Maintenance of serological memory by polyclonal activation of human memory B cells

Comparative immunogenicity and safety of human papillomavirus (HPV)-16/18 AS04-adjuvanted vaccine and 4vHPV vaccine administered according to two- or three-dose schedules in girls aged 9-14 years: Results to month 36 from a randomized trial

This observer-blind study (clinicaltrials.gov NCT01462357) compared the immunogenicity and safety of two doses (2D) of the HPV-16/18 AS04-adjuvanted vaccine (2D of AS04-HPV-16/18) vs. two or three doses of the 4vHPV vaccine [2D or 3D of 4vHPV] in 1075 healthy girls aged 9-14 years. Girls were randomized (1:1:1) to receive 2D of AS04-HPV-16/18 at months (M) 0, 6 (N = 359), 2D of 4vHPV at M0, 6 (N = 358) or 3D of 4vHPV at M0, 2, 6 (N = 358). 351, 339 and 346 girls, respectively, returned for the concluding visit at M36. Superiority was demonstrated at M7 and M12; comparison of the immune response to both vaccine antigens was made between 2D of AS04-HPV-16/18 and 2D or 3D of 4vHPV at subsequent time points in the according-to-protocol immunogenicity cohort (ATP-I; N = 958 at M36) and the total vaccinated cohort (TVC: N = 1036 at M36). HPV-16/18-specific T-cell- and B-cell-mediated immune responses and safety were also investigated. At M36, anti-HPV-16/18 ELISA responses in the 2D AS04-HPV-16/18 group remained superior to those of the 2D and 3D 4vHPV groups. In the M36 TVC, geometric mean titers were 2.78-fold (HPV-16) and 6.84-fold (HPV-18) higher for 2D of AS04-HPV-16/18 vs. 2D of 4vHPV and 2.3-fold (HPV-16) and 4.14-fold (HPV-18) higher vs. 3D of 4vHPV. Results were confirmed by vaccine pseudovirion-based neutralisation assay. Numbers of circulating CD4⁺ T cells and B cells appeared similar across groups. Safety was in line with the known safety profiles of both vaccines. In conclusion, superior HPV-16/18 antibody responses were elicited by 2D of the AS04-HPV-16/18 compared with 2D or 3D of the 4vHPV vaccine in girls aged 9-14 years.

CLINICAL TRIAL REGISTRATION

NCT0146235.

IL-15 enhances cross-reactive antibody recall responses to seasonal H3 influenza viruses in vitro

Background: Recently, several human monoclonal antibodies that target conserved epitopes on the stalk region of influenza hemagglutinin (HA) have shown broad reactivity to influenza A subtypes. Also, vaccination with recombinant chimeric HA or stem fragments from H3 influenza viruses induce broad immune protection in mice and humans. However, it is unclear whether stalk-binding antibodies can be induced in human memory B cells by seasonal H3N2 viruses.

Methods: In this study, we recruited 13 donors previously exposed to H3 viruses, the majority (12 of 13) of which had been immunized with seasonal influenza vaccines. We evaluated plasma baseline strain-specific and stalk-reactive anti-HA antibodies and B cell recall responses to inactivated H3N2 A/Victoria/361/2011 virus in vitro using a high throughput multiplex (mPlex-Flu) assay.

Results: Stalk-reactive IgG was detected in the plasma of 7 of the subjects. Inactivated H3 viral particles rapidly induced clade cross-reactive antibodies in B cell cultures derived from all 13 donors. In addition, H3 stalk-reactive antibodies were detected in culture supernatants from 7 of the 13 donors (53.8%).  H3 stalk-reactive antibodies were also induced by H1 and H7 subtypes. Interestingly, broadly cross-reactive antibody recall responses to H3 strains were also enhanced by stimulating B cells in vitro with CpG ₂₀₀₆ ODN in the presence of IL-15. H3 stalk-reactive antibodies were detected in  CpG ₂₀₀₆ ODN + IL-15 stimulated B cell cultures derived from 12 of the 13 donors (92.3%), with high levels detected in cultures from 7 of the 13 donors.

Conclusions: Our results demonstrate that stalk-reactive antibody recall responses induced by seasonal H3 viruses and CpG ₂₀₀₆ ODN can be enhanced by IL-15.

Evolving Approaches in the Identification of Allograft-Reactive T and B Cells in Mice and Humans

Whether a transplanted allograft is stably accepted, rejected, or achieves immunological tolerance is dependent on the frequency and function of alloreactive lymphocytes, making the identification and analysis of alloreactive T and B cells in transplant recipients critical for understanding mechanisms, and the prediction of allograft outcome. In animal models, tracking the fate of graft-reactive T and B cells allows investigators to uncover their biology and develop new therapeutic strategies to protect the graft. In the clinic, identification and quantification of graft-reactive T and B cells allows for the early diagnosis of immune reactivity and therapeutic intervention to prevent graft loss. In addition to rejection, probing of T and B cell fate in vivo provides insights into the underlying mechanisms of alloimmunity or tolerance that may lead to biomarkers predicting graft fate. In this review, we discuss existing and developing approaches to track and analyze alloreactive T and B cells in mice and humans and provide examples of discoveries made utilizing these techniques. These approaches include mixed lymphocyte reactions, trans-vivo delayed-type hypersensitivity, enzyme-linked immunospot assays, the use of antigen receptor transgenic lymphocytes, and utilization of peptide-major histocompatibility multimers, along with imaging techniques for static multiparameter analysis or dynamic in vivo tracking. Such approaches have already refined our understanding of the alloimmune response and are pointing to new ways to improve allograft outcomes in the clinic.

Optimisation of ex vivo memory B cell expansion/differentiation for interrogation of rare peripheral memory B cell subset responses

Background: Human memory B cells play a vital role in the long-term protection of the host from pathogenic re-challenge. In recent years the importance of a number of different memory B cell subsets that can be formed in response to vaccination or infection has started to become clear. To study memory B cell responses, cells can be cultured ex vivo, allowing for an increase in cell number and activation of these quiescent cells, providing sufficient quantities of each memory subset to enable full investigation of functionality. However, despite numerous papers being published demonstrating bulk memory B cell culture, we could find no literature on optimised conditions for the study of memory B cell subsets, such as IgM ⁺ memory B cells. Methods: Following a literature review, we carried out a large screen of memory B cell expansion conditions to identify the combination that induced the highest levels of memory B cell expansion. We subsequently used a novel Design of Experiments approach to finely tune the optimal memory B cell expansion and differentiation conditions for human memory B cell subsets. Finally, we characterised the resultant memory B cell subpopulations by IgH sequencing and flow cytometry. Results: The application of specific optimised conditions induce multiple rounds of memory B cell proliferation equally across Ig isotypes, differentiation of memory B cells to antibody secreting cells, and importantly do not alter the Ig genotype of the stimulated cells.  Conclusions: Overall, our data identify a memory B cell culture system that offers a robust platform for investigating the functionality of rare memory B cell subsets to infection and/or vaccination.

