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BackgroundPlasmodium falciparumparasites cause malaria and co-exist in humans together with B-cells for long periods of time. Immunity is only achieved after repeated exposure. There has been a lack of methods to mimic the in vivo co-occurrence, where cells and parasites can be grown together for many days, and it has been difficult with long time in vitro studies.Methods and resultsA new method for growingP. falciparumin 5% CO2with a specially formulated culture medium is described. This knowledge was used to establish the co-culture of liveP. falciparumtogether with human B-cells in vitro for 10 days. The presence of B-cells clearly enhanced parasite growth, but less so when Transwell inserts were used (not allowing passage of cells or merozoites), showing that direct contact is advantageous. B-cells also proliferated more in presence of parasites. Symbiotic parasitic growth was verified using CESS cell-line and it showed similar results, indicating that B-cells are indeed the cells responsible for the effect. In malaria endemic areas, people often have increased levels of atypical memory B-cells in the blood, and in this assay it was demonstrated that when parasites were present there was an increase in the proportion of CD19 + CD20 + CD27 − FCRL4 + B-cells, and a contraction of classical memory B-cells. This effect was most clearly seen when direct contact between B-cells and parasites was allowed.ConclusionsThese results demonstrate thatP. falciparumand B-cells undoubtedly can affect each other when allowed to multiply together, which is valuable information for future vaccine studies.

The incidence of type 1 diabetes (T1D) is increasing at an alarming rate, particularly in young children, and a better understanding of the immune response that triggers this condition is urgently required. A consistent immune feature in many individuals is the appearance of autoantibodies against pancreatic islet antigens, and this can precede the onset of diabetes by many years. Monitoring the autoantibody response is of considerable predictive value, with seroconversion to multiple islet autoantibodies incurring a high risk of future T1D development (1), particularly if the autoantibodies are of high affinity (2). Islet autoantibodies are produced by B cells in a manner that generally requires the help of specialized CD4+ T cells. Exciting recent progress in immunology has generated a new molecular definition of the T cells that provide this help, now called follicular T helper cells (Tfh) (reviewed in ref. 3) (Fig. 1 A ). Importantly, it has been established that Tfh can give rise to a memory population that circulates in peripheral blood and can be identified on the basis of particular surface markers including CXCR5 (the chemokine receptor that attracts T cells to B-cell follicles), ICOS, and PD-1 (4). This has changed the landscape for immune monitoring in diseases characterized by autoantibody production, and elevations in Tfh have been reported in a number of autoimmune conditions including systemic lupus erythematosus, rheumatoid arthritis, and autoimmune thyroid disease (reviewed in ref. 3). It has recently …

Co-ordinated interaction between distinct cell types is a hallmark of successful immune function. A striking example of this is the carefully orchestrated cooperation between helper T cells and B cells that occurs during the initiation and fine-tuning of T-cell dependent antibody responses. While these processes have evolved to permit rapid immune defense against infection, it is becoming increasingly clear that such interactions can also underpin the development of autoimmunity. Here we discuss a selection of cellular and molecular pathways that mediate T cell/B cell collaboration and highlight how in vivo models and genome wide association studies link them with autoimmune disease. In particular, we emphasize how CTLA-4-mediated regulation of CD28 signaling controls the engagement of secondary costimulatory pathways such as ICOS and OX40, and profoundly influences the capacity of T cells to provide B cell help. While our molecular understanding of the co-operation between T cells and B cells derives from analysis of secondary lymphoid tissues, emerging evidence suggests that subtly different rules may govern the interaction of T and B cells at ectopic sites during autoimmune inflammation. Accordingly, the phenotype of the T cells providing help at these sites includes notable distinctions, despite sharing core features with T cells imparting help in secondary lymphoid tissues. Finally, we highlight the interdependence of T cell and B cell responses and suggest that a significant beneficial impact of B cell depletion in autoimmune settings may be its detrimental effect on T cells engaged in molecular conversation with B cells.

