The rise and fall of long-lived humoral immunity: terminal differentiation of plasma cells in health and disease

Autoimmune Diseases and Plasma Cells Dyscrasias: Pathogenetic, Molecular and Prognostic Correlations

Multiple myeloma and monoclonal gammopathy of undetermined significance are plasma cell dyscrasias characterized by monoclonal proliferation of pathological plasma cells with uncontrolled production of immunoglobulins. Autoimmune pathologies are conditions in which T and B lymphocytes develop a tendency to activate towards self-antigens in the absence of exogenous triggers. The aim of our review is to show the possible correlations between the two pathological aspects. Molecular studies have shown how different cytokines that either cause inflammation or control the immune system play a part in the growth of immunotolerance conditions that make it easier for the development of neoplastic malignancies. Uncontrolled immune activation resulting in chronic inflammation is also known to be at the basis of the evolution toward neoplastic pathologies, as well as multiple myeloma. Another point is the impact that myeloma-specific therapies have on the course of concomitant autoimmune diseases. Indeed, cases have been observed of patients suffering from multiple myeloma treated with daratumumab and bortezomib who also benefited from their autoimmune condition or patients under treatment with immunomodulators in which there has been an arising or worsening of autoimmunity conditions. The role of bone marrow transplantation in the course of concomitant autoimmune diseases remains under analysis.

Investigation of the frequencies of various B cell populations in non-responder healthcare workers in comparison with responders to hepatitis B virus vaccination

BACKGROUND

Hepatitis B is a major global health problem. More than 90% of hepatitis B-vaccinated immunocompetent adults become fully immune. The main purpose of vaccination is immunization. Whether non-responders have a lower percentage of total or antigen-specific memory B cells in comparison with responders is still controversial. We aimed to assess and compare the frequency of various B cell subpopulations in non-responders and responders.

METHODS

Fourteen responders and 14 non-responders of hospital healthcare workers were enrolled in this study. We used flow cytometry to evaluate various CD19+ B cell subpopulations using fluorescent-labeled antibodies against CD19, CD10, CD21, CD27 and IgM and ELISA to evaluate total anti-HBs antibodies.

RESULTS

We found no significant differences in the frequency of various B cell subpopulations between the non-responder and responder groups. Furthermore, the frequency of the isotype-switched memory B cell population was significantly higher in the atypical memory B cell subset compared with the classical memory B cell subset in the responder and total groups (p=0.010 and 0.003, respectively).

CONCLUSIONS

Responders and non-responders to HBsAg vaccine had comparable memory B cell populations. Whether anti-HBs Ab production has a correlation with the level of class switching in B lymphocytes in healthy vaccinated individuals needs further investigation.

Inside-out assembly of viral antigens for the enhanced vaccination

Current attempts in vaccine delivery systems concentrate on replicating the natural dissemination of live pathogens, but neglect that pathogens evolve to evade the immune system rather than to provoke it. In the case of enveloped RNA viruses, it is the natural dissemination of nucleocapsid protein (NP, core antigen) and surface antigen that delays NP exposure to immune surveillance. Here, we report a multi-layered aluminum hydroxide-stabilized emulsion (MASE) to dictate the delivery sequence of the antigens. In this manner, the receptor-binding domain (RBD, surface antigen) of the spike protein was trapped inside the nanocavity, while NP was absorbed on the outside of the droplets, enabling the burst release of NP before RBD. Compared with the natural packaging strategy, the inside-out strategy induced potent type I interferon-mediated innate immune responses and triggered an immune-potentiated environment in advance, which subsequently boosted CD40⁺ DC activations and the engagement of the lymph nodes. In both H1N1 influenza and SARS-CoV-2 vaccines, rMASE significantly increased antigen-specific antibody secretion, memory T cell engagement, and Th1-biased immune response, which diminished viral loads after lethal challenge. By simply reversing the delivery sequence of the surface antigen and core antigen, the inside-out strategy may offer major implications for enhanced vaccinations against the enveloped RNA virus.

Selective emergence of antibody-secreting cells in the multiple sclerosis brain

BACKGROUND

Although distinct brain-homing B cells have been identified in multiple sclerosis (MS), it is unknown how these further evolve to contribute to local pathology. We explored B-cell maturation in the central nervous system (CNS) of MS patients and determined their association with immunoglobulin (Ig) production, T-cell presence, and lesion formation.

METHODS

Ex vivo flow cytometry was performed on post-mortem blood, cerebrospinal fluid (CSF), meninges and white matter from 28 MS and 10 control brain donors to characterize B cells and antibody-secreting cells (ASCs). MS brain tissue sections were analysed with immunostainings and microarrays. IgG index and CSF oligoclonal bands were measured with nephelometry, isoelectric focusing, and immunoblotting. Blood-derived B cells were cocultured under T follicular helper-like conditions to evaluate their ASC-differentiating capacity in vitro.

FINDINGS

ASC versus B-cell ratios were increased in post-mortem CNS compartments of MS but not control donors. Local presence of ASCs associated with a mature CD45^low phenotype, focal MS lesional activity, lesional Ig gene expression, and CSF IgG levels as well as clonality. In vitro B-cell maturation into ASCs did not differ between MS and control donors. Notably, lesional CD4⁺ memory T cells positively correlated with ASC presence, reflected by local interplay with T cells.

INTERPRETATION

These findings provide evidence that local B cells at least in late-stage MS preferentially mature into ASCs, which are largely responsible for intrathecal and local Ig production. This is especially seen in active MS white matter lesions and likely depends on the interaction with CD4⁺ memory T cells.

FUNDING

Stichting MS Research (19-1057 MS; 20-490f MS), National MS Fonds (OZ2018-003).

Autophagy and Its Lineage-Specific Roles in the Hematopoietic System

Autophagy is a dynamic process that regulates the selective and nonselective degradation of cytoplasmic components, such as damaged organelles and protein aggregates inside lysosomes to maintain tissue homeostasis. Different types of autophagy including macroautophagy, microautophagy, and chaperon-mediated autophagy (CMA) have been implicated in a variety of pathological conditions, such as cancer, aging, neurodegeneration, and developmental disorders. Furthermore, the molecular mechanism and biological functions of autophagy have been extensively studied in vertebrate hematopoiesis and human blood malignancies. In recent years, the hematopoietic lineage-specific roles of different autophagy-related (ATG) genes have gained more attention. The evolution of gene-editing technology and the easy access nature of hematopoietic stem cells (HSCs), hematopoietic progenitors, and precursor cells have facilitated the autophagy research to better understand how ATG genes function in the hematopoietic system. Taking advantage of the gene-editing platform, this review has summarized the roles of different ATGs at the hematopoietic cell level, their dysregulation, and pathological consequences throughout hematopoiesis.