Optimisation of ex vivo memory B cell expansion/differentiation for interrogation of rare peripheral memory B cell subset responses

Background:Human memory B cells play a vital role in the long-term protection of the host from pathogenic re-challenge. In recent years the importance of a number of different memory B cell subsets that can be formed in response to vaccination or infection has started to become clear. To study memory B cell responses, cells can be culturedex vivo,allowing for an increase in cell number and activation of these quiescent cells, providing sufficient quantities of each memory subset to enable full investigation of functionality. However, despite numerous papers being published demonstrating bulk memory B cell culture, we could find no literature on optimised conditions for the study of memory B cell subsets, such as IgM+memory B cells.Methods:Following a literature review, we carried out a large screen of memory B cell expansion conditions to identify the combination that induced the highest levels of memory B cell expansion. We subsequently used a novel Design of Experiments approach to finely tune the optimal memory B cell expansion and differentiation conditions for human memory B cell subsets. Finally, we characterised the resultant memory B cell subpopulations by IgH sequencing and flow cytometry.Results:The application of specific optimised conditions induce multiple rounds of memory B cell proliferation equally across Ig isotypes, differentiation of memory B cells to antibody secreting cells, and importantly do not alter the Ig genotype of the stimulated cells. Conclusions:Overall, our data identify a memory B cell culture system that offers a robust platform for investigating the functionality of rare memory B cell subsets to infection and/or vaccination.

Epitope-associated and specificity-focused features of EV71-neutralizing antibody repertoires from plasmablasts of infected children

Protective antibody levels are critical for protection from severe enterovirus 71 infection. However, little is known about the specificities and functional properties of the enterovirus 71-specific antibodies induced by natural infection in humans. Here we characterize 191 plasmablast-derived monoclonal antibodies from three enterovirus 71-infected children, each of whom shows a distinct serological response. Of the 84 enterovirus 71-specific antibodies, neutralizing antibodies that target the rims and floor of the capsid canyon exhibit broad and potent activities at the nanogram level against viruses isolated in 1998–2016. We also find a subset of infected children whose enterovirus 71-specific antibodies are focused on the 3- and 2-fold plateau epitopes localized at the margin of pentamers, and this type of antibody response is associated with lower serum titers against recently circulating strains. Our data provide new insights into the enterovirus 71-specific antibodies induced by natural infection at the serological and clonal levels.

Enterovirus 71 is a leading cause of hand-foot-and-mouth disease and herpangina. Here, the authors characterize a large panel of plasmablast-derived IgG mAbs that target the capsid of EV71 to identify neutralizing antibodies induced by natural infection.

A Memory B Cell Crossmatch Assay for Quantification of Donor-Specific Memory B Cells in the Peripheral Blood of HLA-Immunized Individuals

Humoral responses against mismatched donor HLA are routinely measured as serum HLA antibodies, which are mainly produced by bone marrow-residing plasma cells. Individuals with a history of alloimmunization but lacking serum antibodies may harbor circulating dormant memory B cells, which may rapidly become plasma cells on antigen reencounter. Currently available methods to detect HLA-specific memory B cells are scarce and insufficient in quantifying the complete donor-specific memory B cell response due to their dependence on synthetic HLA molecules. We present a highly sensitive and specific tool for quantifying donor-specific memory B cells in peripheral blood of individuals using cell lysates covering the complete HLA class I and class II repertoire of an individual. Using this enzyme-linked immunospot (ELISpot) assay, we found a median frequency of 31 HLA class I and 89 HLA class II-specific memory B cells per million IgG-producing cells directed at paternal HLA in peripheral blood samples from women (n = 22) with a history of pregnancy, using cell lysates from spouses. The donor-specific memory B cell ELISpot can be used in HLA diagnostic laboratories as a cross-match assay to quantify donor-specific memory B cells in patients with a history of sensitizing events.

Verification of post-chemotherapeutic clearance of Theileria equi through concordance of nested PCR and immunoblot

Certain countries including the United States remain non-endemic for particular infectious diseases such as equine piroplasmosis through import restrictions and surveillance. Endemic regions often employ premunition as the primary method to control disease, however in non-endemic countries, chemosterilization combined with methods to confirm parasite elimination are required to maintain disease-free status. The ability of imidocarb diproprionate (ID) to clear persistent Theileria equi infection from infected horses has been shown through the inability of treated horses to transmit via blood transfer. However, the common lengthy persistence of anti-T. equi antibody causes regulatory tests such as cELISA or IFA to remain positive for extended periods. Persistence of positive testing creates challenges for regulatory veterinary medicine and international trade. Concordance between nested polymerase chain reaction (nPCR) targeting the ema1 gene and immunoblotting (IB) measuring declination in anti-EMA1 and anti-EMA2 antibody were used to verify clearance of T. equi from 179 ID-treated horses. These data support the use of IB to demonstrate declining anti-EMA1 and EMA2 titers in T. equi-infected horses subsequent to successful ID treatment. Such data provide concordant support to a negative nPCR and allow for a more timely determination of effective ID clearance of T. equi. The post ID treatment results indicate that while nPCR was consistently negative by 14 days and cELISA generally remained positive after 1 year, immunoblot was on average negative after 4 months and 100% in agreement with nPCR.

Longevity of protective immune responses induced by a split influenza A (H7N9) vaccine mixed with MF59 adjuvant in BALB/c mice

The influenza virus is a serious threat to public health worldwide. A novel avian influenza A (H7N9) virus with a mortality rate of approximately 30% has been identified as an unusually dangerous virus for humans by the World Health Organization. Pathogenic H7N9 continue to represent a public health concern, and several candidate vaccines are currently in development. We generated candidate H7N9 vaccine strains using reverse genetics, consisting of hemagglutinin and neuraminidase genes derived from a human H7N9 virus and the remaining genes from the PR8 (A/PuertoRico/8/34 (H1N1)) virus. This H7N9 vaccine exhibited superior efficacy when combined with MF59 compared to other adjuvants. Immunized BALB/c mice were followed to determine the duration of the protective immune response. Antibody levels decreased to between one-half and one-eighth of the peak values four months after the final dose of the vaccine. Previously vaccinated mice received an A/Zhejiang/DTID-ZJU01/2013 H7N9 challenge six months post-vaccination, and all remained protected. We also verified that MF59 enhanced the HI, MN, and IgG antibody titers to influenza antigens. The humoral immune response and Th2 cytokine production following influenza challenge was potently induced in the animals that received the split vaccine. Therefore, the split H7N9 influenza vaccine with the MF59 adjuvant could effectively induce antibody production and protect mice from H7N9 virus challenge even after six months.

A recombinant protein of Salmonella Typhi induces humoral and cell-mediated immune responses including memory responses

Gram negative enteric bacteria, Salmonella enterica serovar Typhi (S. Typhi), the etiological agent of typhoid fever is a major public health problem in developing countries. While a permanent solution to the problem would require improved sanitation, food and water hygiene, controlling the infection by vaccination is urgently required due to the emergence of multidrug resistant strains in multiple countries. The currently licensed vaccines are moderately efficacious with limited applicability, and no recommended vaccines exist for younger children. We had previously reported that a candidate vaccine based on recombinant outer membrane protein (rT2544) of S. Typhi is highly immunogenic and protective in mice. Here we show that rT2544-specific antiserum is capable of mediating bacterial lysis by the splenocytes through Antibody-Dependent Cellular Cytotoxicity (ADCC). Increased populations of rT2544-specific IgA and IgG secreting plasma cells are found in the spleen, mesenteric lymph nodes and peyer's patches. Cell-Mediated Immune Responses (CMIR) induced by rT2544 consist of Th1 cell differentiation and generation of cytotoxic T lymphocytes (CTL), which produce IFN-γ and are capable of destroying cells displaying T2544-derived antigens. rT2544 elicits pro-inflammatory cytokines (TNF-α, IL-6) from Bone Marrow-Derived Dendritic cells (BMDCs), while in vitro re-stimulation of rT2544-primed CD4+ T cells induces cell proliferation and generates higher amounts of Th1 cytokines, such as IFN-gamma, TNF-α and IL-2. Finally, the candidate vaccine induces immunological memory in the form of memory B and T lymphocytes. Taken together, the study further supports the potential of rT2544 as a novel and improved vaccine candidate against S. Typhi.

