Bone Marrow Antibody-secreting Cells Research Articles

Recruitment of plasma cells from IL-21-dependent and IL-21-independent immune reactions to the bone marrow

Bone marrow plasma cells (BMPC) are the correlate of humoral immunity, consistently releasing antibodies into the bloodstream. It remains unclear if BMPC reflect different activation environments or maturation of their precursors. Here we define human BMPC heterogeneity and track the recruitment of antibody-secreting cells (ASC) from SARS-CoV-2 vaccine immune reactions to the bone marrow (BM). Trajectories based on single-cell transcriptomes and repertoires of peripheral and BM ASC reveal sequential colonisation of BMPC compartments. In activated B cells, IL-21 suppresses CD19 expression, indicating that CD19low-BMPC are derived from follicular, while CD19high-BMPC originate from extrafollicular immune reactions. In primary immune reactions, both CD19low- and CD19high-BMPC compartments are populated. In secondary immune reactions, most BMPC are recruited to CD19high-BMPC compartments, reflecting their origin from extrafollicular reactivations of memory B cells. A pattern also observable in vaccinated-convalescent individuals and upon diphtheria/tetanus/pertussis recall-vaccination. Thus, BMPC diversity reflects the evolution of a given humoral immune response.

Proteasome inhibition reduces plasma cell and antibody secretion, but not angiotensin II-induced hypertension.

Depletion of mature B cells affords protection against experimental hypertension. However, whether B cell-mediated hypertension is dependent on differentiation into antibody-secreting cells (ASCs) remains unclear. Using the proteasome inhibitor, bortezomib, the present study tested the effect of ASC reduction on angiotensin II-induced hypertension. Male C57BL6/J mice were infused with angiotensin II (0.7 mg/kg/day; s.c.) for 28 days via osmotic minipump to induce hypertension. Normotensive control mice received saline infusion. Bortezomib (750 μg/kg) or vehicle (0.1% DMSO) was administered (i.v.) 3 days prior to minipump implantation, and twice weekly thereafter. Systolic blood pressure was measured weekly using tail-cuff plethysmography. Spleen and bone marrow B1 (CD19+B220-), B2 (B220+CD19+) and ASCs (CD138hiSca-1+Blimp-1+) were enumerated by flow cytometry. Serum immunoglobulins were quantified using a bead-based immunoassay. Bortezomib treatment reduced splenic ASCs by ∼68% and ∼64% compared to vehicle treatment in normotensive (2.00 ± 0.30 vs. 0.64 ± 0.15 × 105 cells; n = 10-11) and hypertensive mice (0.52 ± 0.11 vs. 0.14 ± 0.02 × 105 cells; n = 9-11), respectively. Bone marrow ASCs were also reduced by bortezomib in both normotensive (4.75 ± 1.53 vs. 1.71 ± 0.41 × 103 cells; n = 9-11) and hypertensive mice (4.12 ± 0.82 vs. 0.89 ± 0.18 × 103 cells; n = 9-11). Consistent with ASC reductions, bortezomib reduced serum IgM and IgG2a in all mice. Despite these reductions in ASCs and antibody levels, bortezomib did not affect angiotensin II-induced hypertension over 28 days (vehicle: 182 ± 4 mmHg vs. bortezomib: 177 ± 7 mmHg; n = 9-11). Reductions in ASCs and circulating IgG2a and IgM did not ameliorate experimental hypertension, suggesting other immunoglobulin isotypes or B cell effector functions may promote angiotensin II-induced hypertension.

CD39 and CD326 Are Bona Fide Markers of Murine and Human Plasma Cells and Identify a Bone Marrow Specific Plasma Cell Subpopulation in Lupus.

Antibody-secreting cells (ASCs) contribute to immunity through production of antibodies and cytokines. Identification of specific markers of ASC would allow selective targeting of these cells in several disease contexts. Here, we performed an unbiased, large-scale protein screening, and identified twelve new molecules that are specifically expressed by murine ASCs. Expression of these markers, particularly CD39, CD81, CD130, and CD326, is stable and offers an improved resolution for ASC identification. We accessed their expression in germ-free conditions and in T cell deficient mice, showing that at least in part their expression is controlled by microbial- and T cell-derived signals. Further analysis of lupus mice revealed the presence of a subpopulation of LAG-3– plasma cells, co-expressing high amounts of CD39 and CD326 in the bone marrow. This population was IgM+ and correlated with IgM anti-dsDNA autoantibodies in sera. Importantly, we found that CD39, CD81, CD130, and CD326 are also expressed by human peripheral blood and bone marrow ASCs. Our data provide innovative insights into ASC biology and function in mice and human, and identify an intriguing BM specific CD39++CD326++ ASC subpopulation in autoimmunity.