Multi-epitope mRNA Vaccine Design that Exploits Variola Virus and Monkeypox Virus Proteins for Elicitation of Long-lasting Humoral and Cellular Protection Against Severe Disease

Human monkeypox represents a relatively underexplored infection that has received increased attention since the reported outbreak in May 2022. Due to its clinical similarities with human smallpox, this virus represents a potentially tremendous health problem demanding further research in the context of host-pathogen interactions and vaccine development. Furthermore, the cross-continental spread of monkeypox has reaffirmed the need for devoting attention to human poxviruses in general, as they represent potential bioterrorism agents. Currently, smallpox vaccines are utilized in immunization efforts against monkeypox, an unsurprising fact considering their genomic and phenotypic similarities. Though it offers long-lasting protection against smallpox, its protective effects against human monkeypox continue to be explored, with encouraging results. Taking this into account, this works aims at utilizing in silico tools to identify potent peptide-based epitopes stemming from the variola virus and monkeypox virus proteomes, to devise a vaccine that would offer significant protection against smallpox and monkeypox. In theory, a vaccine that offers cross-protection against variola and monkeypox would also protect against related viruses, at least in severe clinical manifestation. Herein, we introduce a novel multi-epitope mRNA vaccine design that exploits these two viral proteomes to elicit long-lasting humoral and cellular immunity. Special consideration was taken in ensuring that the vaccine candidate elicits a Th1 immune response, correlated with protection against clinically severe disease for both viruses. Immune system simulations and physicochemical and safety analyses characterize our vaccine candidate as antigenically potent, safe, and overall stable. The protein product displays high binding affinity towards relevant immune receptors. Furthermore, the vaccine candidate is to elicit a protective, humoral and Th1-dominated cellular immune response that lasts over five years. Lastly, we build a case about the rapidity and convenience of circumventing the live attenuated vaccine platform using mRNA vaccine technology.

An Update on Protective Effectiveness of Immune Responses After Recovery From COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exhibits variable immunity responses among hosts based on symptom severity. Whether immunity in recovered individuals is effective for avoiding reinfection is poorly understood. Determination of immune memory status against SARS-CoV-2 helps identify reinfection risk and vaccine efficacy. Hence, after recovery from COVID-19, evaluation of protective effectiveness and durable immunity of prior disease could be significant. Recent reports described the dynamics of SARS-CoV-2 -specific humoral and cellular responses for more than six months in convalescent SARS-CoV-2 individuals. Given the current evidence, NK cell subpopulations, especially the memory-like NK cell subset, indicate a significant role in determining COVID-19 severity. Still, the information on the long-term NK cell immunity conferred by SARS-CoV-2 infection is scant. The evidence from vaccine clinical trials and observational studies indicates that hybrid natural/vaccine immunity to SARS-CoV-2 seems to be notably potent protection. We suggested the combination of plasma therapy from recovered donors and vaccination could be effective. This focused review aims to update the current information regarding immune correlates of COVID-19 recovery to understand better the probability of reinfection in COVID-19 infected cases that may serve as guides for ongoing vaccine strategy improvement.

Overexpression of Interleukin-33 in Recombinant Rabies Virus Enhances Innate and Humoral Immune Responses through Activation of Dendritic Cell-Germinal Center Reactions

Rabies is a zoonotic infectious disease caused by rabies virus (RABV), and its mortality rate is as high as 100%. Globally, an average of 60,000 people die from rabies each year. The most effective method to prevent and limit rabies is vaccination, but it is currently expensive and inefficient, consisting of a 3-dose series of injections and requiring to be immunized annually. Therefore, it is urgent to develop a single dose of long-acting rabies vaccine. In this study, recombinant rabies virus (rRABV) overexpressing interleukin-33 (IL-33) was constructed and designated as rLBNSE-IL33, and its effect was evaluated in a mouse model. The results showed that rLBNSE-IL33 could enhance the quick production of RABV-induced immune antibodies as early as three days post immunization (dpi) through the activation of dendritic cells (DCs), a component of the innate immune system. Furthermore, rLBNSE-IL33 induced high-level virus-neutralizing antibodies (VNA) production that persisted for 8 weeks by regulating the T cell-dependent germinal center (GC) reaction, thus resulting in better protection against rabies. Our data suggest the IL-33 is a novel adjuvant that could be used to enhance innate and humoral immune responses by activating the DC-GC reaction, and thus, rLBNSE-IL33 could be developed as a safe and effective vaccine for animals.

Understanding the complexities of SARS-CoV2 infection and its immunology: A road to immune-based therapeutics

Emerging infectious diseases always pose a threat to humans along with plant and animal life. SARS-CoV2 is the recently emerged viral infection that originated from Wuhan city of the Republic of China in December 2019. Now, it has become a pandemic. Currently, SARS-CoV2 has infected more than 27.74 million people worldwide, and taken 901,928 human lives. It was named first 'WH 1 Human CoV' and later changed to 2019 novel CoV (2019-nCoV). Scientists have established it as a zoonotic viral disease emerged from Chinese horseshoe bats, which do not develop a severe infection. For example, Rhinolophus Chinese horseshoe bats harboring severe acute respiratory syndrome-related coronavirus (SARSr-CoV) or SARSr-Rh-BatCoV appear healthy and clear the virus within 2-4 months period. The article introduces first the concept of EIDs and some past EIDs, which have affected human life. Next section discusses mysteries regarding SARS-CoV2 origin, its evolution, and human transfer. Third section describes COVID-19 clinical symptoms and factors affecting susceptibility or resistance. The fourth section introduces the SARS-CoV2 entry in the host cell, its replication, and the establishment of productive infection. Section five describes the host's immune response associated with asymptomatic, symptomatic, mild to moderate, and severe COVID-19. The subsequent seventh and eighth sections mention the immune status in COVID-19 convalescent patients and re-emergence of COVID-19 in them. Thereafter, the eighth section describes viral strategies to hijack the host antiviral immune response and generate the "cytokine storm". The ninth section describes about transgenic humane ACE2 (hACE2) receptor expressing mice to study immunity, drugs, and vaccines. The article ends with the development of different immunomodulatory and immunotherapeutics strategies, including vaccines waiting for their approval in humans as prophylaxis or treatment measures.

Recombinant Rabies Virus Overexpressing OX40-Ligand Enhances Humoral Immune Responses by Increasing T Follicular Helper Cells and Germinal Center B Cells

Rabies, caused by the rabies virus (RABV), remains a serious threat to public health in most countries. Development of a single-dose and efficacious rabies vaccine is the most important method to restrict rabies virus transmission. Costimulatory factor OX40-ligand (OX40L) plays a crucial role in the T cell-dependent humoral immune responses through T-B cell interaction. In this work, a recombinant RABV overexpressing mouse OX40L (LBNSE-OX40L) was constructed, and its effects on immunogenicity were evaluated in a mouse model. LBNSE-OX40L-immunized mice generated a larger number of T follicular helper (Tfh) cells, germinal center (GC) B cells, and plasma cells (PCs) than the parent virus LBNSE-immunized mice. Furthermore, LBNSE-OX40L induced significantly higher levels of virus-neutralizing antibodies (VNA) as early as seven days post immunization (dpi), which lasted for eight weeks, resulting in better protection for mice than LBNSE (a live-attenuated rabies vaccine strain). Taken together, our data in this study suggest that OX40L can be a novel and potential adjuvant to improve the induction of protective antibody responses post RABV immunization by triggering T cell-dependent humoral immune responses, and that LBNSE-OX40L can be developed as an efficacious and nonpathogenic vaccine for animals.

