The Role of XCR1 and its Ligand XCL1 in Antigen Cross-Presentation by Murine and Human Dendritic Cells

Recently, the chemokine receptor XCR1 has been found to be exclusively expressed on a subset of dendritic cell (DC) known to be involved in antigen cross-presentation. This review aims to summarize the known biology of the XCR1 receptor and its chemokine ligand XCL1, both in the mouse and the human. Further, any involvement of this receptor–ligand pair in antigen uptake, cross-presentation, and induction of innate and adaptive cytotoxic immunity is explored. The concept of antigen delivery to DC via the XCR1 receptor is discussed as a vaccination strategy for selective induction of cytotoxic immunity against certain pathogens or tumors

Mouse conventional dendritic cells can be universally classified based on the mutually exclusive expression of XCR1 and SIRPα

Since the identification of mouse dendritic cells (DC) in the early 70s, all attempts to consistently classify the identified functional DC subpopulations according to their surface molecule expression failed. In the absence of DC lineage markers, a great variety of non-congruent surface molecules were used instead. Recent advances in the understanding of the involvement of transcription factors in the differentiation of DC subpopulations, together with the identification of a lineage marker for cross-presenting DC, have now allowed to establish a consistent and unified DC classification in the mouse. We demonstrate in the present article that all conventional DC in the mouse can be universally subdivided into either XCR1+ (“cross-presenting”) DC or SIRPα+ DC, irrespective of their activation status. This advancement will greatly facilitate future work on the biology of mouse DC. We discuss this new classification in view of current DC classification systems in the mouse and the human

Structure-Function Relationship of XCL1 Used for in vivo Targeting of Antigen Into XCR1+ Dendritic Cells

XCL1 is the ligand for XCR1, a chemokine receptor uniquely expressed on cross-presenting dendritic cells (DC) in mouse and man. We are interested in establishing therapeutic vaccines based on XCL1-mediated targeting of peptides or proteins into these DC. Therefore, we have functionally analyzed various XCL1 domains in highly relevant settings in vitro and in vivo. Murine XCL1 fused to ovalbumin (XCL1-OVA) was compared to an N-terminal deletion variant lacking the first seven N-terminal amino acids and to several C-terminal (deletion) variants. Binding studies with primary XCR1+ DC revealed that the N-terminal region stabilizes the binding of XCL1 to its receptor, as is known for other chemokines. Deviating from the established paradigm for chemokines, the N-terminus does not contain critical elements for inducing chemotaxis. On the contrary, this region appears to limit the chemotactic action of XCL1 at higher concentrations. A participation of the XCL1 C-terminus in receptor binding or chemotaxis could be excluded in a series of experiments. Binding studies with apoptotic and necrotic XCR1-negative cells suggested a second function for XCL1: marking of stressed cells for uptake into cross-presenting DC. In vivo studies using CD8+ T cell proliferation and cytotoxicity as readouts confirmed the critical role of the N-terminus for antigen targeting, and excluded any involvement of the C-terminus in the uptake, processing, and presentation of the fused OVA antigen. Together, these studies provide basic data on the function of the various XCL1 domains as well as relevant information on XCL1 as an antigen carrier in therapeutic vaccines

Expression of ICOS In Vivo Defines CD4+ Effector T Cells with High Inflammatory Potential and a Strong Bias for Secretion of Interleukin 10

The studies performed to date analyzed the overall participation of the inducible costimulator (ICOS) in model diseases, but did not yield information on the nature and function of ICOS-expressing T cells in vivo. We examined ICOS+ T cells in the secondary lymphoid organs of nonmanipulated mice, in the context of an “unbiased” immune system shaped by environmental antigens. Using single cell analysis, ICOSlow cells were found to be loosely associated with the early cytokines interleukin (IL)-2, IL-3, IL-6, and interferon (IFN)-γ. ICOSmedium cells, the large majority of ICOS+ T cells in vivo, were very tightly associated with the synthesis of the T helper type 2 (Th2) cytokines IL-4, IL-5, and IL-13, and these cells exhibited potent inflammatory effects in vivo. In contrast, ICOShigh T cells were highly and selectively linked to the anti-inflammatory cytokine IL-10. Overall, these data seem to indicate that ICOS cell surface density serves as a regulatory mechanism for the release of cytokines with different immunological properties. Further in vivo functional experiments with in vitro–activated T cells strongly suggested that the ICOS+ population, although representing in vivo only around 10% of T cells bearing early or late activation markers, nevertheless encompasses virtually all effector T cells, a finding with major diagnostic and therapeutic implications

