demonstrates remarkable clinical activity in chronic lymphocytic leukemia (CLL). The lymphocytosis experienced by most patients under ibrutinib has previously been attributed to inhibition of BTK-dependent integrin and chemokine cues operating to retain the tumor cells in nodal compartments. Here, we show that the VLA-4 integrin, as expressed by CD49d-positive CLL, can be inside-out activated upon BCR triggering, thus reinforcing the adhesive capacities of CLL cells. In vitro and in vivo ibrutinib treatment, although reducing the constitutive VLA-4 activation and cell adhesion, can be overcome by exogenous BCR triggering in a BTK-independent manner involving PI3K. Clinically, in three independent ibrutinib-treated CLL cohorts, CD49d expression identifies cases with reduced lymphocytosis and inferior nodal response and behaves as independent predictor of shorter progression-free survival, suggesting the retention of CD49d-expressing CLL cells in tissue sites via activated VLA-4. Evaluation of CD49d expression should be incorporated in the characterization of CLL undergoing therapy with BCR inhibitors.

Isolation and characterization of an HIV-1 envelope glycoprotein-specific B-cell from an immortalized human naïve B-cell library

With the recent development of single B-cell cloning techniques, an increasing number of human immunodeficiency virus type 1 (HIV-1)-specific broadly neutralizing antibodies have been isolated since 2009. However, knowledge regarding HIV-1-specific B cells in vivo is limited. In this study, an HIV-1-specific B-cell line was established using healthy PBMC donors by the highly efficient Epstein-Barr virus transformation method to generate immortalized human naïve B-cell libraries. The enrichment of HIV-1 envelope-specific B cells was observed after four rounds of cell panning with the HIV-1 envelope glycoprotein. An HIV-1 envelope-specific stable B-cell line (LCL-P4) was generated. Although this cell line acquired a lymphoblastic phenotype, no expression was observed for activation-induced cytidine deaminase, an enzyme responsible for initiating somatic hypermutation and class switch recombination in B cells. This study describes a method that enables fast isolation of HIV-1-specific B cells, and this approach may extend to isolating other B-cell-specific antigens for further experiments.

Avidity of anti-malarial antibodies inversely related to transmission intensity at three sites in Uganda

Background

People living in malaria endemic areas acquire protection from severe malaria quickly, but protection from clinical disease and control of parasitaemia is acquired only after many years of repeated infections. Antibodies play a central role in protection from clinical disease; however, protective antibodies are slow to develop. This study sought to investigate the influence of Plasmodium falciparum exposure on the acquisition of high-avidity antibodies to P. falciparum antigens, which may be associated with protection.

Methods

Cross-sectional surveys were performed in children and adults at three sites in Uganda with varied P. falciparum transmission intensity (entomological inoculation rates; 3.8, 26.6, and 125 infectious bites per person per year). Sandwich ELISA was used to measure antibody responses to two P. falciparum merozoite surface antigens: merozoite surface protein 1-19 (MSP1-19) and apical membrane antigen 1 (AMA1). In individuals with detectable antibody levels, guanidine hydrochloride (GuHCl) was added to measure the relative avidity of antibody responses by ELISA.

Results

Within a site, there were no significant differences in median antibody levels between the three age groups. Between sites, median antibody levels were generally higher in the higher transmission sites, with differences more apparent for AMA-1 and in ≥5 year group. Similarly, median avidity index (proportion of high avidity antibodies) showed no significant increase with increasing age but was significantly lower at sites of higher transmission amongst participants ≥5 years of age. Using 5 M GuHCl, the median avidity indices in the ≥5 year group at the highest and lowest transmission sites were 19.9 and 26.8, respectively (p = 0.0002) for MSP1-19 and 12.2 and 17.2 (p = 0.0007) for AMA1.

Conclusion

Avidity to two different P. falciparum antigens was lower in areas of high transmission intensity compared to areas with lower transmission. Appreciation of the mechanisms behind these findings as well as their clinical consequences will require additional investigation, ideally utilizing longitudinal data and investigation of a broader array of responses.