The strong genetic association between particular HLA alleles and type 1 diabetes (T1D) indicates a key role for CD4+ T cells in disease; however, the differentiation state of the responsible T cells is unclear. T cell differentiation originally was considered a dichotomy between Th1 and Th2 cells, with Th1 cells deemed culpable for autoimmune islet destruction. Now, multiple additional T cell differentiation fates are recognized with distinct roles. Here, we used a transgenic mouse model of diabetes to probe the gene expression profile of islet-specific T cells by microarray and identified a clear follicular helper T (Tfh) cell differentiation signature. Introduction of T cells with a Tfh cell phenotype from diabetic animals efficiently transferred diabetes to recipient animals. Furthermore, memory T cells from patients with T1D expressed elevated levels of Tfh cell markers, including CXCR5, ICOS, PDCD1, BCL6, and IL21. Defects in the IL-2 pathway are associated with T1D, and IL-2 inhibits Tfh cell differentiation in mice. Consistent with these previous observations, we found that IL-2 inhibited human Tfh cell differentiation and identified a relationship between IL-2 sensitivity in T cells from patients with T1D and acquisition of a Tfh cell phenotype. Together, these findings identify a Tfh cell signature in autoimmune diabetes and suggest that this population could be used as a biomarker and potentially targeted for T1D interventions.

Human B cells, the main target of Epstein-Barr virus (EBV), can display several types of latent viral protein expression, denoted 0, I, IIa, IIb, or III. Of these, only type III expression induces proliferation of cells in vitro . These latency types are present at specific stages of infection and are also characteristic of different tumor types, but their generation is not fully understood. In this study, we analyzed the role of T cells in the regulation of EBV viral latency by using humanized NOD/SCID/IL2Rγ −/− mice. Several spleens presented macroscopic tumors 4 weeks after infection. Explanted spleen B cells from some of the EBV-infected mice proliferated in vitro , but this was usually lowered when cyclosporine was added to the cultures. This suggested that the in vitro growth of EBV-infected B cells required T cell help; thus, cells other than type III cells were also present in the spleens. Quantitative PCR analysis of promoter activities specific for the different EBV latency types confirmed that in addition to type III cells, type IIa and type I cells were present in the spleen. The relative usage of the viral promoter specific for I and IIa latency types (Q promoter) was higher in CD8 + cell-depleted mice, and it was absent from CD4 + cell-depleted mice. These results indicate that CD4 + T cells are necessary for the generation/maintenance of cells with latency I/IIa in the humanized mice. CD4 + T cells contributed to this process through their CD40L expression. IMPORTANCE At primary infection with EBV, the infected B cells are proliferating and express viral proteins that have transforming potential. However, when the acute infection is resolved, in healthy individuals EBV is carried by a small fraction of B cells that express a restricted number of viral proteins unable to induce proliferation. Understanding the details of this transition is of fundamental importance. We studied this question in humanized mice by manipulating their different T cell compartments before and during infection with EBV. Our results indicate that CD4 + T cells are responsible for the switch to a nonproliferating EBV program during primary infection with EBV.

We have used humanized mice, in which human immune cells differentiate de novo from transplanted cord blood progenitor cells, to study the human immune responses to infection with Mycobacterium bovis bacillus Calmette–Guérin and Mycobacterium tuberculosis . Granulomas with a core containing giant cells, human CD68 + macrophages, and high bacilli numbers surrounded by a layer of CD3 + T cells and a fibrotic response encapsulating the lesions were observed in livers and lungs from bacillus Calmette–Guérin-infected humanized mice but not in nonhumanized infected controls. Paradoxically, humanized mice contained higher mycobacterial numbers in organs than nonhumanized controls. The enhancement of bacterial load was mediated by human CD4 + cells and associated to an increased expression of Programmed Death-1 protein and CD57 on T cells, molecules associated with inhibition and senescence. The lesions from mice depleted of CD4 + cells were scarcer, minimal, and irregular compared with those from mice depleted of CD8 + cells or nondepleted controls. Granulomas of bacillus Calmette–Guérin-infected humanized mice administered with a TNF-neutralizing TNF receptor fusion molecule preserved their structure, but contained higher levels of intracellular bacilli. Extended necrosis was observed in granulomas from M. tuberculosis - but not bacillus Calmette–Guérin-infected humanized mice. Our data indicate that humanized mice can be used as a model to study the formation and maintenance of human granuloma in tuberculosis and other infectious or noninfectious diseases.