Local T/B cooperation in inflamed tissues is supported by T follicular helper-like cells

Autoimmune diseases and other inflammatory conditions are characterized by large lymphocytic tissue infiltrates in which T and B cells can be found in close contact. Here, using a murine airway inflammation model, we compare antigen-specific T and B cells in lung tissue versus lung-draining lymph node. In the lung we identify a B-cell population exhibiting a classical germinal centre phenotype without being organized into ectopic lymphoid tissue. By contrast, classical CXCR5+ Bcl-6+ T follicular helper cells are not present. Nevertheless, lung-infiltrating T cells exhibit follicular helper-like properties including the potential to provide help to naive B cells. The lung tissue is also a survival niche for memory T and B cells remaining in residual peribronchial infiltrates after resolution of inflammation. Collectively, this study shows the importance of T/B cooperation not only in lymph nodes but also in inflamed peripheral tissues for local antibody responses to infection and autoimmunity

Superior antigen cross-presentation and XCR1 expression define human CD11c+CD141+ cells as homologues of mouse CD8+ dendritic cells

In recent years, human dendritic cells (DCs) could be subdivided into CD304+ plasmacytoid DCs (pDCs) and conventional DCs (cDCs), the latter encompassing the CD1c+, CD16+, and CD141+ DC subsets. To date, the low frequency of these DCs in human blood has essentially prevented functional studies defining their specific contribution to antigen presentation. We have established a protocol for an effective isolation of pDC and cDC subsets to high purity. Using this approach, we show that CD141+ DCs are the only cells in human blood that express the chemokine receptor XCR1 and respond to the specific ligand XCL1 by Ca2+ mobilization and potent chemotaxis. More importantly, we demonstrate that CD141+ DCs excel in cross-presentation of soluble or cell-associated antigen to CD8+ T cells when directly compared with CD1c+ DCs, CD16+ DCs, and pDCs from the same donors. Both in their functional XCR1 expression and their effective processing and presentation of exogenous antigen in the context of major histocompatibility complex class I, human CD141+ DCs correspond to mouse CD8+ DCs, a subset known for superior antigen cross-presentation in vivo. These data define CD141+ DCs as professional antigen cross-presenting DCs in the human

Regelung des Blutspendewesens

Dieser Beitrag beschreibt die verschiedenen nationalen und europäischen Institutionen, Kommittees, Zulassungsbehörden und Richtlinien, die das deutsche Transfusionssystem regulieren und die für dessen Qualitäts- und Sicherheitsstandards zuständig sind. An erster Stelle steht das „Gesetz zur Regelung des Transfusionswesens (Transfusionsgesetz)” vom 1. Juli 1998. Ein weiteres Regelungselement stellen die „Richtlinien zur Blutgruppenbestimmung und Bluttransfusion (Hämotherapie)” dar, welche vom Wissenschaftlichen Beirat der Bundesärztekammer und dem Paul-Ehrlich-Institut gemeinsam herausgegeben werden. Als ein weiteres Gremium beschäftigt sich der „Arbeitskreis (AK) Blut” mit dem Stand der Technik und Wissenschaft in der Transfusionsmedizin und Hämotherapie. Kompetenzen und Zuständigkeiten der unterschiedlichen Bundes- und Landesbehörden und deren Interaktionsebenen mit den medizinischen Fachgesellschaften werden dargelegt. Schließlich werden die europäischen Organisationen und Kommittees sowohl des Europarates wie auch der Europäischen Union vorgestellt, die an der Erarbeitung europaweiter Standards und Richtlinien für die Transfusionsmedizin beteiligt sind.This article describes the various national and European institutions, committees, guidelines and regulatory bodies shaping and safeguarding the standards of the German transfusion medicine system. It refers to the content of the Transfusion Medicine Act issued in 1998 by the German parliament, the national guidelines of the German Medical Association, and the work of the „Arbeitskreis Blut”, a working party on acute issues arising in the transfusion medicine area. It covers the way the various German federal (Ministry of Health, Paul-Ehrlich-Institut, Robert Koch-Institut) and land regulatory bodies interact with experts of the various German Medical Societies to ensure a high medical standard within the transfusion medicine system. Finally, it describes the European organizations and committees, both within the Council of Europe and the European Union, which are involved in shaping European standards and guidelines in transfusion medicine