Application of Epstein-Barr Virus for Optimization of Immortalized B-lymphocyte Production as a Positive Control in Genetic Studies

BACKGROUND

Infection of B-cells with Epstein-Barr virus (EBV) leads to more and subsequent immortalization. This is considered as the method of choice for generating lymphoblastoid cell lines (LCLs). Producing LCLs, although very useful but is very time consuming and troublesome, drives the requirement for quicker and more reliable methods for EBV-driven B-cell transformation.

MATERIALS AND METHODS

After successfully production of LCLs, different parameters including temperature, serum concentration, type of culture medium, and CO₂ concentration were evaluated on EBV-transformed B-cells. In this study, we were able to produce LCLs and optimize condition.

RESULTS

The best condition for generating LCLs was 37°C, 5% CO₂, 20% fasting blood sugar, and RPMI 1640. The study results were to establish a reliable method for producing LCLs that can be used to produce immortalized B-cells from almost any sources.

CONCLUSION

This can help with tumorgenecity studies, as well as producing control material for rare genetic disorders and so on. The aim of this study was to determine optimized condition for reliable and reproducible LCLs from different sources.

Antibody therapies for the prevention and treatment of viral infections

Antibodies are an important component in host immune responses to viral pathogens. Because of their unique maturation process, antibodies can evolve to be highly specific to viral antigens. Physicians and researchers have been relying on such high specificity in their quest to understand host–viral interaction and viral pathogenesis mechanisms and to find potential cures for viral infection and disease. With more than 60 recombinant monoclonal antibodies developed for human use in the last 20 years, monoclonal antibodies are now considered a viable therapeutic modality for infectious disease targets, including newly emerging viral pathogens such as Ebola representing heightened public health concerns, as well as pathogens that have long been known, such as human cytomegalovirus. Here, we summarize some recent advances in identification and characterization of monoclonal antibodies suitable as drug candidates for clinical evaluation, and review some promising candidates in the development pipeline.

From lymphopoiesis to plasma cells differentiation, the age-related modifications of B cell compartment are influenced by "inflamm-ageing"

Ageing is a complex process characterized by a general decline in physiological functions with increasing morbidity and mortality. The most important aspect of ageing is the chronic inflammatory status, named "inflamm-ageing", strictly associated with the deterioration of the immune function, termed "immunosenescence". Both are causes of increased susceptibility of elderly to infectious diseases, cancer, dementia, cardiovascular diseases and autoimmunity, and of a decreased response to vaccination. It has been widely demonstrated that ageing has a strong impact on the remodelling of the B cell branch of immune system. The first evident effect is the significant decrease in circulating B cells, primarily due to the reduction of new B cell coming from bone marrow (BM) progenitors, as inflammation directly impacts on B lymphopoiesis. Besides, in aged individuals, there is a shift from naïve to memory immunoglobulins production, accompanied by the impaired ability to produce high affinity protective antibodies against newly encountered antigens. This is accompanied by the increase of expanded clones of B cells, which correlates with poor health status. Age-related modifications also occur in naïve/memory B cells subsets. Indeed, in the elderly, there is a reduction of naïve B cells, accompanied by the expansion of memory B cells that show a senescence-associated phenotype. Finally, elderly show the impaired ability of memory B cells to differentiate into plasma cells. It can be concluded that inflammation is the leading cause of the age-related impairment of B cell compartment, which play certainly a key role in the development of age-related diseases. This makes study of B cells in the aged an important tool for monitoring immunosenescence, chronic inflammatory disorders and the effectiveness of vaccines or pharmacological therapies.

A label-free immunoassay for Flavivirus detection by the Reflective Phantom Interface technology

Flaviviruses are widespread and cause clinically relevant arboviral diseases that impact locally and as imported travel-related infections. Direct detection of viraemia is limited, being typically undetectable at onset of symptoms. Therefore, diagnosis is primarily based on serology, which is complicated by high cross-reactivity across different species. The overlapping geographical distribution of the vectors in areas with a weak healthcare system, the increase of international travel and the similarity of symptoms highlight the need for rapid and reliable multi-parametric diagnostic tests in point-of-care formats. To this end we developed a bi-parametric serological microarray using recombinant NS1 proteins from Tick-borne encephalitis virus and West Nile virus coupled to a low-cost, label-free detection device based on the Reflective Phantom Interface (RPI) principle. Specific sequential detection of antibodies in solution demonstrates the feasibility of the approach for the surveillance and diagnosis of Flaviviruses.

CNS Aquaporin-4-specific B cells connect with multiple B-cell compartments in neuromyelitis optica spectrum disorder

Objectives

Neuromyelitis optica spectrum disorder (NMOSD) is a severe inflammatory disorder of the central nervous system (CNS) targeted against aquaporin‐4 (AQP4). The origin and trafficking of AQP4‐specific B cells in NMOSD remains unknown.

Methods

Peripheral (n = 7) and splenic B cells (n = 1) recovered from seven NMOSD patients were sorted into plasmablasts, naïve, memory, and CD27‐IgD‐ double negative (DN) B cells, and variable heavy chain (VH) transcriptome sequences were generated by deep sequencing. Peripheral blood (PB) VH repertoires were compared to the same patient's single‐cell cerebrospinal fluid (CSF) plasmablast (PB) VH transcriptome, CSF immunoglobulin (Ig) proteome, and serum Ig proteome. Recombinant antibodies were generated from paired CSF heavy‐ and light chains and tested for AQP4 reactivity.

Results

Approximately 9% of the CSF VH sequences aligned with PB memory B cells, DN B cells, and plasmablast VH sequences. AQP4‐specific VH sequences were observed in each peripheral B‐cell compartment. Lineage analysis of clonally related VH sequences indicates that CSF AQP4‐specific B cells are closely related to an expanded population of DN B cells that may undergo antigen‐specific B‐cell maturation within the CNS. CSF and serum Ig proteomes overlapped with the VH sequences from each B‐cell compartment; the majority of matches occurring between the PB VH sequences and serum Ig proteome.

Interpretation

During an acute NMOSD relapse, a dynamic exchange of B cells occurs between the periphery and CNS with AQP4‐specific CSF B cells emerging from postgerminal center memory B cells and plasmablasts. Expansion of the PB DN B‐cell compartment may be a potential biomarker of NMOSD activity.

An optimized method for enumerating CNS derived memory B cells during viral-induced inflammation

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Memory B cell markers characterizing peripheral B cell phenotypes show more diverse expression patterns in the infected central nervous system (CNS).

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TLR7/8 stimulation for 2 days prior to ELISPOT analysis achieves optimal conversion of CNS-derived memory B cells to ASC while minimizing cell loss.