Survival of Long-Lived Plasma Cells (LLPC): Piecing Together the Puzzle

Durable humoral immunity is dependent upon the generation of antigen-specific antibody titers, produced by non-proliferating bone marrow resident long-lived plasma cells (LLPC). Longevity is the hallmark of LLPC, but why and how they survive and function for years after antigen exposure is only beginning to be understood. LLPC are not intrinsically long-lived; they require continuous signals from the LLPC niche to survive. Signals unique to LLPC survival (vs. PC survival in general) most notably include those that upregulate the anti-apoptotic factor Mcl-1 and activation of the CD28 receptor expressed on LLPC. Other potential factors include expression of BCMA, upregulation of the transcription factor ZBTB20, and upregulation of the enzyme ENPP1. Metabolic fitness is another key component of LLPC longevity, facilitating the diversion of glucose to generate pyruvate during times of stress to facilitate long term survival. A third major component of LLPC survival is the microenvironment/LLPC niche itself. Cellular partners such as stromal cells, dendritic cells, and T regulatory cells establish a niche for LLPC and drive survival signaling by expressing ligands such as CD80/CD86 for CD28 and producing soluble and stromal factors that contribute to LLPC longevity. These findings have led to the current paradigm wherein both intrinsic and extrinsic mechanisms are required for the survival of LLPC. Here we outline this diverse network of signals and highlight the mechanisms thought to regulate and promote the survival of LLPC. Understanding this network of signals has direct implications in increasing our basic understanding of plasma cell biology, but also in vaccine and therapeutic drug development to address the pathologies that can arise from this subset.

Reversing Autoimmunity Combination of Rituximab and Intravenous Immunoglobulin

In this concept paper, the authors present a unique and novel protocol to treat autoimmune diseases that may have the potential to reverse autoimmunity. It uses a combination of B cell depletion therapy (BDT), specifically rituximab (RTX) and intravenous immunoglobulin (IVIg), based on a specifically designed protocol (Ahmed Protocol). Twelve infusions of RTX are given in 6–14 months. Once the CD20⁺ B cells are depleted from the peripheral blood, IVIg is given monthly until B cells repopulation occurs. Six additional cycles are given to end the protocol. During the stages of B cell depletion, repopulation and after clinical recovery, IVIg is continued. Along with clinical recovery, significant reduction and eventual disappearance of pathogenic autoantibody occurs. Administration of IVIg in the post-clinical period is a crucial part of this protocol. This combination reduces and may eventually significantly eliminates inflammation in the microenvironment and facilitates restoring immune balance. Consequently, the process of autoimmunity and the phenomenon that lead to autoimmune disease are arrested, and a sustained and prolonged disease and drug-free remission is achieved. Data from seven published studies, in which this combination protocol was used, are presented. It is known that BDT does not affect check points. IVIg has functions that mimic checkpoints. Hence, when inflammation is reduced and the microenvironment is favorable, IVIg may restore tolerance. The authors provide relevant information, molecular mechanism of action of BDT, IVIg, autoimmunity, and autoimmune diseases. The focus of the manuscript is providing an explanation, using the current literature, to demonstrate possible pathways, used by the combination of BDT and IVIg in providing sustained, long-term, drug-free remissions of autoimmune diseases, and thus reversing autoimmunity, albeit for the duration of the observation.

Bordetella bronchiseptica antigen enhances the production of Mycoplasma hyopneumoniae antigen-specific immunoglobulin G in mice

We previously demonstrated that Bordetella (B.) bronchiseptica antigen (Ag) showed high immunostimulatory effects on mouse bone marrow cells (BMs) while Mycoplasma (M.) hyopneumoniae Ag showed low effects. The focus of this study was to determine if B. bronchiseptica Ag can enhance the M. hyopneumoniae Ag-specific immune response and whether the host's immune system can recognize both Ags. MTT assay results revealed that each or both Ags did not significantly change BM metabolic activity. Flow cytometry analysis using carboxyfluorescein succinimidyl ester showed that B. bronchiseptica Ag can promote the division of BMs. In cytokine and nitric oxide (NO) assays, B. bronchiseptica Ag boosted production of tumor necrosis factor-alpha in M. hyopneumoniae Ag-treated BMs, and combined treatment with both Ags elevated the level of NO in BMs compared to that from treatment of M. hyopneumoniae Ag alone. Immunoglobulin (Ig)G enzyme-linked immunosorbent assay using the sera of Ag-injected mice clearly indicated that B. bronchiseptica Ag can increase the production of M. hyopneumoniae Ag-specific IgG. This study provided information valuable in the development of M. hyopneumoniae vaccines and showed that B. bronchiseptica Ag can be used both as a vaccine adjuvant and as a vaccine Ag.

Successful desensitization with proteasome inhibition and costimulation blockade in sensitized nonhuman primates

The detrimental effects of donor-directed antibodies in sensitized transplant patients remain a difficult immunologic barrier to successful organ transplantation. Antibody removal is often followed by rebound. Proteasome inhibitors (PIs) deplete antibody-producing plasma cells (PCs) but have shown marginal benefit for desensitization. In an allosensitized nonhuman primate (NHP) model, we observed increased germinal center (GC) formation after PI monotherapy, suggesting a compensatory PC repopulation mediated via GC activation. Here we show that costimulation blockade (CoB) targets GC follicular helper T (Tfh) cells in allosensitized NHPs. Combined PI and CoB significantly reduces bone marrow PCs (CD19⁺CD20^-CD38⁺), Tfh cells (CD4⁺ICOS⁺PD-1^hi), and GC B cells (BCL-6⁺CD20⁺); controls the homeostatic GC response to PC depletion; and sustains alloantibody decline. Importantly, dual PC and CoB therapy prolongs rejection-free graft survival in major histocompatibility complex incompatible kidney transplantation without alloantibody rebound. Our study illustrates a translatable desensitization method and provides mechanistic insight into maintenance of alloantibody sensitization.

Hypoxia favors the generation of human plasma cells

Plasma cells (PCs) generation occurs in hypoxic conditions in vivo, whereas the relevance of O₂ pressure in PC differentiation remains unknown. Using our in vitro PC differentiation model, we investigated the role of hypoxia in PC generation. Hypoxia increases the generation of plasmablasts (PBs) starting from memory B cells, by increasing cell cycle and division number. Reactome analysis demonstrated a significant enrichment of genes involved in HIF1α and HIF2α transcription factor network, metabolism and MYC related pathways in hypoxic compared with normoxic PBs. Hypoxia-induced metabolism alteration and MYC pathway are involved in malignant PC pathophysiology. Therefore, the expression of 28 out of the 74 genes overexpressed in hypoxic PBs compared with normoxic ones was found to be associated with an adverse prognosis (event free survival and overall survival) in newly diagnosed multiple myeloma patients. According to the role of hypoxia in supporting PBs generation through cell cycle induction, c-MYC activation and metabolism alteration, it could be involved in plasma cell tumorigenesis.