Inducible costimulator (ICOS) blockade inhibits accumulation of polyfunctional T helper 1/T helper 17 cells and mitigates autoimmune arthritis

Objectives: Inducible costimulator (ICOS) and its ligand (ICOSL) regulate T and B cell responses. Glucose-6-phosphate isomerase (G6PI)-induced arthritis requires T and B lymphocytes. It was hypothesised that blocking ICOS/ICOSL interactions ameliorates G6PI-induced arthritis and reduces G6PI-specific B and T lymphocyte responses. Methods: DBA/1 mice were injected with a blocking, non-depleting anti-ICOSL monoclonal antibodies (mAbs) during the induction or effector phase of G6PI-induced arthritis. G6PI-specific antibody responses were measured by ELISA. G6PI-specific T helper (Th) cell responses were assayed by polychromatic flow cytometry. Results: Transient blockade of ICOS/ICOSL interactions profoundly reduced the severity of G6PI-induced arthritis. ELISA and proliferation assays showed no clear ex vivo correlates of protection. Polychromatic flow cytometry revealed two major findings: the absolute number of G6PI-specific Th cells was markedly diminished in secondary lymphatic organs from mice with blocked ICOS/ICOSL interactions. Within the pool of G6PI-specific Th cells the frequency of interleukin 17 (IL17), interferon γ or tumour necrosis factor α producers or polyfunctional Th cells (expressing two or more of these cytokines) was higher in treated than in control mice. Conclusions: ICOS costimulation is not mandatory for the differentiation of Th1 or Th17 cells. Instead, the lack of ICOS costimulation results in reduced survival of G6PI-specific Th cells irrespective of their functional differentiation. This study demonstrates that a thorough examination of the quantity and the quality of antigen-specific immune responses is useful to determine ex vivo correlates of efficacy for immunomodulating treatments

Antigen Export during Liver Infection of the Malaria Parasite Augments Protective Immunity

Protective immunity against preerythrocytic malaria parasite infection is difficult to achieve. Intracellular Plasmodium parasites likely minimize antigen presentation by surface-expressed major histocompatibility complex class I (MHC-I) molecules on infected cells, yet they actively remodel their host cells by export of parasite factors. Whether exported liver-stage proteins constitute better candidates for MHC-I antigen presentation to CD8(+) T lymphocytes remains unknown. Here, we systematically characterized the contribution of protein export to the magnitude of antigen-specific T-cell responses against Plasmodium berghei liver-stage parasites in C57BL/6 mice. We generated transgenic sporozoites that secrete a truncated ovalbumin (OVA) surrogate antigen only in the presence of an amino-terminal protein export element. Immunization with live attenuated transgenic sporozoites revealed that antigen export was not critical for CD8(+) T-cell priming but enhanced CD8(+) T-cell proliferation in the liver. Upon transfer of antigen-specific CD8(+) T cells, liver-stage parasites secreting the target protein were eliminated more efficiently. We conclude that Plasmodium parasites strictly control protein export during liver infection to minimize immune recognition. Strategies that enhance the discharge of parasite proteins into infected hepatocytes could improve the efficacy of candidate preerythrocytic malaria vaccines. Importance: Vaccine development against Plasmodium parasites remains a priority in malaria research. The most advanced malaria subunit vaccine candidates contain Plasmodium surface proteins with important roles for parasite vital functions. A fundamental question is whether recognition by effector CD8(+) T cells is restricted to sporozoite surface antigens or extends to parasite proteins that are synthesized during the extensive parasite expansion phase in the liver. Using a surrogate model antigen, we found that a cytoplasmic antigen is able to induce robust protective CD8(+) T-cell responses, but protein export further enhances immunogenicity and protection. Our results show that a cytoplasmic localization does not exclude a protein's candidacy for malaria subunit vaccines and that protein secretion can enhance protective immunity