Correlation of circulating CD27high plasma cells and disease activity in systemic lupus erythematosus

CD27 is a useful marker in assessing the number of circulating B cells and B cell subsets because it permits one step identification of the major B cell compartments, CD27- naïve and CD27+ memory B cells as well as CD27high plasma cells. Abnormalities in the distributionof CD27+ B cell subsets are useful in assessing disease activity in patients with systemic lupus erythematosus(SLE). In particular, the frequencyof CD27high plasma cells significantly correlates with lupus activity in both children and adults with SLE. Conventional immunosuppressive therapies affect the number of CD27- naive B cells and CD27high plasma cells, but do not target CD27+ memory B cells. These results suggest that disease flares may relate to the retention of CD27+ memory B cells after conventional immunosuppressive therapy and that new therapies that target these cells specifically may offer new opportunities to induce remission in SLE.

Effects of heat stress on the formation of splenic germinal centres and immunoglobulins in broilers infected by Clostridium perfringens type A

Avian necrotic enteritis (NE) induced by Clostridium perfringens is a disease that affects mainly the first weeks of poultry's life. The pathogenesis of NE is complex and involves the combination of several factors, such as co-infection with different species of coccidia, immunosuppression and stress. Stress is one of the main limiting factors in poultry production. Although several studies emphasized the effects of stress on immunity, few works analyzed these effects on immunoglobulins and on germinal centres (GCs), which are specialized microenvironments, responsible for generating immune cells with high affinity antibodies and memory B-lymphocytes. Thus, the effects of heat stress associated or not with thioglycolate broth culture medium intake and/or C. perfringens infection on corticosterone serum levels, spleen GCs development and immunoglobulin production in broilers were evaluated. Results showed that heat stress, thioglycolate and C. perfringens per se increased corticosterone serum levels, although this was not observed in heat stressed and thioglycolate and C. perfringens-treated chickens. The serum levels of IgA, IgM and IgY were differently affected by heat stress and/or infection/thioglycolate. Heat stress decreased the duodenal concentrations of sIgA, which was accompanied by a reduction in GCs number in the duodenal lamina propria; a trend to similar findings of sIgA concentrations was observed in the chickens' jejunum. Changes in spleen and Bursa of Fabricius relative weights as well as in spleen morphometry were also noted in heat stressed animals, infected or not. Together, these data suggest that heat stress change GCs formation in chickens infected or not, which that may lead to failures in vaccination protocols as well as in the poultries' host resistance to infectious diseases during periods of exposure to heat stress.

LLT1 and CD161 Expression in Human Germinal Centers Promotes B Cell Activation and CXCR4 Downregulation

Germinal centers (GCs) are microanatomical structures critical for the development of high-affinity Abs and B cell memory. They are organized into two zones, light and dark, with coordinated roles, controlled by local signaling. The innate lectin-like transcript 1 (LLT1) is known to be expressed on B cells, but its functional role in the GC reaction has not been explored. In this study, we report high expression of LLT1 on GC-associated B cells, early plasmablasts, and GC-derived lymphomas. LLT1 expression was readily induced via BCR, CD40, and CpG stimulation on B cells. Unexpectedly, we found high expression of the LLT1 ligand, CD161, on follicular dendritic cells. Triggering of LLT1 supported B cell activation, CD83 upregulation, and CXCR4 downregulation. Overall, these data suggest that LLT1–CD161 interactions play a novel and important role in B cell maturation within the GC in humans.

CD99 regulates CXCL12-induced chemotaxis of human plasma cells

Migration of plasma cells (PCs) is crucial for the control of PC survival and antibody production and is controlled by chemokines, most importantly by CXCL12. This study investigated the role of CD99 in CXCL12-induced PC migration. Among B cell subsets in the tonsils, CD99 expression was highest in PCs. CD99 expression increased during in vitro differentiation of germinal center B cells and was highest in PCs. CD99 engagement reduced chemotactic migration of PCs toward CXCL12 and reduced extracellular signal-regulated kinase (ERK) activation by CXCL12. An ERK inhibitor reduced CXCL12-mediated chemotactic migration, which suggests that ERK has a critical role in migration. CD99 engagement did not influence apoptosis, differentiation, or antibody secretion of PCs. We propose a novel role of CD99 in PCs that suppresses ERK activation and chemotactic migration of these cells.