Overexpression of Interleukin-7 Extends the Humoral Immune Response Induced by Rabies Vaccination

Rabies continues to present a public health threat in most countries of the world. The most efficient way to prevent and control rabies is to implement vaccination programs for domestic animals. However, traditional inactivated vaccines used in animals are costly and have relatively low efficiency, which impedes their extensive use in developing countries. There is, therefore, an urgent need to develop single-dose and long-lasting rabies vaccines. However, little information is available regarding the mechanisms underlying immunological memory, which can broaden humoral responses following rabies vaccination. In this study, a recombinant rabies virus (RABV) that expressed murine interleukin-7 (IL-7), referred to here as rLBNSE-IL-7, was constructed, and its effectiveness was evaluated in a mouse model. rLBNSE-IL-7 induced higher rates of T follicular helper (Tfh) cells and germinal center (GC) B cells from draining lymph nodes (LNs) than the parent virus rLBNSE. Interestingly, rLBNSE-IL-7 improved the percentages of long-lived memory B cells (Bmem) in the draining LNs and plasma cells (PCs) in the bone marrow (BM) for up to 360 days postimmunization (dpi). As a result of the presence of the long-lived PCs, it also generated prolonged virus-neutralizing antibodies (VNAs), resulting in better protection against a lethal challenge than that seen with rLBNSE. Moreover, consistent with the increased numbers of Bmem and PCs after a boost with rLBNSE, rLBNSE-IL-7-immunized mice promptly produced a more potent secondary anti-RABV neutralizing antibody response than rLBNSE-immunized mice. Overall, our data suggest that overexpressing IL-7 improved the induction of long-lasting primary and secondary antibody responses post-RABV immunization.IMPORTANCE Extending humoral immune responses using adjuvants is an important method to develop long-lasting and efficient vaccines against rabies. However, little information is currently available regarding prolonged immunological memory post-RABV vaccination. In this study, a novel rabies vaccine that expressed murine IL-7 was developed. This vaccine enhanced the numbers of Tfh cells and the GC responses, resulting in upregulated quantities of Bmem and PCs. Moreover, we found that the long-lived PCs that were elicited by the IL-7-expressing recombinant virus (rLBNSE-IL-7) were able to sustain VNA levels much longer than those elicited by the parent rLBNSE virus. Upon reexposure to the pathogen, the longevous Bmem, which maintained higher numbers for up to 360 dpi with rLBNSE-IL-7 compared to rLBNSE, could differentiate into antibody-secreting cells, resulting in rapid and potent secondary production of VNAs. These results suggest that the expression of IL-7 is beneficial for induction of potent and long-lasting humoral immune responses.

Influence of Plasma Cell Niche Factors on the Recruitment and Maintenance of IRF4hi Plasma Cells and Plasmablasts in Vaccinated, Simian Immunodeficiency Virus-Infected Rhesus Macaques with Low and High Viremia

In a recent study, we found that protection following simian immunodeficiency virus (SIV) exposure correlated with rectal plasma cell frequency in vaccinated female rhesus macaques. We sought to determine if the same macaques maintained high mucosal plasma cell frequencies postinfection and if this translated to reduced viremia. Although delayed SIV acquisition did not predict subsequent viral control, alterations existed in the distribution of plasma cells and plasmablasts between macaques that exhibited high or low viremia. Flow cytometric analysis of cells from rectal biopsy specimens, bone marrow, and mesenteric lymph nodes of vaccinated infected, unvaccinated infected, and uninfected macaques identified two main IRF4^hi subsets of interest: CD138⁺ plasma cells, and CD138^- plasmablasts. In rectal tissue, plasma cell frequency positively correlated with plasma viremia and unvaccinated macaques had increased plasma cells and plasmablasts compared to vaccinated animals. Likewise, plasmablast frequency in the mesenteric lymph node correlated with viremia. However, in bone marrow, plasmablast frequency negatively correlated with viremia. Accordingly, low-viremic macaques had a higher frequency of both bone marrow IRF4^hi subsets than did animals with high viremia. Significant reciprocal relationships between rectal and bone marrow plasmablasts suggested that efficient trafficking to the bone marrow as opposed to the rectal mucosa was linked to viral control. mRNA expression analysis of proteins involved in establishment of plasma cell niches in sorted bone marrow and rectal cell populations further supported this model and revealed differential mRNA expression patterns in these tissues.

IMPORTANCE

As key antibody producers, plasma cells and plasmablasts are critical components of vaccine-induced immunity to human immunodeficiency virus type 1 (HIV-1) in humans and SIV in the macaque model; however, few have attempted to examine the role of these cells in viral suppression postinfection. Our results suggest that plasmablast trafficking to and retention in the bone marrow play a previously unappreciated role in viral control and contrast the potential contribution of mucosal plasma cells to mediate protection at sites of infection with that of bone marrow plasmablasts and plasma cells to control viremia during chronic infection. Manipulation of niche factors influencing the distribution and maintenance of these critical antibody-secreting cells may serve as potential therapeutic targets to enhance antiviral responses postvaccination and postinfection.

Staphylococcus aureus Protein A Disrupts Immunity Mediated by Long-Lived Plasma Cells

Infection with Staphylococcus aureus does not induce long-lived protective immunity for reasons that are not completely understood. Human and murine vaccine studies support a role for Abs in protecting against recurring infections, but S. aureus modulates the B cell response through expression of staphylococcus protein A (SpA), a surface protein that drives polyclonal B cell expansion and induces cell death in the absence of costimulation. In this murine study, we show that SpA altered the fate of plasmablasts and plasma cells (PCs) by enhancing the short-lived extrafollicular response and reducing the pool of bone marrow (BM)-resident long-lived PCs. The absence of long-lived PCs was associated with a rapid decline in Ag-specific class-switched Ab. In contrast, when previously inoculated mice were challenged with an isogenic SpA-deficient S. aureus mutant, cells proliferated in the BM survival niches and sustained long-term Ab titers. The effects of SpA on PC fate were limited to the secondary response, because Ab levels and the formation of B cell memory occurred normally during the primary response in mice inoculated with wild-type or SpA-deficient S. aureus mutant. Thus, failure to establish long-term protective Ab titers against S. aureus was not a consequence of diminished formation of B cell memory; instead, SpA reduced the proliferative capacity of PCs that entered the BM, diminishing the number of cells in the long-lived pool.

Small Molecule Inhibition of Rab7 Impairs B Cell Class Switching and Plasma Cell Survival To Dampen the Autoantibody Response in Murine Lupus

IgG autoantibodies mediate pathology in systemic lupus patients and lupus-prone mice. In this study, we showed that the class-switched IgG autoantibody response in MRL/Fas^lpr/lpr and C57/Sle1Sle2Sle2 mice was blocked by the CID 1067700 compound, which specifically targeted Ras-related in brain 7 (Rab7), an endosome-localized small GTPase that was upregulated in activated human and mouse lupus B cells, leading to prevention of disease development and extension of lifespan. These were associated with decreased IgG-expressing B cells and plasma cells, but unchanged numbers and functions of myeloid cells and T cells. The Rab7 inhibitor suppressed T cell-dependent and T cell-independent Ab responses, but it did not affect T cell-mediated clearance of Chlamydia infection, consistent with a B cell-specific role of Rab7. Indeed, B cells and plasma cells were inherently sensitive to Rab7 gene knockout or Rab7 activity inhibition in class switching and survival, respectively, whereas proliferation/survival of B cells and generation of plasma cells were not affected. Impairment of NF-κB activation upon Rab7 inhibition, together with the rescue of B cell class switching and plasma cell survival by enforced NF-κB activation, indicated that Rab7 mediates these processes by promoting NF-κB activation, likely through signal transduction on intracellular membrane structures. Thus, a single Rab7-inhibiting small molecule can target two stages of B cell differentiation to dampen the pathogenic autoantibody response in lupus.

