Tineke Jorritsma

B Cell Receptor-Mediated Internalization of Salmonella: A Novel Pathway for Autonomous B Cell Activation and Antibody Production

The present paradigm is that primary B cells are nonphagocytosing cells. In this study, we demonstrate that human primary B cells are able to internalize bacteria when the bacteria are recognized by the BCR. BCR-mediated internalization of Salmonella typhimurium results in B cell differentiation and secretion of anti-Salmonella Ab by the Salmonella-specific B cells. In addition, BCR-mediated internalization leads to efficient Ag delivery to the MHC class II Ag-loading compartments, even though Salmonella remains vital intracellularly in primary B cells. Consequently, BCR-mediated bacterial uptake induces efficient CD4+ T cell help, which boosts Salmonella-specific Ab production. BCR-mediated internalization of Salmonella by B cells is superior over extracellular Ag extraction to induce rapid and specific humoral immune responses and efficiently combat infection.

Antigen-Specific B Cells Reactivate an Effective Cytotoxic T Cell Response against Phagocytosed Salmonella through Cross-Presentation

Background The eradication of facultative intracellular bacterial pathogens, like Salmonella typhi, requires the concerted action of both the humoral immune response and the cytotoxic CD8+ T cell response. Dendritic cells (DCs) are considered to orchestrate the cytotoxic CD8+ T cell response via cross-presentation of bacterial antigens onto MHC class I molecules. Cross-presentation of Salmonella by DCs however, is accompanied by the induction of apoptosis in the DCs. Besides antibody production, B cells are required to clear Salmonella infection for other unknown reasons. Methodology/Principal Findings Here we show that Salmonella-specific B cells that phagocytose Salmonella upon BCR-ligation reactivate human memory CD8+ T cells via cross-presentation yielding a Salmonella-specific cytotoxic T cell response. The reactivation of CD8+ T cells is dependent on CD4+ T cell help. Unlike the DCs, B cell-mediated cross-presentation of Salmonella does not coincide with apoptosis. Conclusions/Significance B cells form a new player in the activation of the cytotoxic effector arm of the immune response and the generation of effective adaptive immunity in Salmonella infection.

CD5 costimulation induces stable Th17 development by promoting IL-23R expression and sustained STAT3 activation

IL-17-producing CD4(+) T helper (Th17) cells are important for immunity against extracellular pathogens and in autoimmune diseases. The factors that drive Th17 development in human remain a matter of debate. Here we show that, compared with classic CD28 costimulation, alternative costimulation via the CD5 or CD6 lymphocyte receptors forms a superior pathway for human Th17-priming. In the presence of the Th17-promoting cytokines IL-1β, IL-6, IL-23, and transforming growth factor-β (TGF-β), CD5 costimulation induces more Th17 cells that produce higher amounts of IL-17, which is preceded by prolonged activation of signal transducer and activator of transcription 3 (STAT3), a key regulator in Th17 differentiation, and enhanced levels of the IL-17-associated transcription factor retinoid-related orphan receptor-γt (ROR-γt). Strikingly, these Th17-promoting signals critically depend on CD5-induced elevation of IL-23 receptor (IL-23R) expression. The present data favor the novel concept that alternative costimulation via CD5, rather than classic costimulation via CD28, primes naive T cells for stable Th17 development through promoting the expression of IL-23R.

Urinary granzyme A mRNA is a biomarker to diagnose subclinical and acute cellular rejection in kidney transplant recipients

The distinction between T-cell-mediated rejection (TCMR) and other causes of kidney transplant dysfunction such as tubular necrosis requires biopsy. Subclinical rejection (SCR), an established risk factor for chronic allograft dysfunction, can only be diagnosed by protocol biopsy. A specific non-invasive biomarker to monitor immunological graft status would facilitate diagnosis and treatment of common transplantation-related complications. To identify possible markers, we measured urinary mRNA levels of several cytolytic proteins by quantitative PCR. Our cohort of 70 renal transplant recipients had biopsy proven type I and type II TCMR, acute tubular necrosis, SCR, calcineurin inhibitor-toxicity, cytomegalovirus infection, and stable graft function with normal histology. Granzyme A (GzmA) mRNA was significantly higher in subclinical and acute cellular rejection compared to patients with stable grafts or those with tubular necrosis with 80% sensitivity and up to 100% specificity. Granzyme B and perforin mRNA levels could significantly discriminate acute rejection from stable or tubular necrosis, but were not significantly elevated during SCR. Importantly, only GzmA mRNA remained below detection limits from grafts that were stable and most with tubular necrosis. Hence, the presented data indicate that urinary GzmA mRNA levels may entail a diagnostic non-invasive biomarker to distinguish patients with subclinical and acute cellular rejection from those with tubular necrosis or stable grafts.