IDO1 suppresses inhibitor development in hemophilia A treated with factor VIII

The development of inhibitory antibodies to factor VIII (FVIII) is a major obstacle in using this clotting factor to treat individuals with hemophilia A. Patients with a congenital absence of FVIII do not develop central tolerance to FVIII, and therefore, any control of their FVIII-reactive lymphocytes relies upon peripheral tolerance mechanisms. Indoleamine 2,3-dioxygenase 1 (IDO1) is a key regulatory enzyme that supports Treg function and peripheral tolerance in adult life. Here, we investigated the association between IDO1 competence and inhibitor status by evaluating hemophilia A patients harboring F8-null mutations that were either inhibitor negative (n = 50) or positive (n = 50). We analyzed IDO1 induction, expression, and function for any relationship with inhibitor occurrence by multivariable logistic regression and determined that defective TLR9-mediated activation of IDO1 induction is associated with an inhibitor-positive status. Evaluation of experimental hemophilic mouse models with or without functional IDO1 revealed that tryptophan metabolites, which result from IDO1 activity, prevent generation of anti-FVIII antibodies. Moreover, treatment of hemophilic animals with a TLR9 agonist suppressed FVIII-specific B cells by a mechanism that involves IDO1-dependent induction of Tregs. Together, these findings indicate that strategies aimed at improving IDO1 function should be further explored for preventing or eradicating inhibitors to therapeutically administered FVIII protein.

Calcineurin inhibitors dampen humoral immunity by acting directly on naive B cells

Calcineurin inhibitors (CNI), used frequently in solid organ transplant patients, are known to inhibit T cell proliferation, but their effect on humoral immunity is far less studied. Total and naive B cells from healthy adult donors were cultured in immunoglobulin (Ig)A- or IgG/IgE-promoting conditions with increasing doses of cyclosporin, tacrolimus, rapamycin or methylprednisolone. The effect on cell number, cell division, plasmablast differentiation and class-switching was tested. To examine the effect on T follicular helper (Tfh) cell differentiation, naive CD4(+) T cells were cultured with interleukin (IL)-12 and titrated immunosuppressive drug (IS) concentrations. Total B cell function was not affected by CNI. However, naive B cell proliferation was inhibited by cyclosporin and both CNI decreased plasmablast differentiation. Both CNI suppressed IgA, whereas only cyclosporin inhibited IgE class-switching. Rapamycin had a strong inhibitory effect on B cell function. Strikingly, methylprednisolone, increased plasmablast differentiation and IgE class-switching from naive B cells. Differentiation of Tfh cells decreased with increasing IS doses. CNI affected humoral immunity directly by suppressing naive B cells. CNI, as well as rapamycin and methylprednisolone, inhibited the in-vitro differentiation of Tfh from naive CD4(+) T cells. In view of its potent suppressive effect on B cell function and Tfh cell differentiation, rapamycin might be an interesting candidate in the management of B cell mediated complications post solid organ transplantation.

N-3 polyunsaturated fatty acids modulate B cell activity in pre-clinical models: Implications for the immune response to infections

B cell antigen presentation, cytokine production, and antibody production are targets of pharmacological intervention in inflammatory and infectious diseases. Here we review recent pre-clinical evidence demonstrating that pharmacologically relevant levels of n-3 polyunsaturated fatty acids (PUFA) derived from marine fish oils influence key aspects of B cell function through multiple mechanisms. N-3 PUFAs modestly diminish B cell mediated stimulation of classically defined naïve CD4(+) Th1 cells through the major histocompatibility complex (MHC) class II pathway. This is consistent with existing data showing that n-3 PUFAs suppress the activation of Th1/Th17 cells through direct effects on helper T cells and indirect effects on antigen presenting cells. Mechanistically, n-3 PUFAs lower antigen presentation and T cell signaling by disrupting the formation of lipid microdomains within the immunological synapse. We then review data to show that n-3 PUFAs boost B cell activation and antibody production in the absence and presence of antigen stimulation. This has potential benefits for several clinical populations such as the aged and obese that have poor humoral immunity. The mode of action by which n-3 PUFA boost B cell activation and antibody production remains unclear, but may involve Th2 cytokines, enhanced production of specialized proresolving lipid mediators, and targeting of protein lateral organization in lipid microdomains. Finally, we highlight evidence to show that different n-3 PUFAs are not biologically equivalent, which has implications for the development of future interventions to target B cell activity.