LT-K63 Enhances B Cell Activation and Survival Factors in Neonatal Mice That Translates Into Long-Lived Humoral Immunity.

Adjuvants enhance magnitude and duration of immune responses induced by vaccines. In this study we assessed in neonatal mice if and how the adjuvant LT-K63 given with a pneumococcal conjugate vaccine, Pnc1-TT, could affect the expression of tumor necrosis factor receptor (TNF-R) superfamily members, known to be involved in the initiation and maintenance of antibody responses; B cell activating factor receptor (BAFF-R) and B cell maturation antigen (BCMA) and their ligands, BAFF, and a proliferation inducing ligand (APRIL). Initially we assessed the maturation status of different B cell populations and their expression of BAFF-R and BCMA. Neonatal mice had dramatically fewer B cells than adult mice and the composition of different subsets within the B cell pool differed greatly. Proportionally newly formed B cells were most abundant, but they had diminished BAFF-R expression which could explain low proportions of marginal zone and follicular B cells observed. Limited BCMA expression was also detected in neonatal pre-plasmablasts/plasmablasts. LT-K63 enhanced vaccine-induced BAFF-R expression in splenic marginal zone, follicular and newly formed B cells, leading to increased plasmablast/plasma cells, and their enhanced expression of BCMA in spleen and bone marrow. Additionally, the induction of BAFF and APRIL expression occurred early in neonatal mice immunized with Pnc1-TT either with or without LT-K63. However, BAFF+ and APRIL+ cells in spleens were maintained at a higher level in mice that received the adjuvant. Furthermore, the early increase of APRIL+ cells in bone marrow was more profound in mice immunized with vaccine and adjuvant. Finally, we assessed, for the first time in neonatal mice, accessory cells of the plasma cell niche in bone marrow and their secretion of APRIL. We found that LT-K63 enhanced the frequency and APRIL expression of eosinophils, macrophages, and megakaryocytes, which likely contributed to plasma cell survival, even though APRIL+ cells showed a fast decline. All this was associated with enhanced, sustained vaccine-specific antibody-secreting cells in bone marrow and persisting vaccine-specific serum antibodies. Our study sheds light on the mechanisms behind the adjuvanticity of LT-K63 and identifies molecular pathways that should be triggered by vaccine adjuvants to induce sustained humoral immunity in early life.

Short Vi-polysaccharide abrogates T-independent immune response and hyporesponsiveness elicited by long Vi-CRM197 conjugate vaccine

Polysaccharide-protein conjugates have been developed to overcome the T-independent response, hyporesponsiveness to repeated vaccination, and poor immunogenicity in infants of polysaccharides. To address the impact of polysaccharide length, typhoid conjugates made with short- and long-chain fractions of Vi polysaccharide with average sizes of 9.5, 22.8, 42.7, 82.0, and 165 kDa were compared. Long-chain-conjugated Vi (165 kDa) induced a response in both wild-type and T cell-deficient mice, suggesting that it maintains a T-independent response. In marked contrast, short-chain Vi (9.5 to 42.7 kDa) conjugates induced a response in wild-type mice but not in T cell-deficient mice, suggesting that the response is dependent on T cell help. Mechanistically, this was explained in neonatal mice, in which long-chain, but not short-chain, Vi conjugate induced late apoptosis of Vi-specific B cells in spleen and early depletion of Vi-specific B cells in bone marrow, resulting in hyporesponsiveness and lack of long-term persistence of Vi-specific IgG in serum and IgG+ antibody-secreting cells in bone marrow. We conclude that while conjugation of long-chain Vi generates T-dependent antigens, the conjugates also retain T-independent properties, leading to detrimental effects on immune responses. The data reported here may explain some inconsistencies observed in clinical trials and help guide the design of effective conjugate vaccines.