Detection of aberrant transcription of major histocompatibility complex class II antigen presentation genes in chronic lymphocytic leukaemia identifies HLA-DOA mRNA as a prognostic factor for survival.

In human B cells, effective major histocompatibility complex (MHC) class II‐antigen presentation depends not only on MHC class II, but also on the invariant chain (CD74 or Ii), HLA‐DM (DM) and HLA‐DO (DO), the chaperones regulating the antigen loading process of MHC class II molecules. We analysed immediate ex vivo expression of HLA‐DR (DR), CD74, DM and DO in B cell chronic lymphocytic leukaemia (B‐CLL). Real‐time reverse transcription polymerase chain reaction demonstrated a highly significant upregulation of DRA, CD74, DMB, DOA and DOB mRNA in purified malignant cells compared to B cells from healthy donors. The increased mRNA levels were not translated into enhanced protein levels but could reflect aberrant transcriptional regulation. Indeed, upregulation of DRA, DMB, DOA and DOB mRNA correlated with enhanced expression of class II transactivator (CIITA). In‐depth analysis of the various CIITA transcripts demonstrated a significant increased activity of the interferon‐γ‐inducible promoter CIITA‐PIV in B‐CLL. Comparison of the aberrant mRNA levels with clinical outcome identified DOA mRNA as a prognostic indicator for survival. Multivariate analysis revealed that the prognostic value of DOA mRNA was independent of the mutational status of the IGHV genes. Thus, aberrant transcription of DOA forms a novel and additional prognostic indicator for survival in B‐CLL.

Selective Infection of Antigen-Specific B Lymphocytes by Salmonella Mediates Bacterial Survival and Systemic Spreading of Infection

Background The bacterial pathogen Salmonella causes worldwide disease. A major route of intestinal entry involves M cells, providing access to B cell-rich Peyer’s Patches. Primary human B cells phagocytose Salmonella typhimurium upon recognition by the specific surface Ig receptor (BCR). As it is unclear how Salmonella disseminates systemically, we studied whether Salmonella can use B cells as a transport device for spreading. Methodology/Principal Findings Human primary B cells or Ramos cell line were incubated with GFP-expressing Salmonella. Intracellular survival and escape was studied in vitro by live cell imaging, flow cytometry and flow imaging. HEL-specific B cells were transferred into C57BL/6 mice and HEL-expressing Salmonella spreading in vivo was analyzed investigating mesenteric lymph nodes, spleen and blood. After phagocytosis by B cells, Salmonella survives intracellularly in a non-replicative state which is actively maintained by the B cell. Salmonella is later excreted followed by reproductive infection of other cell types. Salmonella-specific B cells thus act both as a survival niche and a reservoir for reinfection. Adoptive transfer of antigen-specific B cells before oral infection of mice showed that these B cells mediate in vivo systemic spreading of Salmonella to spleen and blood. Conclusions/Significance This is a first example of a pathogenic bacterium that abuses the antigen-specific cells of the adaptive immune system for systemic spreading for dissemination of infection.

Expression Pattern of Immune Suppressive Cytokines and Growth Factors in Oesophageal Adenocarcinoma Reveal a Tumour Immune Escape-promoting Microenvironment

Immunotherapy for solid cancers, such as oesophageal adenocarcinoma (OAC), is generally hampered by an unfavourable immunological tumour microenvironment. This prompted us to investigate the nature of the OAC environment. Biopsies of tumour and normal control tissues were collected from 17 OAC patients, and investigated using fluorescent immunohistochemistry (IHC) for the expression of cyclooxygenase‐2 (COX‐2), vascular endothelial growth factor (VEGF), transforming growth factor‐β, indoleamine 2–3 dioxygenase, CXCL3 and CXCR1, and for measuring a panel of cytokines by cytometric bead array (CBA), and for Granzyme B (GrB), Perforin and PI9 detection by semi‐quantitative PCR (QPCR). IHC showed that expression of all the above‐mentioned factors is upregulated in 80–93% of the tumours. By QPCR, the cytokine interleukin (IL)‐8 was significantly upregulated in tumour samples (P < 0.05). IL‐6, IL‐10, GrB and Perforin did not show any significant difference between normal and tumour samples, whereas PI9 levels were significantly higher in normal when compared with the tumour samples. CBA confirmed upregulation of IL‐8 and show upregulation of IL‐1β in the tumours (P < 0.05). Regarding IL‐6 and interferon (IFN)‐γ, no significant differences were observed between normal and tumour tissues. The OAC microenvironment is characterized by a lack of cytokines and factors that normally would enhance anti‐cancer responses, such as IFN‐γ and GrB, and by a high expression of several immuno‐suppressive factors, such as COX‐2, VEGF and IL‐8. For future improvement of treatment efficacy of OAC patients, it will be of importance to combine immunotherapy with immune‐modulating agents.