The specialized proresolving mediator 17-HDHA enhances the antibody-mediated immune response against influenza virus: a new class of adjuvant?

Influenza viruses remain a critical global health concern. More efficacious vaccines are needed to protect against influenza virus, yet few adjuvants are approved for routine use. Specialized proresolving mediators (SPMs) are powerful endogenous bioactive regulators of inflammation, with great clinical translational properties. In this study, we investigated the ability of the SPM 17-HDHA to enhance the adaptive immune response using an OVA immunization model and a preclinical influenza vaccination mouse model. Our findings revealed that mice immunized with OVA plus 17-HDHA or with H1N1-derived HA protein plus 17-HDHA increased Ag-specific Ab titers. 17-HDHA increased the number of Ab-secreting cells in vitro and the number of HA-specific Ab-secreting cells present in the bone marrow. Importantly, the 17-HDHA-mediated increased Ab production was more protective against live pH1N1 influenza infection in mice. To our knowledge, this is the first report on the biological effects of ω-3-derived SPMs on the humoral immune response. These findings illustrate a previously unknown biological link between proresolution signals and the adaptive immune system. Furthermore, this work has important implications for the understanding of B cell biology, as well as the development of new potential vaccine adjuvants.

Lack of association between CD40 polymorphisms and acute rejection in German liver transplant recipients

CD40 and its ligand, CD154, are major costimulatory molecules whose interactions are important in alloreactive transplant rejection. The aim of this study was to examine the association of CD40 polymorphisms with the susceptibility to acute rejection episodes in liver transplantation. In total, 112 liver transplant recipients with biopsy proven acute rejections (BPAR), 97 without BPAR (WBPAR), and 112 healthy control individuals were enrolled in the study. Two single nucleotide polymorphisms (SNPs) of CD40 gene (rs1883832 and rs4810485) were genotyped by polymerase chain reaction-allele specific restriction enzyme analysis (PCR-ASRA). Both SNPs has been tested for a recessive and a dominant model. No significant differences were found in the genotype and allele frequencies of the SNPs rs1883832 and rs4810485 between BPAR liver recipients and WBPAR recipients. Our results do not suggest an important role of tested CD40 SNPs in the susceptibility to acute liver transplant rejection in a Caucasian population.

Long-lasting T cell-independent IgG responses require MyD88-mediated pathways and are maintained by high levels of virus persistence

Many viruses induce acute T cell-independent (TI) B cell responses due to their repetitive epitopes and the induction of innate cytokines. Nevertheless, T cell help is thought necessary for the development of long-lasting antiviral antibody responses in the form of long-lived plasma cells and memory B cells. We found that T cell-deficient (T cell receptor β and δ chain [TCRβδ] knockout [KO]) mice persistently infected with polyomavirus (PyV) had long-lasting antiviral serum IgG, and we questioned whether they could generate TI B cell memory. TCRβδ KO mice did not form germinal centers after PyV infection, lacked long-lived IgG-secreting plasma cells in bone marrow, and did not have detectable memory B cell responses. Mice deficient in CD4(+) T cells had a lower persisting virus load than TCRβδ KO mice, and these mice had short-lived antiviral IgG responses, suggesting that a high virus load is required to activate naive B cells continuously, and maintain the long-lasting serum IgG levels. Developing B cells in bone marrow encounter high levels of viral antigens, which can cross-link both their B cell receptor (BCR) and Toll-like receptors (TLRs), and this dual engagement may lead to a loss of their tolerance. Consistent with this hypothesis, antiviral serum IgG levels were greatly diminished in TCRβδ KO/MyD88(-/-) mice. We conclude that high persisting antigen levels and innate signaling can lead to the maintenance of long-lasting IgG responses even in the absence of T cell help.

IMPORTANCE

Lifelong control of persistent virus infections is essential for host survival. Several members of the polyomavirus family are prevalent in humans, persisting at low levels in most people without clinical manifestations, but causing rare morbidity/mortality in the severely immune compromised. Studying the multiple mechanisms that control viral persistence in a mouse model, we previously found that murine polyomavirus (PyV) induces protective T cell-independent (TI) antiviral IgG. TI antibody (Ab) responses are usually short-lived, but T cell-deficient PyV-infected mice can live for many months. This study investigates how protective IgG is maintained under these circumstances and shows that these mice lack both forms of B cell memory, but they still have sustained antiviral IgG responses if they have high levels of persisting virus and intact MyD88-mediated pathways. These requirements may ensure life-saving protection against pathogens even in the absence of T cells, but they prevent the continuous generation of TI IgG against harmless antigens.

IL-21 and CD40L synergistically promote plasma cell differentiation through upregulation of Blimp-1 in human B cells

After undergoing Ig somatic hypermutation and Ag selection, germinal center (GC) B cells terminally differentiate into either memory or plasma cells (PCs). It is known that the CD40L and IL-21/STAT3 signaling pathways play critical roles in this process, yet it is unclear how the B cell transcription program interprets and integrates these two types of T cell-derived signals. In this study, we characterized the role of STAT3 in the GC-associated PC differentiation using purified human tonsillar GC B cells and a GC B cell-like cell line. When primary GC B cells were cultured under PC differentiation condition, STAT3 inhibition by AG490 prevented the transition from GC centrocytes to preplasmablast, suggesting that STAT3 is required for the initiation of PC development. In a GC B cell-like human B cell line, although IL-21 alone can induce low-level Blimp-1 expression, maximum Blimp-1 upregulation and optimal PC differentiation required both IL-21 and CD40L. CD40L, although having no effect on Blimp-1 as a single agent, greatly augmented the amplitude and duration of IL-21-triggered Jak-STAT3 signaling. In the human PRDM1 locus, CD40L treatment enhanced the ability of STAT3 to upregulate Blimp-1 by removing BCL6, a potent inhibitor of Blimp-1 expression, from a shared BCL6/STAT3 site in intron 3. Thus, IL-21 and CD40L collaborate through at least two distinct mechanisms to synergistically promote Blimp-1 activation and PC differentiation.

A novel mouse model for multiple myeloma (MOPC315.BM) that allows noninvasive spatiotemporal detection of osteolytic disease

Multiple myeloma (MM) is a lethal human cancer characterized by a clonal expansion of malignant plasma cells in bone marrow. Mouse models of human MM are technically challenging and do not always recapitulate human disease. Therefore, new mouse models for MM are needed. Mineral-oil induced plasmacytomas (MOPC) develop in the peritoneal cavity of oil-injected BALB/c mice. However, MOPC typically grow extramedullary and are considered poor models of human MM. Here we describe an in vivo-selected MOPC315 variant, called MOPC315.BM, which can be maintained in vitro. When injected i.v. into BALB/c mice, MOPC315.BM cells exhibit tropism for bone marrow. As few as 10(4) MOPC315.BM cells injected i.v. induced paraplegia, a sign of spinal cord compression, in all mice within 3-4 weeks. MOPC315.BM cells were stably transfected with either firefly luciferase (MOPC315.BM.Luc) or DsRed (MOPC315.BM.DsRed) for studies using noninvasive imaging. MOPC315.BM.Luc cells were detected in the tibiofemoral region already 1 hour after i.v. injection. Bone foci developed progressively, and as of day 5, MM cells were detected in multiple sites in the axial skeleton. Additionally, the spleen (a hematopoietic organ in the mouse) was invariably affected. Luminescent signals correlated with serum myeloma protein concentration, allowing for easy tracking of tumor load with noninvasive imaging. Affected mice developed osteolytic lesions. The MOPC315.BM model employs a common strain of immunocompetent mice (BALB/c) and replicates many characteristics of human MM. The model should be suitable for studies of bone marrow tropism, development of osteolytic lesions, drug testing, and immunotherapy in MM.