Circulating CXCR5+CD4+helper T cells in systemic lupus erythematosus patients share phenotypic properties with germinal center follicular helper T cells and promote antibody production

OBJECTIVE

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies. Recently, a specific highly activated T helper cell subset, follicular helper T (Tfh) cell, has emerged as a key immunoregulator of germinal center (GC) formation and high-affinity antibody production. To identify the pathophysiological role of Tfh cells in SLE patients, we compared the phenotypic and functional properties of circulating Tfh-like cells in lupus patients to GC-Tfh cells, and correlated the percentage of Tfh-like cells with autoantibody production and SLE disease activity.

METHODS

Peripheral blood was collected from 29 lupus patients and 25 healthy controls. Tonsils were obtained surgically from non-SLE controls and used as a source of GC-Tfh cells. Tfh cells were defined by their signature surface markers (CXCR5, ICOS, CD57, PD-1 and BTLA) via flow cytometry. IL-21 expression levels from Tfh cells were measured by real-time PCR and intracellular staining. The function of Tfh cells was carried out by co-culture of Tfh cells and autologous B cells in vitro. IgG in the culture supernatant was detected by ELISA.

RESULTS

The frequency of circulating Tfh-like cells was significantly increased in SLE patients compared to healthy controls (p < 0.05). The Tfh-like cells not only display similar phenotypes and signature cytokines with GC-Tfh cells, but also are capable of driving B cells to differentiate into IgG-secreting plasma cells in vitro. In addition, the frequency of Tfh-like cells correlated positively with the percentage of circulating plasmablasts, levels of serum anti-dsDNA antibodies and ANA.

CONCLUSION

The accumulated circulating Tfh-like cells in lupus patients share phenotypic and functional properties with GC-Tfh cells. Tfh-like cells may serve as perpetuators in the pathogenesis of SLE by enhancing the self-reactive B cell clones to further differentiate into auto antibody-producing plasmablasts, and ultimately cause autoimmunity.

Age-related differences in human palatine tonsillar B cell subsets and immunoglobulin isotypes

The tonsils provide defense of the upper aerodigestive tract against pathogens. Although long known to undergo functional changes with age, the precise changes occurring within tonsillar B cell populations remain undefined. In the present study, we investigated age-related changes in palatine tonsillar B cell subsets and immunoglobulin (Ig) isotypes. Palatine tonsils were obtained from forty-two tonsillectomy patients without tonsillitis who were divided into three groups: young children (4-9 years), adolescents (10-19 years), and adults (20-60 years). Tonsillar B cells were then analyzed by flow cytometry. Using expression of CD38 and IgD to define B cell subsets, we found that the frequency of germinal center (GC) B cells in the tonsils was significantly higher, and the frequency of memory B cells lower, in young children as compared to adolescents and adults. Within the GC B cell subsets, adults had a higher frequency of IgA(+) cells and a lower frequency of IgM(+) cells as compared to individuals in the younger age groups. Moreover, young children had a higher frequency of IgG(+) cells in the GC B cell subsets than did individuals in the older age groups. We also observed an abundance of IgM(+) cells among memory B cells and plasmablasts in young children and IgA(+) cells in adults. In summary, the proportion of GC B cells in palatine tonsillar B cells decreases with age, while the proportion of memory B cells increases with age. In addition, Ig isotypes in tonsils preferentially switch from IgM to IgA as individuals age.