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In vitro stimulation allows simultaneous assessment of antibody secreting cell and memory B cell isotype, antigen specificity, and temporal alterations during CNS inflammation.

Background

CNS inflammation resulting from infection, injury, or neurodegeneration leads to accumulation of diverse B cell subsets. Although antibody secreting cells (ASC) within the inflamed CNS have been extensively examined, memory B cell (Bmem) characterization has been limited as they do not secrete antibody without stimulation. Moreover, unlike human Bmem, reliable surface markers for murine Bmem remain elusive.

New method

Using a viral encephalomyelitis model we developed a modified limiting dilution in vitro stimulation assay to convert CNS-derived virus specific Bmem into ASC.

Comparison with existing methods

Stimulation methods established for lymphoid tissue cells using prolonged stimulation with viral lysate resulted in substantial ASC loss and minimal Bmem to ASC conversion of CNS-derived cells. By varying stimulation duration, TLR activators, and culture supplements, we achieved optimal conversion by culturing cells with TLR7/8 agonist R848 in the presence of feeder cells for 2 days.

Results

Flow cytometry markers CD38 and CD73 characterizing murine Bmem from lymphoid tissue showed more diverse expression patterns on corresponding CNS-derived B cell subsets. Using the optimized TLR7/8 stimulation protocol, we compared virus-specific IgG Bmem versus pre-existing ASC within the brain and spinal cord. Increasing Bmem frequencies during chronic infection mirrored kinetics of ASC. However, despite initially similar Bmem and ASC accumulation, Bmem prevailed in the brain, but were lower than ASC in the spinal cord during persistence.

Conclusion

Simultaneous enumeration of antigen-specific Bmem and ASC using the Bmem assay optimized for CNS-derived cells enables characterization of temporal changes during microbial or auto-antigen induced neuroinflammation.

Memory B Cells of Mice and Humans

We comprehensively review memory B cells (MBCs), covering the definition of MBCs and their identities and subsets, how MBCs are generated, where they are localized, how they are maintained, and how they are reactivated. Whereas naive B cells adopt multiple fates upon stimulation, MBCs are more restricted in their responses. Evolving work reveals that the MBC compartment in mice and humans consists of distinct subpopulations with differing effector functions. We discuss the various approaches to define subsets and subset-specific roles. A major theme is the need to both deliver faster effector function upon reexposure and readapt to antigenically variant pathogens while avoiding burnout, which would be the result if all MBCs generated only terminal effector function. We discuss cell-intrinsic differences in gene expression and signaling that underlie differences in function between MBCs and naive B cells and among MBC subsets and how this leads to memory responses.

TSLP-activated dendritic cells induce human T follicular helper cell differentiation through OX40-ligand

T follicular helper cells (Tfh) are implicated in various pathological conditions, but how they differentiate in Th2-skewed environments is unknown. Pattarini et al. delineate a pathway for human Tfh differentiation induced by TSLP through OX40L, relevant to atopic dermatitis.

T follicular helper cells (Tfh) are important regulators of humoral responses. Human Tfh polarization pathways have been thus far associated with Th1 and Th17 polarization pathways. How human Tfh cells differentiate in Th2-skewed environments is unknown. We show that thymic stromal lymphopoietin (TSLP)–activated dendritic cells (DCs) promote human Tfh differentiation from naive CD4 T cells. We identified a novel population, distinct from Th2 cells, expressing IL-21 and TNF, suggestive of inflammatory cells. TSLP-induced T cells expressed CXCR5, CXCL13, ICOS, PD1, BCL6, BTLA, and SAP, among other Tfh markers. Functionally, TSLP-DC–polarized T cells induced IgE secretion by memory B cells, and this depended on IL-4Rα. TSLP-activated DCs stimulated circulating memory Tfh cells to produce IL-21 and CXCL13. Mechanistically, TSLP-induced Tfh differentiation depended on OX40-ligand, but not on ICOS-ligand. Our results delineate a pathway of human Tfh differentiation in Th2 environments.

The B Cell Response to Foot-and-Mouth Disease Virus in Cattle following Sequential Vaccination with Multiple Serotypes

Foot-and-mouth disease virus (FMDV) is a highly contagious viral disease. Antibodies are pivotal in providing protection against FMDV infection. Serological protection against one FMDV serotype does not confer interserotype protection. However, some historical data have shown that interserotype protection can be induced following sequential FMDV challenge with multiple FMDV serotypes. In this study, we have investigated the kinetics of the FMDV-specific antibody-secreting cell (ASC) response following homologous and heterologous inactivated FMDV vaccination regimes. We have demonstrated that the kinetics of the B cell response are similar for all four FMDV serotypes tested following a homologous FMDV vaccination regime. When a heterologous vaccination regime was used with the sequential inoculation of three different inactivated FMDV serotypes (O, A, and Asia1 serotypes) a B cell response to FMDV SAT1 and serotype C was induced. The studies also revealed that the local lymphoid tissue had detectable FMDV-specific ASCs in the absence of circulating FMDV-specific ASCs, indicating the presence of short-lived ASCs, a hallmark of a T-independent 2 (TI-2) antigenic response to inactivated FMDV capsid.IMPORTANCE We have demonstrated the development of intraserotype response following a sequential vaccination regime of four different FMDV serotypes. We have found indication of short-lived ASCs in the local lymphoid tissue, further evidence of a TI-2 response to FMDV.

Memory B cell response to a PCV-13 booster in 3.5year old children primed with either PCV-7 or PCV-13

Pneumococcal protein-polysaccharide conjugate vaccines provide direct protection against Streptococcus pneumoniae through the induction of persistent anti-polysaccharide antibodies, and by priming for a rapid secondary antibody response. Memory B cells (B_MEM) generated during an initial immune response are responsible for both the more rapid and quantitatively greater secondary antibody response and are also thought to contribute to the ongoing production of plasma cells providing long-term antibody persistence. We recruited 3.5-year-old children who had participated in a previous clinical trial comparing infant immunization with either a 7-valent (PCV-7) or a 13-valent pneumococcal conjugate vaccine (PCV-13) to investigate whether prior priming with pneumococcal antigens influences B_MEM responses. Blood was taken before and 1month after a PCV-13 booster. B_MEM were quantified using a cultured ELISpot assay for pneumococcal serotypes 1, 3, 4, 14, 19A, 23F, and with diphtheria and tetanus toxoid as controls, and then correlated with serotype-specific IgG concentrations and opsonophagocytic activity (OPA) titers. In total, blood samples from 62 participants were available for analysis. Serotype-specific B_MEM frequencies were generally low at baseline (before boost) although for serotypes 14 and 3, they were significantly higher in children primed with PCV-13 than PCV-7 primed children. Following the PCV-13 booster, B_MEM frequencies increased and were not different between the groups for all serotypes. A strong inverse correlation was found between antibody concentrations and OPA titers at baseline and B_MEM following booster vaccination for serotype 3 but not for other serotypes suggesting that, for this serotype, pre-existing serotype-specific antibodies may inhibit B_MEM formation in response to vaccination. Clinicaltrials.gov registration number: NCT01095471.

Comment on "Diversification of the antigen-specific T cell receptor repertoire after varicella zoster vaccination"

Analysis of antigen-specific T cells can be confounded by T cell activation in vitro.