Protective vaccine-induced CD4(+) T cell-independent B cell responses against rabies infection

A major goal in rabies virus (RV) research is to develop a single-dose postexposure prophylaxis (PEP) that would simplify vaccination protocols, reduce costs associated with rabies prevention in humans, and save lives. Live replication-deficient RV-based vaccines are emerging as promising single-dose vaccines to replace currently licensed inactivated RV-based vaccines. Nonetheless, little is known about how effective B cells develop in response to live RV-based vaccination. Understanding this fundamental property of rabies immunology may help in developing a single-dose RV vaccine. Typically, vaccines induce B cells secreting high-affinity, class-switched antibodies during germinal center (GC) reactions; however, there is a lag time between vaccination and the generation of GC B cells. In this report, we show that RV-specific antibodies are detected in mice immunized with live but not inactivated RV-based vaccines before B cells displaying a GC B cell phenotype (B220(+)GL7(hi)CD95(hi)) are formed, indicating a potential role for T cell-independent and early extrafollicular T cell-dependent antibody responses in the protection against RV infection. Using two mouse models of CD4(+) T cell deficiency, we show that B cells secreting virus-neutralizing antibodies (VNAs) are induced via T cell-independent mechanisms within 4 days postimmunization with a replication-deficient RV-based vaccine. Importantly, mice that are completely devoid of T cells (B6.129P2-Tcrβ(tm1Mom) Tcrδ(tm1Mom)/J) show protection against pathogenic challenge shortly after immunization with a live replication-deficient RV-based vaccine. We show that vaccines that can exploit early pathways of B cell activation and development may hold the key for the development of a single-dose RV vaccine wherein the rapid induction of VNA is critical.

CD4 costimulation is not required in a novel LPS-enhanced model of myasthenia gravis

The potential of lipopolysaccharide (LPS) to induce antigen-specific B cell responses to acetylcholine receptor (AChR) in myasthenia gravis (MG) was evaluated in wild type (WT) and CD4-/- C57BL/6 mice. The WT mice immunized with AChR in LPS developed an MG-like disease (LPS-EAMG) similar to that induced by immunization with AChR in complete Freund's adjuvant (CFA-EAMG). CD4-/- mice were resistant to CFA-EAMG but susceptible to LPS-EAMG. LPS abrogated EAMG resistance in CD4-/- mice by increasing high-affinity anti-AChR IgG2b in sera and enhancing immune complex deposition in muscle.

Molecular characteristics of mantle cell lymphoma presenting with clonal plasma cell component

The normal counterparts of mantle cell lymphoma (MCL) are naive, quiescent B cells that have not been processed through the germinal center (GC). For this reason, although lymphomas arising from GC or post-GC B cells often exhibit plasmacytic differentiation, MCL rarely presents with plasmacytic features. Seven cases of MCL with a monotypic plasma cell (PC) population were collected from 6 centers and were studied by immunohistochemistry, fluorescence immunophenotyping and interphase cytogenetics as a tool for the investigation of neoplasms analysis, capillary gel electrophoresis, and restriction fragment length polymorphism of immunoglobulin heavy chain analysis of microdissections of each of the MCL and PC populations to assess their clonal relationship. The clinical presentation was rather unusual compared with typical MCL, with 2 cases arising from the extranodal soft tissues of the head. All MCL cases were morphologically and immunohistochemically typical, bearing the t(11;14)(q13;q32). In all cases, the PC population was clonal. In 5 of the 7 cases, the MCL and PC clones showed identical restriction fragments, indicating a common clonal origin of the neoplastic population. The 2 cases with clonal diversity denoted the coexistence of 2 different tumors in a composite lymphoma/PC neoplasm. Our findings suggest that MCL can present with a PC component that is often clonally related to the lymphoma, representing a rare but unique biological variant of this tumor.

Recovery of B-cell homeostasis after rituximab in chronic graft-versus-host disease

Investigation of the effects of rituximab (anti-CD20) on B-cell-activating factor of the tumor necrosis factor family (BAFF) and B cells would better define the significance of B-cell homeostasis in chronic graft-versus-host disease (cGVHD) pathophysiology. We studied 20 cGVHD patients at a median of 25 months after rituximab treatment when most patients had recovered total B-cell numbers. A total of 55% of patients had stable/improved cGVHD, and total B-cell numbers in these patients were significantly higher compared with rituximab-unresponsive patients. Although total B-cell number did not differ significantly between cGVHD groups before rituximab, there was a proportional increase in B-cell precursors in patients who later had stable/improved cGVHD. After rituximab, BAFF levels increased in all patients. Coincident with B-cell recovery in the stable/improved group, BAFF/B-cell ratios and CD27(+) B-cell frequencies decreased significantly. The peripheral B-cell pool in stable/improved cGVHD patients was largely composed of naive IgD(+) B cells. By contrast, rituximab-unresponsive cGVHD patients had persistent elevation of BAFF and a predominance of circulating B cells possessing an activated BAFF-R(Lo)CD20(Lo) cell surface phenotype. Thus, naive B-cell reconstitution and decreased BAFF/B-cell ratios were associated with clinical response after rituximab in cGVHD. Our findings begin to delineate B-cell homeostatic mechanisms important for human immune tolerance.

The immortality of humoral immunity

Decades of high-titered antibody are sustained due to the persistence of memory B cells and long-lived plasma cells (PCs). The differentiation of each of these subsets is antigen- and T-cell driven and is dependent on signals acquired and integrated during the germinal center response. Inherent in the primary immune response must be the delivery of signals to B cells to create these populations, which have virtual immortality. Differences in biology and chemotactic behavior disperse memory B cells and long-lived PCs to a spectrum of anatomic sites. Each subset must rely on survival factors that can support their longevity. This review focuses on the generation of each of these subsets, their survival, and renewal, which must occur to sustain serological memory. In this context, we discuss the role of antigen, bystander inflammation, and cellular niches. The contribution of BAFF (B-cell activating factor belonging to the tumor necrosis factor family) and APRIL (a proliferation-inducing ligand) to the persistence of memory B cells and PCs are also detailed. Insights that have been provided over the past few years in the regulation of long-lived B-cell responses will have profound impact on vaccine development, the treatment of pre-sensitized patients for organ transplantation, and therapeutic interventions in both antibody- and T-cell-mediated autoimmunity.