EBV Persistence--Introducing the Virus

Persistent infection by EBV is explained by the germinal center model (GCM) which provides a satisfying and currently the only explanation for EBVs disparate biology. Since the GCM touches on every aspect of the virus, this chapter will serve as an introduction to the subsequent chapters. EBV is B lymphotropic, and its biology closely follows that of normal mature B lymphocytes. The virus persists quiescently in resting memory B cells for the lifetime of the host in a non-pathogenic state that is also invisible to the immune response. To access this compartment, the virus infects naïve B cells in the lymphoepithelium of the tonsils and activates these cells using the growth transcription program. These cells migrate to the GC where they switch to a more limited transcription program, the default program, which helps rescue them into the memory compartment where the virus persists. For egress, the infected memory cells return to the lymphoepithelium where they occasionally differentiate into plasma cells activating viral replication. The released virus can either infect more naïve B cells or be amplified in the epithelium for shedding. This cycle of infection and the quiescent state in memory B cells allow for lifetime persistence at a very low level that is remarkably stable over time. Mathematically, this is a stable fixed point where the mechanisms regulating persistence drive the state back to equilibrium when perturbed. This is the GCM of EBV persistence. Other possible sites and mechanisms of persistence will also be discussed.

C-type lectin-like receptor LOX-1 promotes dendritic cell-mediated class-switched B cell responses

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a pattern-recognition receptor for a variety of endogenous and exogenous ligands. However, LOX-1 function in the host immune response is not fully understood. Here, we report that LOX-1 expressed on dendritic cells (DCs) and B cells promotes humoral responses. On B cells LOX-1 signaling upregulated CCR7, promoting cellular migration toward lymphoid tissues. LOX-1 signaling on DCs licensed the cells to promote B cell differentiation into class-switched plasmablasts and led to downregulation of chemokine receptor CXCR5 and upregulation of chemokine receptor CCR10 on plasmablasts, enabling their exit from germinal centers and migration toward local mucosa and skin. Finally, we found that targeting influenza hemagglutinin 1 (HA1) subunit to LOX-1 elicited HA1-specific protective antibody responses in rhesus macaques. Thus, LOX-1 expressed on B cells and DC cells has complementary functions to promote humoral immune responses.

A multifactorial role for P. falciparum malaria in endemic Burkitt's lymphoma pathogenesis

Endemic Burkitt's lymphoma (eBL) arises from the germinal center (GC). It is a common tumor of young children in tropical Africa and its occurrence is closely linked geographically with the incidence of P. falciparum malaria. This association was noted more than 50 years ago. Since then we have learned that eBL contains the oncogenic herpes virus Epstein-Barr virus (EBV) and a defining translocation that activates the c-myc oncogene. However the link to malaria has never been explained. Here we provide evidence for a mechanism arising in the GC to explain this association. Accumulated evidence suggests that eBL arises in the GC when deregulated expression of AID (Activation-induced cytidine deaminase) causes a c-myc translocation in a cell latently infected with Epstein-Barr virus (EBV). Here we show that P. falciparum targets GC B cells via multiple pathways to increase the risk of eBL. 1. It causes deregulated expression of AID, thereby increasing the risk of a c-myc translocation. 2. It increases the number of B cells transiting the GC. 3. It dramatically increases the frequency of these cells that are infected with EBV and therefore protected from c-myc induced apoptosis. We propose that these activities combine synergistically to dramatically increase the incidence of eBL in individuals infected with malaria.

Endemic Burkitt's lymphoma (eBL) is a common tumor of young children in tropical Africa that is closely linked geographically with P. falciparum malaria. This association was noted more than 50 years ago. Since then we have learned that eBL contains the oncogenic herpes virus Epstein-Barr virus and a defining translocation that activates the c-myc oncogene. However the link to malaria has never been explained. Here we show that malaria has multiple effects that all focus on germinal center (GC) B cells that are known to be the origin of eBL. Together these effects of malaria act synergistically to dramatically increase the risk of developing eBL in individuals infected with the parasite. Clinical interventions that lessen the impact of malaria on GC B cells should dramatically decrease the incidence eBL.