T Regulatory Cells Support Plasma Cell Populations in the Bone Marrow

Long-lived plasma cells (PCs) in the bone marrow (BM) are a critical source of antibodies after infection or vaccination, but questions remain about the factors that control PCs. We found that systemic infection alters the BM, greatly reducing PCs and regulatory T (Treg) cells, a population that contributes to immune privilege in the BM. The use of intravital imaging revealed that BM Treg cells display a distinct behavior characterized by sustained co-localization with PCs and CD11c-YFP+ cells. Gene expression profiling indicated that BM Treg cells express high levels of Treg effector molecules, and CTLA-4 deletion in these cells resulted in elevated PCs. Furthermore, preservation of Treg cells during systemic infection prevents PC loss, while Treg cell depletion in uninfected mice reduced PC populations. These studies suggest a role for Treg cells in PC biology and provide a potential target for the modulation of PCs during vaccine-induced humoral responses or autoimmunity.

Lifelong memory responses perpetuate humoral TH2 immunity and anaphylaxis in food allergy

BACKGROUND

A number of food allergies (eg, fish, shellfish, and nuts) are lifelong, without any disease-transforming therapies, and unclear in their underlying immunology. Clinical manifestations of food allergy are largely mediated by IgE. Although persistent IgE titers have been attributed conventionally to long-lived IgE⁺ plasma cells (PCs), this has not been directly and comprehensively tested.

OBJECTIVE

We sought to evaluate mechanisms underlying persistent IgE and allergic responses to food allergens.

METHODS

We used a model of peanut allergy and anaphylaxis, various knockout mice, adoptive transfer experiments, and in vitro assays to identify mechanisms underlying persistent IgE humoral immunity over almost the entire lifespan of the mouse (18-20 months).

RESULTS

Contrary to conventional paradigms, our data show that clinically relevant lifelong IgE titers are not sustained by long-lived IgE⁺ PCs. Instead, lifelong reactivity is conferred by allergen-specific long-lived memory B cells that replenish the IgE⁺ PC compartment. B-cell reactivation requires allergen re-exposure and IL-4 production by CD4 T cells. We define the half-lives of antigen-specific germinal centers (23.3 days), IgE⁺ and IgG₁⁺ PCs (60 and 234.4 days, respectively), and clinically relevant cell-bound IgE (67.3 days).

CONCLUSIONS

These findings can explain lifelong food allergies observed in human subjects as the consequence of allergen exposures that recurrently activate memory B cells and identify these as a therapeutic target with disease-transforming potential.

Massive plasmablast response elicited in the acute phase of hantavirus pulmonary syndrome

Beside its key diagnostic value, the humoral immune response is thought to play a protective role in hantavirus pulmonary syndrome. However, little is known about the cell source of these antibodies during ongoing human infection. Herein we characterized B-cell subsets circulating in Andes-virus-infected patients. A notable potent plasmablast (PB) response that increased 100-fold over the baseline levels was observed around 1 week after the onset of symptoms. These PB present a CD3^neg CD19^low CD20^neg CD38^hi CD27^hi CD138^+/- IgA^+/- surface phenotype together with the presence of cytoplasmic functional immunoglobulins. They are large lymphocytes (lymphoblasts) morphologically coincident with the 'immunoblast-like' cells that have been previously described during blood cytology examinations of hantavirus-infected patients. Immunoreactivity analysis of white blood cell lysates suggests that some circulating PB are virus-specific but we also observed a significant increase of reactivity against virus-unrelated antigens, which suggests a possible bystander effect by polyclonal B-cell activation. The presence of this large and transient PB response raises the question as to whether these cells might have a protective or pathological role during the ongoing hantavirus pulmonary syndrome and suggest their practical application as a diagnostic/prognostic biomarker.

Dengue: knowledge gaps, unmet needs, and research priorities

Dengue virus is a mosquito-borne pathogen that causes up to about 100 million cases of disease each year, placing a major public health, social, and economic burden on numerous low-income and middle-income countries. Major advances by investigators, vaccine developers, and affected communities are revealing new insights and enabling novel interventions and approaches to dengue prevention and control. Such research has highlighted further questions about both the basic understanding of dengue and efforts to develop new tools. In this report, the third in a Series on dengue, we discuss existing approaches to dengue diagnostics, disease prognosis, surveillance, and vector control in low-income and middle-income countries, as well as potential consequences of vaccine introduction. We also summarise current knowledge and recent insights into dengue epidemiology, immunology, and pathogenesis, and their implications for understanding natural infection and current and future vaccines.

Altered B cell homeostasis and Toll-like receptor 9-driven response in patients affected by autoimmune polyglandular syndrome Type 1: Altered B cell phenotype and dysregulation of the B cell function in APECED patients

APECED is a T-cell mediated disease with increased frequencies of CD8+ effector and reduction of FoxP3+ T regulatory cells. Antibodies against affected organs and neutralizing to cytokines are found in the peripheral blood. The contribution of B cells to multiorgan autoimmunity in Aire-/- mice was reported opening perspectives on the utility of anti-B cell therapy. We aimed to analyse the B cell phenotype of APECED patients compared to age-matched controls. FACS analysis was conducted on PBMC in basal conditions and following CpG stimulation. Total B and switched memory (SM) B cells were reduced while IgM memory were increased in patients. In those having more than 15 years from the first clinical manifestation the defect included also mature and transitional B cells; total memory B cells were increased, while SM were unaffected. In patients with shorter disease duration, total B cells were unaltered while SM and IgM memory behaved as in the total group. A defective B cell proliferation was detected after 4day-stimulation. In conclusion APECED patients show, in addition to a significant alteration of the B cell phenotype, a dysregulation of the B cell function involving peripheral innate immune mechanisms particularly those with longer disease duration.

Interleukin-21 Drives Proliferation and Differentiation of Porcine Memory B Cells into Antibody Secreting Cells

Immunological prevention of infectious disease, especially viral, is based on antigen-specific long-lived memory B cells. To test for cellular proliferation and differentiation factors in swine, an outbred model for humans, CD21+ B cells were activated in vitro with CD40L and stimulated with purported stimulatory cytokines to characterize functional responses. IL-21 induced a 3-fold expansion in total cell numbers with roughly 15% of all B cells differentiating to IgM or IgG antibody secreting cells (ASCs.) However, even with robust proliferation, cellular viability rapidly deteriorated. Therefore, a proliferation inducing ligand (APRIL) and B cell activating factor (BAFF) were evaluated as survival and maintenance factors. BAFF was effective at enhancing the viability of mature B cells as well as ASCs, while APRIL was only effective for ASCs. Both cytokines increased approximately two-fold the amount of IgM and IgG which was secreted by IL-21 differentiated ASCs. Mature B cells from porcine reproductive and respiratory virus (PRRSV) immune and naïve age-matched pigs were activated and treated with IL-21 and then tested for memory cell differentiation using a PRRSV non-structural protein 7 ELISPOT and ELISA. PRRSV immune pigs were positive on both ELISPOT and ELISA while naïve animals were negative on both assays. These results highlight the IL-21-driven expansion and differentiation of memory B cells in vitro without stimulation of the surface immunoglobulin receptor complex, as well as the establishment of a defined memory B cell culture system for characterization of vaccine responses in outbred animals.