Megakaryocytes constitute a functional component of a plasma cell niche in the bone marrow

Long-lived plasma cells in the bone marrow produce memory antibodies that provide immune protection persisting for decades after infection or vaccination but can also contribute to autoimmune and allergic diseases. However, the composition of the microenvironmental niches that are important for the generation and maintenance of these cells is only poorly understood. Here, we demonstrate that, within the bone marrow, plasma cells interact with the platelet precursors (megakaryocytes), which produce the prominent plasma cell survival factors APRIL (a proliferation-inducing ligand) and IL-6 (interleukin-6). Accordingly, reduced numbers of immature and mature plasma cells are found in the bone marrow of mice deficient for the thrombopoietin receptor (c-mpl) that show impaired megakaryopoiesis. After immunization, accumulation of antigen-specific plasma cells in the bone marrow is disturbed in these mice. Vice versa, injection of thrombopoietin allows the accumulation and persistence of a larger number of plasma cells generated in the course of a specific immune response in wild-type mice. These results demonstrate that megakaryocytes constitute an important component of the niche for long-lived plasma cells in the bone marrow.

Genetic immunization converts the trypanosoma cruzi B-Cell mitogen proline racemase to an effective immunogen

Trypanosoma cruzi is the etiologic agent of Chagas' disease. Acute T. cruzi infection results in polyclonal B-cell activation and delayed specific humoral immunity. T. cruzi proline racemase (TcPRAC), a T. cruzi B-cell mitogen, may contribute to this dysfunctional humoral response. Stimulation of murine splenocytes with recombinant protein (rTcPRAC) induced B-cell proliferation, antibody secretion, interleukin-10 (IL-10) production, and upregulation of CD69 and CD86 on B cells. Marginal zone (MZ) B cells are more responsive to T-cell-independent (TI) rTcPRAC stimulation than are follicular mature (FM) B cells in terms of proliferation, antibody secretion, and IL-10 production. During experimental T. cruzi infection, TcPRAC-specific IgG remained undetectable when responses to other T. cruzi antigens developed. Conversely, intradermal genetic immunization via gene gun (GG) delivered TcPRAC as an immunogen, generating high-titer TcPRAC-specific IgG without B-cell dysfunction. TcPRAC GG immunization led to antigen-specific splenic memory B-cell and bone marrow plasma cell formation. TcPRAC-specific IgG bound mitogenic rTcPRAC, decreasing subsequent B-cell activation. GG immunization with rTcPRAC DNA was nonmitogenic and did not affect the generation of specific IgG to another T. cruzi antigen, complement regulatory protein (CRP). These data demonstrate the utility of genetic immunization for the conversion of a protein mitogen to an effective antigen. Furthermore, coimmunization of TcPRAC with another T. cruzi antigen indicates the usefulness of this approach for multivalent vaccine development.

Transcription factors Xbp-1, Blimp-1, and BSAP are involved in the regulation of plasmacytic differentiation induced by 2-methoxyestradiol in myeloma cell lines

Our previous studies demonstrated that a low concentration of 2-methoxyestradiol (2ME2) could induce the differentiation of myeloma cell lines and CD138+ primary myeloma cells from myeloma patients and up-regulate the expression of messenger RNA (mRNA) and protein for the gene encoding X-box binding protein 1 (Xbp-1) in myeloma cell lines. In the present study, we used phosphorothioated antisense oligodeoxynucleotides (ASODN) to investigate the roles and interactions of transcription factors Xbp-1, B-lymphocyte induced maturation protein 1 (Blimp-1), and PAX-5-encoded B-cell-specific activator protein (BSAP), which are thought to be involved in the regulation of B-lymphocytic or plasmacytic differentiation. Blimp-1 ASODN and Xbp-1 ASODN clearly inhibited myeloma cell differentiation and significantly partially inhibited the differentiation effects induced by 2ME2 at low concentration, whereas PAX-5 ASODN clearly induced myeloma cell differentiation and significantly enhanced 2ME2-induced differentiation effects. Moreover, after incubation with Blimp-1 ASODN, the level of Xbp-1 mRNA clearly declined, whereas the level of PAX-5 mRNA significantly increased in myeloma cells. These results demonstrate that transcription factors Xbp-1, Blimp-1, and PAX-5-encoded BSAP play important roles in the regulation of plasmacytic differentiation and exert their effects on differentiation induced by low 2ME2 concentrations. Our primary study provided the rationale for a promising strategy-the future application of transcription-factor ASODN for clinical patients.

A functional TNFRSF5 gene variant is associated with risk of lymphoma

CD40 and its ligand, CD154, are major costimulatory molecules whose interactions are important in humoral and cellular immunity. We hypothesized that single nucleotide polymorphisms (SNPs) in TNFRSF5 and TNFSF5 encoding the CD40 and CD154 proteins, respectively, influence lymphoma risk, particularly a functional TNFRSF5 SNP (-1C>T, rs1883832) associated with reduced B-cell CD40 expression. TNFRSF5 and TNFSF5 SNPs were examined in a population-based case-control study of non-Hodgkin lymphoma (376 cases/801 controls with DNA), and compelling findings were followed up in 2 independent populations. Pooled analyses of all 3 case-control studies (total N = 1776 non-Hodgkin lymphoma cases, N = 2482 controls) revealed an increased risk of follicular lymphoma (FL) associated with the TNFRSF5 -1TT genotype (odds ratio = 1.6; 95% confidence interval, 1.1-2.4). In addition, among women, an inverse association was found between the variant A allele for a TNFSF5 6809G>A SNP and FL risk (OR = .61; 95% CI, 0.36-0.98). In genotype-phenotype studies, significantly reduced circulating soluble CD40 was observed in TNFRSF5 -1TT compared with -1CC carriers. Further, dendritic cells from those with -1TT versus -1CC genotypes exhibited lower CD40 cell surface expression. These results suggest that the TNFRSF5 -1C>T polymorphism may increase FL susceptibility through mechanisms that hinder cellular immune responses. Further studies are needed to explore these findings.

Duration of humoral immunity to common viral and vaccine antigens

BACKGROUND

Maintenance of long-term antibody responses is critical for protective immunity against many pathogens. However, the duration of humoral immunity and the role played by memory B cells remain poorly defined.

METHODS

We performed a longitudinal analysis of antibody titers specific for viral antigens (vaccinia, measles, mumps, rubella, varicella-zoster virus, and Epstein-Barr virus) and nonreplicating antigens (tetanus and diphtheria) in 45 subjects for a period of up to 26 years. In addition, we measured antigen-specific memory B cells by means of limiting-dilution analysis, and we compared memory B-cell frequencies to their corresponding serum antibody levels.

RESULTS

Antiviral antibody responses were remarkably stable, with half-lives ranging from an estimated 50 years for varicella-zoster virus to more than 200 years for other viruses such as measles and mumps. Antibody responses against tetanus and diphtheria antigens waned more quickly, with estimated half-lives of 11 years and 19 years, respectively. B-cell memory was long-lived, but there was no significant correlation between peripheral memory B-cell numbers and antibody levels for five of the eight antigens tested.

CONCLUSIONS

These studies provide quantitative analysis of serologic memory for multiple antigens in subjects followed longitudinally over the course of more than one decade. In cases in which multiple exposures or repeated vaccinations were common, memory B-cell numbers did not correlate with antibody titers. This finding suggests that peripheral memory B cells and antibody-secreting plasma cells may represent independently regulated cell populations and may play different roles in the maintenance of protective immunity.