Following infection with Epstein–Barr virus (EBV), the virus is carried for life in the memory B-cell compartment in a silent state (latency I/0). These cells do not resemble the proliferating lymphoblastoid cells (LCLs) (latency III) that are generated after infection. It is of fundamental significance to identify how the different EBV expression patterns are established in the latently infected cell. In view of the prompt activatability of CD4 + T cells in primary EBV infection, and their role in B-cell differentiation, we studied the involvement of CD4 + T cells in the regulation of EBV latency. Lymphoblastoid cell lines (LCLs) were cocultured with autologous or allogeneic CD4 + T cells. Activated T cells influenced the expression of two key viral proteins that determine the fate of the infected B cell. EBNA2 was down-regulated, whereas LMP1 was unregulated and the cells proliferated less. This was paralleled by the down-regulation of the latency III promoter (Cp). Experiments performed in the transwell system showed that this change does not require cell contact, but it is mediated by soluble factors. Neutralizing experiments proved that the up-regulation of LMP1 is, to some extent, mediated by IL21, but this cytokine was not responsible for EBNA2 down-regulation. This effect was partly mediated by soluble CD40L. We detected similar regulatory functions of T cells in in vitro-infected lymphocyte populations. In conclusion, our results revealed an additional mechanism by which CD4 + T cells can control the EBV-induced B-cell proliferation.

Natural killer (NK) cells are lymphocytes of the innate immune system that, following differentiation from CD56bright to CD56dim cells, have been thought to retain fixed functional and phenotypic properties throughout their lifespan. In contrast to this notion, we here show that CD56dim NK cells continue to differentiate. During this process, they lose expression of NKG2A, sequentially acquire inhibitory killer cell inhibitory immunoglobulin-like receptors and CD57, change their expression patterns of homing molecules, and display a gradual decline in proliferative capacity. All cellular intermediates of this process are represented in varying proportions at steady state and appear, over time, during the reconstitution of the immune system, as demonstrated in humanized mice and in patients undergoing hematopoietic stem cell transplantation. CD56dim NK-cell differentiation, and the associated functional imprint, occurs independently of NK-cell education by interactions with self–human leukocyte antigen class I ligands and is an essential part of the formation of human NK-cell repertoires.

A human islet transplant can cure patients with type 1 diabetes. A drawback of islet transplantation is the life-long immunosuppressive medication, often associated with severe side effects. Moreover, in spite of the immunosuppressive therapy, islets are lost in the majority of transplanted patients over time. An improved small animal model for studies on human islet allograft rejection mechanisms and the development of new measures for its prevention is clearly warranted. Here, we evaluated the potential of Balb/cRag2(-/-)gammac(-/-) mice carrying a human-like immune system (so-called humanized mice) as a tool for studies on the rejection of transplanted human islets. Human T cells from Balb/cRag2(-/-)gammac(-/-) mice, which as neonates had been transplanted with CD34(+) human cord blood haematopoietic stem cells (HIS mice), proliferated in response to allogeneic human dendritic cells, but failed to reject a human islet allograft transplanted to the renal subcapsular space as assessed by immunohistochemistry and analysis of human serum C-peptide levels. Histological analysis revealed that few if any T cells had migrated to the grafted tissue. These observations question the usefulness of the HIS mouse model for studies on human islet allograft rejection mechanisms and highlight the need for further improvements.

Monitoring the spread of mycobacterium in vivo using biophotonic imaging provides a fast, reliable and sensitive method to evaluate the distribution of the infection. Moreover, this technique allows for a significant reduction in the number of animals required in comparison to conventional anatomopathological studies. Here, we describe for the first time and validate the use of a luciferase-tagged recombinant Mycobacterium bovis BCG for non-invasive bioluminescent imaging of 1) bacterial dissemination in tissues, 2) the efficacy of treatment with anti-mycobacterial drugs and 3) the role of adaptive immune responses in controlling mycobacterial infection in vivo.