CpG oligodeoxynucleotide nanomedicines for the prophylaxis or treatment of cancers, infectious diseases, and allergies

Unmethylated cytosine-guanine dinucleotide-containing oligodeoxynucleotides (CpG ODNs), which are synthetic agonists of Toll-like receptor 9 (TLR9), activate humoral and cellular immunity and are being developed as vaccine adjuvants to prevent or treat cancers, infectious diseases, and allergies. Free CpG ODNs have been used in many clinical trials implemented to verify their effects. However, recent research has reported that self-assembled CpG ODNs, protein/peptide–CpG ODN conjugates, and nanomaterial–CpG ODN complexes demonstrate higher adjuvant effects than free CpG ODNs, owing to their improved uptake efficiency into cells expressing TLR9. Moreover, protein/peptide–CpG ODN conjugates and nanomaterial–CpG ODN complexes are able to deliver CpG ODNs and antigens (or allergens) to the same types of cells, which enables a higher degree of prophylaxis or therapeutic effect. In this review, the author describes recent trends in the research and development of CpG ODN nanomedicines containing self-assembled CpG ODNs, protein/peptide–CpG ODN conjugates, and nanomaterial–CpG ODN complexes, focusing mainly on the results of preclinical and clinical studies.

Moving Biomarkers toward Clinical Implementation in Kidney Transplantation

Long-term kidney transplant outcomes remain suboptimal, delineating an unmet medical need. Although current immunosuppressive therapy in kidney transplant recipients is effective, dosing is conventionally adjusted empirically on the basis of time after transplant or altered in response to detection of kidney dysfunction, histologic evidence of allograft damage, or infection. Such strategies tend to detect allograft rejection after significant injury has already occurred, fail to detect chronic subclinical inflammation that can negatively affect graft survival, and ignore specific risks and immune mechanisms that differentially contribute to allograft damage among transplant recipients. Assays and biomarkers that reliably quantify and/or predict the risk of allograft injury have the potential to overcome these deficits and thereby, aid clinicians in optimizing immunosuppressive regimens. Herein, we review the data on candidate biomarkers that we contend have the highest potential to become clinically useful surrogates in kidney transplant recipients, including functional T cell assays, urinary gene and protein assays, peripheral blood cell gene expression profiles, and allograft gene expression profiles. We identify barriers to clinical biomarker adoption in the transplant field and suggest strategies for moving biomarker-based individualization of transplant care from a research hypothesis to clinical implementation.

Temporal stability and molecular persistence of the bone marrow plasma cell antibody repertoire

Plasma cells in human bone marrow (BM) are thought to be responsible for sustaining lifelong immunity, but its underlying basis is controversial. Here we use high-throughput sequence analysis of the same individual across 6.5 years to show that the BM plasma cell immunoglobulin heavy chain repertoire is remarkably stable over time. We find a nearly static bias in individual and combinatorial gene usage across time. Analysis of a second donor corroborates these observations. We also report the persistence of numerous BM plasma cell clonotypes (∼2%) identifiable at all points assayed across 6.5 years, supporting a model of serological memory based upon intrinsic longevity of human plasma cells. Donors were adolescents who completely recovered from neuroblastoma prior to the start of this study. Our work will facilitate differentiation between healthy and diseased antibody repertoires, by serving as a point of comparison with future deep-sequencing studies involving immune intervention.

Longevity of antibody responses has been attributed to persistence of plasma cells in mice. Here the authors provide human data in support of this model by immunoglobulin sequencing bone marrow sections from two human donors over 6.5 years to show temporal stability of plasma cell clonotypes, but not other B cells.

B cells establish, but do not maintain, long-lived murine anti-peanut IgE(a)

BACKGROUND

Peanut allergy (PNA) has been reported to be transferred to tolerant recipients through organ and bone marrow (BM) transplantation. The roles T and B cells play in establishing, and the roles B cell subsets play in maintaining lifelong anti-peanut IgE levels are unknown.

OBJECTIVES

To determine the cellular requirements for the transfer of murine PNA and to determine the role CD20(+) cells play in maintaining long-lived anti-peanut IgE levels.

METHODS

We developed a novel adoptive transfer model to investigate the cellular requirements for transferring murine PNA. We also treated peanut-allergic (PA) mice with anti-CD20 antibody and measured IgE levels throughout treatment.

RESULTS

Purified B220(+) cells from PA splenocytes and purified CD4(+) cells from naïve (NA) splenocytes are the minimal requirements for the adoptive transfer of PNA. Prolonged treatment of allergic mice with anti-CD20 antibody results in significant depletion of B cell subsets but does not affect anti-peanut IgE levels, symptoms, or numbers of IgE antibody secreting cells (ASCs) in the BM. Adoptive transfer of BM and spleen cells from allergic donors treated with anti-CD20 antibody does not result in the transfer of PNA in NA recipients, demonstrating that anti-CD20 antibody treatment depletes B cells capable of differentiating into peanut-specific IgE ASCs.

CONCLUSIONS AND CLINICAL RELEVANCE

Peanut allergy can be established in a NA hosts with B220(+) cells from PA donors and CD4(+) cells from peanut-NA donors. However, long-term depletion of B220(+) cells with anti-CD20 antibody does not affect anti-peanut IgE levels. These results highlight a novel role for B cells in the development of PNA and provide evidence that long-lived anti-peanut IgE levels may be maintained by long-lived ASCs.

Rapid and strong de novo donor-specific antibody development in a lung transplant recipient: Short communication/case report

A 66-yo female patient (typed B*39:01, 44:02) underwent first left single lung transplant (typed B*81:01, 15:17) on 02/07/2016 with negative for DSA in current and historical samples. On 02/17/2016 strong de novo DSA (MFI=15,200, C1q+) to B81 were detected. The recipient has two children typed B*07:02, 44:02 B*27:03, 39:01, and had received multiple vaccinations. Twinrix, Zostavax and MMR vaccines contain viruses grown on live human lung fibroblasts (MRC-5, typed B*07:02, 44:02, and WI-38, typed B*08:01, 58:01). Each dose of vaccine used for injection is known to contain protein components of fibroblasts including HLA. Most likely rapid de novo DSA development is due to booster effect produced by five exposures to mismatched B locus alleles which share the following epitopes: 70IAQ, 65QIA, 65QIA+76esn, 69aa+80n, and 163ew+73te. The later three consist of paired non-self and self eplets. Although likelihood of bystander effect produced by multiple vaccinations is low its impact cannot be ruled out.

The Isolation, Differentiation, and Quantification of Human Antibody-secreting B Cells from Blood: ELISpot as a Functional Readout of Humoral Immunity

The hallmark of humoral immunity is to generate functional ASCs, which synthesize and secrete Abs specific to an antigen (Ag), such as a pathogen, and are used for host defense. For the quantitative determination of the functional status of the humoral immune response of an individual, both serum Abs and circulating ASCs are commonly measured as functional readouts. In humans, peripheral blood is the most convenient and readily accessible sample that can be used for the determination of the humoral immune response elicited by host B cells. Distinct B-cell subsets, including ASCs, can be isolated directly from peripheral blood via selection with lineage-specific Ab-conjugated microbeads or via cell sorting with flow cytometry. Moreover, purified naïve and memory B cells can be activated and differentiated into ASCs in culture. The functional activities of ASCs to contribute to Ab secretion can be quantified by ELISpot, which is an assay that converges enzyme-linked immunoabsorbance assay (ELISA) and western blotting technologies to enable the enumeration of individual ASCs at the single-cell level. In practice, the ELISpot assay has been increasingly used to evaluate vaccine efficacy because of the ease of handling of a large number of blood samples. The methods of isolating human B cells from peripheral blood, the differentiation of B cells into ASCs in vitro, and the employment of ELISpot for the quantification of total IgM- and IgG-ASCs will be described here.