Follicular B cells in thyroids of mice with spontaneous autoimmune thyroiditis contribute to disease pathogenesis and are targets of anti-CD20 antibody therapy

B cells are required for development of spontaneous autoimmune thyroiditis (SAT) in NOD.H-2h4 mice where they function as important APCs for activation of CD4(+) T cells. Depletion of B cells using anti-CD20 effectively inhibits SAT development. The goals of this study were to characterize the B cells that migrate to thyroids in SAT, and to determine whether anti-CD20 effectively targets those B cells in mice with established SAT. The results showed that most thyroid-infiltrating B cells in mice with SAT are follicular (FO) B cells. Expression of CD80, CD86, and CD40 was significantly increased on FO, but not marginal zone, splenic B cells after SAT development. Thyroid-infiltrating and peripheral blood B cells had lower expresion of CD20 and CD24 compared with splenic and lymph node FO B cells. Despite reduced CD20 expression, anti-CD20 depleted most B cells in thyroids of mice with established SAT within 3 d. B cell depletion in thyroids of mice given anti-CD20 was more complete and longer lasting than in spleen and lymph nodes and was comparable to that in blood. Circulation of B cells was required for effective and rapid removal of B cells in thyroids because preventing lymphocyte egress by administration of FTY720 abrogated the effects of anti-CD20 on thyroid B cells. Therefore, the FO subset of B cells preferentially contributes to SAT development and persistence, and anti-CD20 targeting of FO B cells effectively eliminates B cells in the target organ even though thyroid B cells have decreased CD20 expression.

Secretory IgA: Designed for Anti-Microbial Defense

Prevention of infections by vaccination remains a compelling goal to improve public health. Mucosal vaccines would make immunization procedures easier, be better suited for mass administration, and most efficiently induce immune exclusion - a term coined for non-inflammatory antibody shielding of internal body surfaces, mediated principally by secretory immunoglobulin A (SIgA). The exported antibodies are polymeric, mainly IgA dimers (pIgA), produced by local plasma cells (PCs) stimulated by antigens that target the mucose. SIgA was early shown to be complexed with an epithelial glycoprotein - the secretory component (SC). A common SC-dependent transport mechanism for pIgA and pentameric IgM was then proposed, implying that membrane SC acts as a receptor, now usually called the polymeric Ig receptor (pIgR). From the basolateral surface, pIg-pIgR complexes are taken up by endocytosis and then extruded into the lumen after apical cleavage of the receptor - bound SC having stabilizing and innate functions in the secretory antibodies. Mice deficient for pIgR show that this is the only receptor responsible for epithelial export of IgA and IgM. These knockout mice show a variety of defects in their mucosal defense and changes in their intestinal microbiota. In the gut, induction of B-cells occurs in gut-associated lymphoid tissue, particularly the Peyer's patches and isolated lymphoid follicles, but also in mesenteric lymph nodes. PC differentiation is accomplished in the lamina propria to which the activated memory/effector B-cells home. The airways also receive such cells from nasopharynx-associated lymphoid tissue but by different homing receptors. This compartmentalization is a challenge for mucosal vaccination, as are the mechanisms used by the mucosal immune system to discriminate between commensal symbionts (mutualism), pathobionts, and overt pathogens (elimination).

B-cell biology and development

B cells develop from hematopoietic precursor cells in an ordered maturation and selection process. Extensive studies with many different mouse mutants provided fundamental insights into this process. However, the characterization of genetic defects causing primary immunodeficiencies was essential in understanding human B-cell biology. Defects in pre-B-cell receptor components or in downstream signaling proteins, such as Bruton tyrosine kinase and B-cell linker protein, arrest development at the pre-B-cell stage. Defects in survival-regulating proteins, such as B-cell activator of the TNF-α family receptor (BAFF-R) or caspase recruitment domain-containing protein 11 (CARD11), interrupt maturation and prevent differentiation of transitional B cells into marginal zone and follicular B cells. Mature B-cell subsets, immune responses, and memory B-cell and plasma cell development are disturbed by mutations affecting Toll-like receptor signaling, B-cell antigen receptor coreceptors (eg, CD19), or enzymes responsible for immunoglobulin class-switch recombination. Transgenic mouse models helped to identify key regulatory mechanisms, such as receptor editing and clonal anergy, preventing the activation of B cells expressing antibodies recognizing autoantigens. Nevertheless, the combination of susceptible genetic backgrounds with the rescue of self-reactive B cells by T cells allows the generation of autoreactive clones found in patients with many autoimmune diseases and even in those with primary immunodeficiencies. The rapid progress of functional genomic research is expected to foster the development of new tools that specifically target dysfunctional B lymphocytes to treat autoimmunity, B-cell malignancies, and immunodeficiency.