CD19-positive antibody-secreting cells provide immune memory

AbstractLong-lived antibody-secreting cells (ASCs) are critical for the maintenance of humoral immunity through the continued production of antibodies specific for previously encountered pathogen or vaccine antigens. Recent reports describing humoral immune memory have suggested the importance of long-lived CD19− bone marrow (BM) ASCs, which secrete antibodies recognizing previously encountered vaccine antigens. However, these reports do not agree upon the unique contribution of the CD19+ BM ASC subset toward humoral immunity. Here, we found both CD19+ and negative ASCs from human BM were similar in functional capacity to react to a number of vaccine antigens via ELISpot assays. The CD19+ cells were the predominant ASC population found in lymphoid tissues, and unlike the CD19− ASCs, which were found only in spleen and BM, the CD19+ ASCs were found in tonsil and blood. CD19+ ASCs from the BM, spleen, and tonsil were capable of recognizing polio vaccine antigens, indicating the CD19+ ASC cells play a novel role in long-lasting immune defense. Comparative gene expression analysis indicated CD19+ and negative BM ASCs differed significantly by only 14 distinct messenger RNAs and exhibited similar gene expression for cell cycle, autophagy, and apoptosis control necessary for long life. In addition, we show identical CDR-H3 sequences found on both BM ASC subsets, indicating a shared developmental path. Together, these results provide novel insight for the distribution, function, genetic regulation, and development of long-lived ASCs and may not only impact improved cell therapies but also enhance strategies for vaccine development.

Stem cell-like T-bet+ IgM memory cells generate multi-lineage effector B cells

Abstract Our laboratory has been studying the differentiation of CD11c+ T-bet+ IgM memory B cells during secondary ehrlichial infection. These cells are closely related to B cells that have been described in a range of other contexts, including hepatitis, AIDs, malaria, SLE, and age-related autoimmunity. Following secondary infection, IgM memory cells, as a population, undergo self-renewal, and differentiate into effector cells, including splenic and bone marrow antibody secreting cells (ASC). Moreover, IgM memory cells enter germinal centers, where they undergo class-switch recombination and give rise to class-switched memory and effector cells. Although these data suggest that a single memory cell has multi-lineage potential, we sought to formally address this question by searching for shared clones among IgM memory cell-derived effector cells. Among the IgM memory cell-derived subsets, we identified several clones common to all effector cell populations. The number of common clones varied for each pairwise comparison of effector cells and suggested lineal relationships. IgM memory cells accumulated mutations following rechallenge; although all memory cell-derived subsets displayed similar numbers of V region mutations. Lineage analysis demonstrated that the effector cell subsets underwent varying degrees of clonal diversification, although this was clone-dependent. These studies reveal that a single IgM memory cell clone can give rise to different memory and effector cell subsets, that is, they exhibit stem cell properties. This property distinguishes these T-bet+ IgM memory cells as a unique memory cell subset.

Helper T cells are required for the development of IgM memory cells, but not IgM bone marrow plasmablasts

Abstract The processes and factors that regulate B cell fate decisions during IgM memory cell development and differentiation are unknown, and may differ from those required by canonical memory cells. In our experimental model of Ehrlichia muris infection, we have characterized two long-lived B cell populations: IgM memory cells, and IgM bone marrow (BM) antibody secreting cells (ASCs). The IgM+ memory B cells are required for recall IgG responses, while the BM ASCs produce antigen-specific IgM responsible for maintaining long-term immunity. Both populations are derived from an early AID-expressing CD4 T cell-independent splenic CD11c+ plasmablast population. Because abundant T follicular helper cells are generated in the spleen during early infection, we investigated whether T cell help regulates B cell fate. Infection of MHC class II-deficient mice revealed that the IgM+ memory B cells required CD4+ T cell help, while the IgM+ BM ASCs did not. Moreover, IgM memory cell transfer studies indicated that T cell help was required for the generation of IgM+ memory cells, but not for the generation of BM ASCs. On the basis of these observations, we propose that T cells drive B cell fate: developing spleen plasmablasts that receive T cell signals mature to become IgM memory cells, while cells that do not receive these signals follow a default pathway to become long-lived IgM BM ASCs.

CXCL13 promotes isotype-switched B cell accumulation to the central nervous system during viral encephalomyelitis

Elevated CXCL13 within the central nervous system (CNS) correlates with humoral responses in several neuroinflammatory diseases, yet its role is controversial. During coronavirus encephalomyelitis CXCL13 deficiency impaired CNS accumulation of memory B cells and antibody-secreting cells (ASC) but not naïve/early-activated B cells. However, despite diminished germinal center B cells and follicular helper T cells in draining lymph nodes, ASC in bone marrow and antiviral serum antibody were intact in the absence of CXCL13. The data demonstrate that CXCL13 is not essential in mounting effective peripheral humoral responses, but specifically promotes CNS accumulation of differentiated B cells.