Regulation and Maintenance of an Adoptive T-Cell Dependent Memory B Cell Pool

We investigated the ability of monoclonal B cells to restore primary and secondary T-cell dependent antibody responses in adoptive immune-deficient hosts. Priming induced B cell activation and expansion, AID expression, antibody production and the generation of IgM⁺IgG^- and IgM^-IgG⁺ antigen-experienced B-cell subsets that persisted in the lymphopenic environment by cell division. Upon secondary transfer and recall the IgM^-IgG⁺ cells responded by the production of antigen-specific IgG while the IgM⁺ memory cells secreted mainly IgM and little IgG, but generated new B cells expressing germinal center markers. The recall responses were more efficient if the antigenic boost was delayed suggesting that a period of adaptation is necessary before the transferred cells are able to respond. Overall these findings indicate that reconstitution of a functional and complete memory pool requires transfer of all different antigen-experienced B cell subsets. We also found that the size of the memory B cell pool did not rely on the number of the responding naïve B cells, suggesting autonomous homeostatic controls for naïve and memory B cells. By reconstituting a stable memory B cell pool in immune-deficient hosts using a monoclonal high-affinity B cell population we demonstrate the potential value of B cell adoptive immunotherapy.

Impact of tofacitinib treatment on human B-cells in vitro and in vivo

B-cells are pivotal to the pathogenesis of rheumatoid arthritis and tofacitinib, a JAK inhibitor, is effective and safe in its treatment. Tofacitinib interferes with signal transduction via cytokine receptors using the common γ-chain. Despite extensive data on T-lymphocytes, the impact of tofacitinib on B-lymphocytes is poorly understood. In this study we assessed the effect of tofacitinib on B-lymphocyte differentiation and function. Tofacitinib treatment strongly impaired in vitro plasmablast development, immunoglobulin secretion and induction of B-cell fate determining transcription factors, Blimp-1, Xbp-1, and IRF-4, in naïve B-cells. Interestingly, class switch and activation-induced cytidine deaminase (AICDA) induction was only slightly reduced in activated naïve B-cells. The effect of tofacitinib on plasmablast formation, immunoglobulin secretion and proliferation was less profound, when peripheral blood B-cells, including not only naïve but also memory B-cells, were stimulated. In line with these in vitro results, the relative distribution of B-cell populations remained stable in tofacitinib treated patients. Nevertheless, a temporary increase in absolute B-cell numbers was observed 6-8 weeks after start of treatment. In addition, B-cells isolated from tofacitinib treated patients responded rapidly to in vitro activation. We demonstrate that tofacitinib has a direct impact on human naïve B-lymphocytes, independently from its effect on T-lymphocytes, by impairing their development into plasmablasts and immunoglobulin secretion. The major effect of tofacitinib on naïve B-lymphocyte development points to the potential inability of tofacitinib-treated patients to respond to novel antigens, and suggests planning vaccination strategies prior to tofacitinib treatment.

Low hemagglutinin antigen dose influenza vaccines adjuvanted with AS03 alter the long-term immune responses in BALB/c mice

We investigated the long-term immune profiles of dose-sparing, AS03-adjuvanted vaccines compared to a traditional high-dose, unadjuvated influenza vaccine formulation. BALB/c mice received 2 IM injections of influenza A/Uruguay/716/2007 (H3N2) split vaccine antigen: high-dose (HD) (3 µg hemagglutinin (HA)/dose) or low-dose (LD) formulations (0.03 µg or 0.003 µg HA) with AS03 and were followed to 34 weeks post-boost (pb). We examined serologic responses, spleen and bone marrow (BM) HA-specific antibody-secreting cells (ASCs) by ELISpot, influenza-specific cytokine/chemokine production in re-stimulated splenocytes by multiplex ELISA, and antigen-specific CD4+ T cells that express cytokines (IL-2, IFNγ, TNFα and IL-5) by flow cytometry. All formulations elicited robust serum antibody titers that persisted for at least 34 weeks. The number of antigen-specific ASCs in the spleen and BM were higher in the 2 LD +AS03 groups, but despite having fewer ASCs, the average spot size in the HD-unadjuvanted group was larger at later time-points, suggesting greater antibody production per cell. Striking differences in the long-term profiles induced by the different vaccine formulations may contribute to these different ASC profiles. The HD-unadjuvanted vaccine elicited strong Th2 cytokines during the first 6 weeks pb but LD+AS03 groups generated broader, more durable responses at later timepoints. Finally, the 0.03 µg HA+AS03 group generated the greatest number of antigen-specific CD4+ T cells and the highest percentage of poly-functional cells that expressed 2 or more cytokines. Although all of the tested vaccines induced durable antibody responses, we show that different vaccine formulations (dose-sparing, adjuvant) generate distinct long-term immune profiles. Furthermore, our data suggest that the different profiles may be generated through unique mechanisms.

High Concentrations of Measles Neutralizing Antibodies and High-Avidity Measles IgG Accurately Identify Measles Reinfection Cases

In the United States, approximately 9% of the measles cases reported from 2012 to 2014 occurred in vaccinated individuals. Laboratory confirmation of measles in vaccinated individuals is challenging since IgM assays can give inconclusive results. Although a positive reverse transcription (RT)-PCR assay result from an appropriately timed specimen can provide confirmation, negative results may not rule out a highly suspicious case. Detection of high-avidity measles IgG in serum samples provides laboratory evidence of a past immunologic response to measles from natural infection or immunization. High concentrations of measles neutralizing antibody have been observed by plaque reduction neutralization (PRN) assays among confirmed measles cases with high-avidity IgG, referred to here as reinfection cases (RICs). In this study, we evaluated the utility of measuring levels of measles neutralizing antibody to distinguish RICs from noncases by receiver operating characteristic curve analysis. Single and paired serum samples with high-avidity measles IgG from suspected measles cases submitted to the CDC for routine surveillance were used for the analysis. The RICs were confirmed by a 4-fold rise in PRN titer or by RT-quantitative PCR (RT-qPCR) assay, while the noncases were negative by both assays. Discrimination accuracy was high with serum samples collected ≥3 days after rash onset (area under the curve, 0.953; 95% confidence interval [CI], 0.854 to 0.993). Measles neutralizing antibody concentrations of ≥40,000 mIU/ml identified RICs with 90% sensitivity (95% CI, 74 to 98%) and 100% specificity (95% CI, 82 to 100%). Therefore, when serological or RT-qPCR results are unavailable or inconclusive, suspected measles cases with high-avidity measles IgG can be confirmed as RICs by measles neutralizing antibody concentrations of ≥40,000 mIU/ml.