Autoantibodies in patients with monoclonal gammopathies

Although autoantibody activities are rather often associated to monoclonal gammopathies, only monoclonal immunoglobulins of the IgM isotype are really directed against autoantigens that are often polysaccharides or are formed by highly repetitive structures. This strict association is frequently revealed also by clinical manifestations of the autoimmune response generated by the monoclonal macroglobulin. Most monoclonal immunoglobulins of non-IgM isotype are instead totally inactive toward self-antigens, the autoantibody activity being instead associated, if present, to polyclonal immunoglobulins. Although the same BAFF/APRIL system is involved in perpetuation of humoral autoimmunity as well as in stimulation of clonal B-cell expansion, the autoimmune commitment of B cells of a non-IgM isotype is hardly compatible with their possible involvement in an uncontrolled proliferation pathway, whose prerequisite is the homing of these B cells to the bone marrow compartment. The IgM-secreting cells appear instead to possess a much lower tendency, and/or a looser requirement, for their homing in the bone marrow prior to their actual proliferation. This may explain the quite different consequences, in terms of autoimmunity, between IgM and non-IgM paraproteinemias.

T cell-dependent survival of CD20+ and CD20- plasma cells in human secondary lymphoid tissue

The signals mediating human plasma cell survival in vivo, particularly within secondary lymphoid tissue, are unclear. Human tonsils grafted into immunodeficient mice were therefore used to delineate the mechanisms promoting the survival of plasma cells. Tonsillar plasma cells were maintained within the grafts and the majority were nonproliferating, indicating a long-lived phenotype. A significant depletion of graft plasma cells was observed after anti-CD20 treatment, consistent with the expression of CD20 by most of the cells. Moreover, anti-CD52 treatment caused the complete loss of all graft lymphocytes, including plasma cells. Unexpectedly, anti-CD3, but not anti-CD154, treatment caused the complete loss of plasma cells, indicating an essential role for T cells, but not CD40-CD154 interactions in plasma cell survival. The in vitro coculture of purified tonsillar plasma cells and T cells revealed a T-cell survival signal requiring cell contact. Furthermore, immunofluorescence studies detected a close association between human plasma cells and T cells in vivo. These data reveal that human tonsil contains long-lived plasma cells, the majority of which express CD20 and can be deleted with anti-CD20 therapy. In addition, an important role for contact-dependent interactions with T cells in human plasma cell survival within secondary lymphoid tissue was identified.

The kinetics and phenotype of the human B-cell response following immunization with a heptavalent pneumococcal-CRM conjugate vaccine

Primary immunization of infants with protein-polysaccharide conjugate vaccines induces antipolysaccharide antibody and is highly effective in preventing invasive disease caused by encapsulated bacteria. However, recent experience from the UK indicates that this immunity is not sustained in the absence of booster doses of vaccine. This study aimed to establish the kinetics and phenotype of B-cell subpopulations responding to booster immunization with a heptavalent pneumococcal conjugate vaccine (Pnc7), which is to be introduced into the primary immunization schedule in the UK during 2006. Six adult volunteers received a booster dose of Pnc7 12-18 months after primary immunization. CD27hi CD38hi CD20(+/-) IgG antibody-forming cells were detected in peripheral blood with maximum frequency at days 6-7 after immunization. This was accompanied by a more prolonged rise in memory B cells that required in vitro stimulation with Staphylococcus aureus Cowan strain and interleukin-2 to induce antibody secretion. These data provide evidence for at least two subsets of antibody-forming cells involved in the secondary humoral response to a glycoconjugate vaccine in primed individuals. A briefly circulating subset of B cells that spontaneously secrete immunoglobulin G may be responsible for early defence against re-encountered encapsulated bacteria. However, the kinetics of the appearance of these cells may indicate that the humoral immune response is too slow in defence against an organism that invades within days of acquisition. The more sustained presence of a memory population may provide persistence of antipolysaccharide antibody after a booster dose of vaccine and may also include re-circulatory populations responsible for further anamnestic responses.

Role of B Cells in Pathogenesis of Multiple Sclerosis

Despite the current limited understanding of the etiology of multiple sclerosis (MS), genetic susceptibility and environmental influences are known driving factors. MS is considered a T-cell-mediated disease given the prevalence of T cells in plaques. Plaque formation is characteristic of this disease attributable to immune mechanisms, triggered by an autoimmune attack aimed at antigens in the myelin sheath or oligodendrocyte proteins. The attack consists of the following: The role of the B cells is twofold: first, as autoreactive B cells they produce autoantibodies, secrete cytokines, clonally replicate memory B cells, and long-living plasma cells which serve to advance the diseased state by their constant production of autoantibodies. Second, as antigen-presenting cells they activate the autoreactive T cells. For this reason, the stipulation that T cell is the cornerstone of MS must be reevaluated. Various studies on pathogenesis of MS have indicated that B cells, as the humoral component of the adaptive immune system, are active participants in pathogenesis and lesion maintenance throughout the disease process. The active role of B cells and autoantibodies makes them an encouraging therapeutic target. Advances in the understanding of B-cell development and activity would allow for an enhanced strategy in the design of autoimmune treatment. For this reason, further investigation is necessary to determine whether depletion of B cells or antibodies may restore immune function.

Toll-like receptors mediate proliferation and survival of multiple myeloma cells

Multiple myeloma (MM) is an incurable B-cell malignancy characterized by accumulation of malignant plasma cells in bone marrow (BM) and recurrent or persistent infections. Toll-like receptors (TLRs) are essential in the host defense against infections and today 10 human TLRs (TLR1-TLR10) and one TLR-homolog (RP105) have been characterized. B cells express several TLRs (mainly TLR1, 6, 7, 9, 10 and RP105) and TLR-initiated responses in B cells include proliferation, anti-apoptosis effect and plasma cell (PC) differentiation. The present study was designed to analyze the role of TLRs in MM. We show that frequent expressions of TLRs were detected in cell lines from MM patients (minimum six TLRs in each). In comparison, only few TLRs (mainly TLR1 and or RP105) were found expressed in PCs from BM of healthy donors. In addition, TLR-specific ligands induce increased proliferation and survival of the MM cell lines, partially due to an autocrine interleukin-6 production. Importantly, we demonstrate that also PC from MM patients proliferates in response to TLR-specific ligands. In conclusion, TLR-ligands may contribute to increased growth and survival of MM cells in MM patients.

Treatment with rituximab affects both the cellular and the humoral arm of the immune system in patients with SLE

Herein we investigated how rituximab-induced B cell depletion affected leukocyte subpopulations and antibody titers in SLE patients. We focused our analysis on time points related to absence and return of B cells after depletion. A correlation was found between the baseline frequency and time to repopulation; the fewer B cells initially, the longer to their return. While the few B cells remaining after treatment were of memory, double-negative (IgD-CD27-), and CD5+ phenotype, the returning B cells were mainly naïve, indicating de novo production of B cells. Serum levels of IgG and antibodies against Ro52, Ro60, La44, measles and tetanus remained unchanged, while decreases in IgM, IgE, anti-dsDNA and anti-C1q antibodies were observed. Additionally, a significant increase in activated CD4+ and CD8+ T cells, as well as CD25bright FOXP3+ regulatory T cells was observed. In conclusion, both the humoral and the cellular immune systems were affected by treatment with rituximab.