Antibody isolation from immunized animals: comparison of phage display and antibody discovery via V gene repertoire mining

Phage display has enabled the rapid isolation of antigen-specific antibodies from combinatorial libraries of V(H) and V(L) genes obtained from lymphocytes of immunized animals. Recently, a different approach to antibody isolation that circumvents library screening and instead relies on the mining of the V(H) and V(L) gene repertoires obtained by high throughput sequencing of cDNAs from bone marrow antibody-secreting cells was reported. Here we compared the antibodies obtained via phage library screening or via repertoire mining of V gene cDNAs obtained from total splenocytes of mice immunized with the hapten trinitrophenyl (TNP) conjugated to carrier proteins. We show that, despite the large heterogeneity of B lymphocytes in the spleen, the most abundant V genes encoded antigen-specific antibodies, indicating that total splenocytes can be used in place of bone marrow plasma cells for antibody discovery at least in high titer animals. While both phage display and repertoire mining yielded antigen-specific antibodies showing comparable affinities by enzyme-linked immunosorbent assay analysis, clones obtained by the latter approach displayed higher selectivity towards TNP relative to control haptens. Interestingly, the antibody genes isolated by phage display were of low abundance or absent from the V gene repertoire obtained by 454 sequencing. Similarly, the highly abundant V genes identified by repertoire mining, that as soluble antibodies were antigen-specific, were found to be poorly displayed on phage and were not enriched by phage panning. Thus, our results reveal that phage display and repertoire mining of immune repertoires are complementary technologies that can yield different antigen-specific antibody clones.

Nasopharyngeal colonization by Streptococcus pneumoniae elicits long-lasting immune responses that confer protection from invasive lung infections (161.19)

Abstract Streptococcus pneumoniae can cause life-threatening pulmonary and systemic infection, but resides usually harmlessly in the nasopharynx of many people. Humoral immunity is thought to be the primary defense against serious pneumococcal infection, and we hypothesized that nasopharyngeal colonization of mice may result in the generation of an antibody response that provides long-term protection against lung infection. In fact, we found that intranasal colonization elicited pneumococcal-specific antibody responses and protected from a S. pneumoniae lung challenge that is lethal in naive mice. B cells were required for protection, and transfer of immune sera from colonized mice protected naive mice. CD93-/- mice, which are deficient in long-term antibody secreting cells (ASC), had fewer pneumococcal-specific bone marrow ASC after intranasal colonization and did not survive lung challenge. T cells were required to generate a fully protective response, but elimination of CD4+ T cells just prior to lung challenge did not compromise. These data are consistent with the hypothesis that CD4+ T cells promote the development of post-colonization immunity but are not needed to sustain the response that provides protection from lung challenge. These results stand in contrast to the T-cell independent antibody responses that are sufficient to protect mice from systemic infection, and have implications for development of effective vaccines.

Early appearance of germinal center–derived memory B cells and plasma cells in blood after primary immunization

Immunization with a T cell–dependent antigen elicits production of specific memory B cells and antibody-secreting cells (ASCs). The kinetic and developmental relationships between these populations and the phenotypic forms they and their precursors may take remain unclear. Therefore, we examined the early stages of a primary immune response, focusing on the appearance of antigen-specific B cells in blood. Within 1 wk, antigen-specific B cells appear in the blood with either a memory phenotype or as immunoglobulin (Ig)G1 ASCs expressing blimp-1. The memory cells have mutated VH genes; respond to the chemokine CXCL13 but not CXCL12, suggesting recirculation to secondary lymphoid organs; uniformly express B220; show limited differentiation potential unless stimulated by antigen; and develop independently of blimp-1 expression. The antigen-specific IgG1 ASCs in blood show affinity maturation paralleling that of bone marrow ASCs, raising the possibility that this compartment is established directly by blood-borne ASCs. We find no evidence for a blimp-1–expressing preplasma memory compartment, suggesting germinal center output is restricted to ASCs and B220+ memory B cells, and this is sufficient to account for the process of affinity maturation.