TLR9-mediated signals rescue B-cells from Fas-induced apoptosis via inactivation of caspases

The death receptor, CD95/Fas, serves to eliminate potentially dangerous, self-reactive B cells. Engagement of B-cell receptors (BCR) on mature B-cells mediates the escape from cell death resulting in the activation and expansion of antigen specific clones. In addition to the antigen receptors, the receptors of B-cell activating factor belong to the tumor necrosis factor (TNF) family (BAFFR); moreover, the pattern recognition receptor, TLR9 may also deliver survival signals inhibiting Fas-mediated death of B-cells. Our aim was to compare the mechanism of BCR-induced and the BAFFR- or TLR9-stimulated rescue of B-cells from CD95/Fas-mediated apoptosis. We have found that BAFFR and TLR9 collaborate with BCR to protect B-cells from Fas-induced elimination and the rescue is independent of protein synthesis. The results revealed that the TLR9- and BCR-triggered rescue signals are transmitted through partially overlapping pathways; the protein kinase C (PKC) and the abl kinase induced phosphorylation may inactivate caspases in both CpG and anti-IgG stimulated cells. However, PI3-K activation is crucial upon the BCR driven anti-apoptotic effect, while p38 MAPK-mediated inactivation of caspases seems to play essential role in TLR9-mediated protection against Fas-induced programmed cell death.

The role of the tec kinase Bruton's tyrosine kinase (Btk) in leukocyte recruitment

Recruitment of leukocytes into inflamed tissue is a key component of the immune system. The activation of integrins on leukocytes is required for their recruitment into the inflamed tissue. Btk is a cytoplasmic nonreceptor tyrosine kinase belonging to the Tec-kinase family. It plays a key role in B-cell development and function, and recently published studies revealed important roles of Btk in myeloid cells. Btk might be activated through a variety of receptors leading to activation of integrins as the pivotal element in leukocyte recruitment. This review focuses on the role of Btk in B-lymphocyte homing and in neutrophil recruitment.

Transgenic overexpression of G5PR that is normally augmented in centrocytes impairs the enrichment of high-affinity antigen-specific B cells, increases peritoneal B-1a cells, and induces autoimmunity in aged female mice

To investigate signals that control B cell selection, we examined expression of G5PR, a regulatory subunit of the serine/threonine protein phosphatase 2A, which suppresses JNK phosphorylation. G5PR is upregulated in activated B cells, in Ki67-negative centrocytes at germinal centers (GCs), and in purified B220(+)Fas(+)GL7(+) mature GC B cells following Ag immunization. G5PR rescues transformed B cells from BCR-mediated activation-induced cell death by suppression of late-phase JNK activation. In G5PR-transgenic (G5PR(Tg)) mice, G5PR overexpression leads to an augmented generation of GC B cells via an increase in non-Ag-specific B cells and a consequent reduction in the proportion of Ag-specific B cells and high-affinity Ab production after immunization with nitrophenyl-conjugated chicken γ-globulin. G5PR overexpression impaired the affinity-maturation of Ag-specific B cells, presumably by diluting the numbers of high-affinity B cells. However, aged nonimmunized female G5PR(Tg) mice showed an increase in the numbers of peritoneal B-1a cells and the generation of autoantibodies. G5PR overexpression did not affect the proliferation of B-1a and B-2 cells but rescued B-1a cells from activation-induced cell death in vitro. G5PR might play a pivotal role in B cell selection not only for B-2 cells but also for B-1 cells in peripheral lymphoid organs.

Chemokine-dependent B cell-T cell interactions in chronic lymphocytic leukemia and multiple myeloma - targets for therapeutic intervention?

INTRODUCTION

Chemokines and their receptors play essential roles in the development, maintenance and proper functioning of the immune system. B cell-T cell interactions are modulated by chemokines. In B cell malignancies, these interactions may have tumor-promoting consequences.

AREAS COVERED

This review summarizes physiological B cell-T cell interactions and discusses their pathological role in the onset and progression of B cell malignancies with a special focus on chronic lymphocytic leukemia and multiple myeloma. Experimental data on chemokine-guided B cell-T cell actions in B cell malignancies from murine models as well as in vitro data are summarized and their potential as future therapeutic targets is critically discussed.