Somatically Hypermutated Plasmodium-Specific IgM(+) Memory B Cells Are Rapid, Plastic, Early Responders upon Malaria Rechallenge

Humoral immunity consists of pre-existing antibodies expressed by long-lived plasma cells and rapidly reactive memory B cells (MBC). Recent studies of MBC development and function after protein immunization have uncovered significant MBC heterogeneity. To clarify functional roles for distinct MBC subsets during malaria infection, we generated tetramers that identify Plasmodium-specific MBCs in both humans and mice. Long-lived murine Plasmodium-specific MBCs consisted of three populations: somatically hypermutated immunoglobulin M(+) (IgM(+)) and IgG(+) MBC subsets and an unmutated IgD(+) MBC population. Rechallenge experiments revealed that high affinity, somatically hypermutated Plasmodium-specific IgM(+) MBCs proliferated and gave rise to antibody-secreting cells that dominated the early secondary response to parasite rechallenge. IgM(+) MBCs also gave rise to T cell-dependent IgM(+) and IgG(+)B220(+)CD138(+) plasmablasts or T cell-independent B220(-)CD138(+) IgM(+) plasma cells. Thus, even in competition with IgG(+) MBCs, IgM(+) MBCs are rapid, plastic, early responders to a secondary Plasmodium rechallenge and should be targeted by vaccine strategies.

Myeloid cell leukaemia 1 has a vital role in retinoic acid-mediated protection of Toll-like receptor 9-stimulated B cells from spontaneous and DNA damage-induced apoptosis

Vitamin A is an essential anti-infective agent with pleiotropic effects on cells of the immune system. The goal of the present study was to unravel the impact of the vitamin A metabolite retinoic acid (RA) on B-cell survival related both to normal B-cell homeostasis and to the detrimental effects imposed by DNA-damaging agents. By combining RA with Toll-like receptor 9 (TLR9) ligands, we show that RA prevents spontaneous, irradiation- and doxorubicin-induced apoptosis of human B cells in an RA receptor-dependent manner. RA-mediated survival involved up-regulation of the anti-apoptotic protein myeloid cell leukemia 1 (MCL1) at the transcriptional level, and knock down of MCL1 by small interfering RNA partially reversed the effects of RA. To ensure that the combination of TLR9-ligands and RA would not promote the survival of malignant B cells, the combined effects of stimulation with RA and TLR9 ligands was assessed on cells from patients with B-cell malignancies. In contrast to the effects on normal B cells, the combination of TLR9 stimulation and RA neither enhanced the MCL1 levels nor inhibited the death of malignant B cells challenged by DNA-damaging agents. Taken together, the present results reveal a vital role of MCL1 in RA-mediated survival of normal B cells. Moreover, the findings suggest that RA in combination with TLR9 ligands might be useful adjuvants in the treatment of B-cell malignancies by selectively protecting normal and not malignant B cells from DNA-damage-induced cell death.

MALT lymphoma: A paradigm of NF-κB dysregulation

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) invariably arises from a background of chronic microbial infection and/or autoimmune disorder at diverse mucosal sites. The prolonged chronic infection and/or autoimmunity generate active immune and inflammatory responses that provide a setting for evolution and development of autoreactive B-cells, their expansion and eventual malignant transformation following acquisition of genetic changes. The immune responses also play a critical role in sustaining the growth and survival of the transformed cells as shown by complete regression of a high proportion of MALT lymphoma of the stomach, ocular adnexa and skin following anti-microbial treatment. B-cell receptor engagement by auto-antigen as well as T-cell help including both cognate interaction and bystander help via soluble ligands such as CD40L and BAFF are thought to underpin the immunological drive in the lymphoma development through activation of the canonical and non-canonical NF-κB pathway respectively. Similarly, the three MALT lymphoma associated chromosome translocations, namely t(1;14)(p22;q32)/BCL10-IGH, t(14;18)(q32;q21)/IGH-MALT1,and t(11;18)(q21;q21)/BIRC3 (API2)-MALT1, are also capable of activating both canonical and non-canonical NF-κB pathways. Furthermore, TNFAIP3 (A20) inactivation by deletion and/or mutation abolishes the auto-negative feedback to several signalling including BCR and TLR, which connect to the canonical NF-κB activation pathway. Thus, there is a considerable overlap in the molecular pathways dysregulated by immunological drive and somatic genetic changes, strongly arguing for their oncogenic cooperation in the development of MALT lymphoma.

Non-infectious environmental antigens as a trigger for the initiation of an autoimmune skin disease

Pemphigus represents a group of organ specific autoimmune blistering disorders of the skin mediated by pathogenic autoantibodies with well-defined antigenic targets. While most of these diseases are sporadic, endemic forms of disease do exist. The endemic form of pemphigus foliaceus (also known as fogo selvagem, FS) exhibits epidemiological features that suggest exposure to hematophagous insect bites are a possible precipitating factor of this autoimmune disease, and provides a unique opportunity to study how environmental factors contribute to autoimmune disease development. FS patients and healthy individuals from endemic regions show an autoreactive IgM response that starts in early childhood and becomes restricted to IgG4 autoantibodies in FS patients. In searching for triggering environmental antigens, we have found that IgG4 and IgE autoantibodies from FS patients cross-react with a salivary antigen from sand flies. The presence of these cross-reactive antibodies and antibody genetic analysis confirming that these antibodies evolve from the same naïve B cells provides compelling evidence that this non-infectious environmental antigen could be the initial target of the autoantibody response in FS. Consequently, FS serves as an ideal model to study the impact of environmental antigens in the development of autoimmune disease.

Antibody persistence after serogroup C meningococcal conjugate vaccine in children with sickle cell disease

BACKGROUND

A decline of protective antibody titers after MCC vaccine has been demonstrated in healthy children, this may be an issue of concern for risk groups. The aim of this study was to evaluate the persistence of bactericidal antibodies after MCC vaccine in sickle cell disease (SCD) patients. The type of vaccine used and booster response were also analyzed.

METHODS

SCD patients (n=141) previously immunized with MCC vaccines had blood drawn 2-8 years after the last priming dose. They were distributed according to age at primary immunization into groups: <2 years and 2-13 years and evaluated by years since vaccination (2-3, 4-5 and 6-8). Serum bactericidal antibodies with baby rabbit complement (rSBA) and serogroup C-specific IgG concentrations were measured. The correlate of protection was rSBA titer ⩾8. Subjects with rSBA <8 received a booster dose and antibody levels re-evaluated after 4-6 weeks.

RESULTS

For children primed under 2years of age rSBA titer ⩾8 was demonstrated in 53.3%, 21.7% and 35.0%, 2-3, 4-5, 6-8years, respectively, after vaccination, compared with 70.0%, 45.0% and 53.5%, respectively, for individuals primed at ages 2-13years. rSBA median titers and IgG median levels were higher in the older group. Six to eight years after vaccination the percentage of patients with rSBA titers ⩾8 was significantly higher in the group primed with MCC-TT (78.5%) compared with those primed with MCC-CRM197 [Menjugate® (33.3%) or Meningitec® (35.7%)] (p=0.033). After a booster, 98% achieved rSBA titer ⩾8.

CONCLUSION

Immunity to meningococcal serogroup C in SCD children declines rapidly after vaccination and is dependent on the age at priming. Booster doses are needed to maintain protection in SCD patients. Persistence of antibodies seems to be longer in individuals primed with MCC-TT vaccine comparing to those immunized with MCC-CRM197.