Long-term Persistence of Anti-factor VIII Antibody-secreting Cells in Hemophilic Mice after Treatment with Human Factor VIII

The analysis of anti-factor VIII (FVIII) antibody-secreting cells (ASC) at different anatomic sites provides valuable information about the nature of the anti-FVIII immune response in hemophilic mice after treatment with human FVIII. An Elispot system is described that is suitable for analyzing frequencies and IgG subclasses of anti-FVIII ASC at the single-cell level. Hemophilic mice were treated with four doses of FVIII. Anti-FVIII antibodies in blood as well as anti-FVIII ASC in spleen and bone marrow were analyzed after each dose of FVIII and subsequently up to 22 weeks after termination of the FVIII treatment. Anti-FVIII ASC first appeared in the spleen where they were detectable after two intravenous doses of FVIII. Their appearance correlated with that of anti-FVIII antibodies in blood plasma. Anti-FVIII ASC in bone marrow were detectable after three doses of FVIII and were probably cells that initially formed in the spleen and subsequently migrated to the bone marrow. Whereas the frequency of anti-FVIII ASC in the spleen increased up to the fourth dose of FVIII and declined thereafter, in the bone marrow it remained constant for up to at least 22 weeks after the termination of the FVIII treatment. Titers of anti-FVIII antibodies in blood plasma increased up to the fourth dose of FVIII, then remained high constantly for 14 weeks and decreased but the antibodies were still detectable for up to at least 22 weeks after the fourth dose of FVIII. The IgG-subclass distribution of anti-FVIII ASC was similar in spleen and bone marrow and matched the subclasses of anti-FVIII antibodies in blood plasma indicating that both organs contribute to circulating antibodies in the blood.

Delayed and deficient establishment of the long-term bone marrow plasma cell pool during early life.

Early life antibody responses are characterized by a rapid decline, such that antigen-specific IgG antibodies decline to baseline levels within months following infant immunization. This generic observation remains unexplained. Here, we have analyzed the induction and organ-localization of antigen-specific IgG antibody-secreting cells (ASC) following immunization of 1-week-old or adult BALB/c mice with tetanus toxoid (TT), a T-dependent antigen. Early life priming induced only slightly lower numbers of TT-specific IgG ASC in the spleen, and these reached adult levels following repeat immunization. In contrast, early life immunization generated much fewer bone marrow plasma cells than in adults, even after boosting. A similar limitation of the natural development of the bone marrow pool of ASC was observed. Transfer experiments with adult or early life spleen ASC indicated limited homing of TT-specific adult ASC to the bone marrow of 4-week-old mice as compared to adult recipients, whereas homing patterns were similar when early life or adult ASC were transferred into adult recipients. These observations suggest that a limited bone marrow B cell homing capacity and, as a result, relatively deficient bone marrow ASC responses, are critical factors which may explain the limited persistence of IgG antibodies to T-dependent antigens in early life.

Bone marrow is a major site of long-term antibody production after acute viral infection

Antiviral antibody production is often sustained for long periods after resolution of an acute viral infection. Despite extensive documentation of this phenomenon, the mechanisms involved in maintaining long-term antibody production remain poorly defined. As a first step towards understanding the nature of long-term humoral immunity, we examined the anatomical location of antibody-producing cells during acute viral infection. Using the lymphocytic choriomeningitis virus (LCMV) model, we found that after resolution of the acute infection, when antiviral plasma cells in the spleen decline, a population of virus-specific plasma cells appears in the bone marrow and constitutes the major source of long-term antibody production. Following infection of adult mice, LCMV-specific antibody-secreting cells (ASC) peaked in the spleen at 8 days postinfection but were undetectable in the bone marrow at that time. The infection was essentially cleared by 15 days, and the ASC numbers in the spleen rapidly declined while an increasing population of LCMV-specific ASC began to appear in the bone marrow. Compared with the peak response at 8 days postinfection, time points from 30 days to more than 1 year later demonstrated greater-than-10-fold reductions in splenic ASC. In contrast, LCMV-specific plasma cell numbers in the bone marrow remained high and correlated with the high levels of antiviral serum antibody. The presence of LCMV-specific plasma cells in the bone marrow was not due to persistent infection at this site, since the virus was cleared from both the spleen and bone marrow with similar kinetics as determined by infectivity and PCR assays. The immunoglobulin G subclass profile of antibody-secreting cells derived from bone marrow and the spleen correlated with the immunoglobulin G subclass distribution of LCMV-specific antibody in the serum. Upon rechallenge with LCMV, the spleen exhibited a substantial increase in virus-specific plasma cell numbers during the early phase of the secondary response, followed by an equally sharp decline. Bone marrow ASC populations and LCMV-specific antibody levels in the serum did not change during the early phase of the reinfection, but both increased about two-fold by 15 days postchallenge. After both primary and secondary viral infections, LCMV-specific plasma cells were maintained in the bone marrow, showing that the bone marrow is a major site of long-term antibody production after acute viral infection. These results documenting long-term persistence of plasma cells in the bone marrow suggest a reexamination of our current notions regarding the half-life of plasma cells.