EXPERT OPINION

Direct or indirect targeting of chemokine receptors involved in localization and T-cell-dependent activation of B lymphocytes can provide strong synergisms with conventional or immunomodulatory therapies by disrupting the microenvironmental conditions necessary for survival and proliferation of malignant B lymphocytes. However, further knowledge of these interactions between B and T cells is needed.

GALT: organization and dynamics leading to IgA synthesis

Since its discovery more than four decades ago, immunoglobulin (Ig) A has been the subject of continuous and intensive studies. The major concepts derived were that the precursors of IgA plasma cells are generated in follicular organized structures with the help of T cells and the secreted IgAs provide protection against mucosal pathogens. However, only recently we began to appreciate that IgAs play key roles in regulation of bacterial communities in the intestine and that the repertoire of gut microbiota is closely linked to the proper functioning of the immune system. In this review, we highlight the complex and dynamic mutualistic relationships between bacteria and immune cells and discuss the sites and pathways leading to IgA synthesis in gut-associated lymphoid tissues (GALT).

Disrupted Mer receptor tyrosine kinase expression leads to enhanced MZ B-cell responses

Control of lymphocyte homeostasis is essential to ensure efficient immune responses and to prevent autoimmunity. Splenic marginal zone B cells are important producers of autoantibodies, and are subject to stringent tolerance mechanisms to prevent autoimmunity. In this paper, we explore the role of the Mer tyrosine kinase (Mertk) in regulating autoreactive B cells. This receptor tyrosine kinase serves to bind apoptotic cells, to mediate their phagocytosis, and to regulate subsequent cytokine production. Mice lacking Mertk suffer from impaired apoptotic cell clearance and develop a lupus-like autoimmune syndrome. Here we show that such Mertk-KO mice have expanded numbers of splenic marginal zone B cells. Mertk-KO mice bearing a DNA-specific immunoglobulin heavy-chain transgene (3H9) produced anti-DNA antibodies that appeared to be secreted largely by marginal zone B cells. Finally, Mertk-KO mice developed greater antibody responses after NP-Ficoll immunization than their B6 counterparts. Taken together, our data show that Mertk has a major effect on the development of the marginal zone B-cell compartment. Mertk is also important in establishing DNA-specific B-cell tolerance in 3H9 anti-DNA transgenic mice.

B Cell Abnormalities in Wegener’s Granulomatosis and Microscopic Polyangiitis: Role of CD25+-expressing B Cells

Objective.

The use of rituximab in vasculitis has increased interest in B cell biology. A subpopulation of B cells expressing CD25 shows antigen-presenting properties and may have regulatory functions. We assessed subpopulations of B cell maturation (Bm) and markers related to activity and antigen presentation, and related the findings to disease activity.

Methods.

Multiparameter flow cytometry was used to assess numbers and proportions of circulating lymphocytes from 34 patients with vasculitis (16 remission, 18 active) and 20 controls.

Results.

Active vasculitis samples showed decreased proportions of Bm1 (7.8% vs 11%; p = 0.041), Bm2’ (0.2% vs 0.7%; p = 0.002), and Bm3/Bm4 (0.1% vs 0.3%; p = 0.006), compared with controls; Bm2 cells were the most frequently occurring B cells but they were not significantly different in active vasculitis (74% vs 62%; p = 0.083). In patients with remission the proportion of CD25+ B cells was increased compared to controls (48% vs 29%, respectively; p = 0.006) and also compared to active vasculitis (23%; p = 0.006). The proportion of CD86+ B cells was also increased (31%) compared to active vasculitis (8%; p = 0.001), and to controls (6%; p = 0.0003). In multivariate analysis, Bm2’ cells and CD25+27– B cells were independently influencing the patient group.

Conclusion.

In active vasculitis, a lower proportion of Bm1 cells may indicate activated B cells. Patients in remission had higher proportions of CD25+ (α-chain of interleukin 2 receptor) and CD86+ (costimulatory molecule) B cells. We suggest that these B cells may have a regulatory role, or alternatively may result from previous treatment.