Unravelling the contribution of lymph node fibroblasts to vaccine responses.

Vaccination is one of the most effective medical interventions, saving millions of lives and reducing the morbidity of infections across the lifespan, from infancy to older age. The generation of plasma cells and memory B cells that produce high affinity class switched antibodies is central to this protection, and these cells are the ultimate output of the germinal centre response. Optimal germinal centre responses require different immune cells to interact with one another in the right place and at the right time and this delicate cellular ballet is coordinated by a network of interconnected stromal cells.

Spatial dysregulation of T follicular helper cells impairs vaccine responses in aging.

The magnitude and quality of the germinal center (GC) response decline with age, resulting in poor vaccine-induced immunity in older individuals. A functional GC requires the co-ordination of multiple cell types across time and space, in particular across its two functionally distinct compartments: the light and dark zones. In aged mice, there is CXCR4-mediated mislocalization of T follicular helper (T) cells to the dark zone and a compressed network of follicular dendritic cells (FDCs) in the light zone.

Fibroblastic reticular cells provide a supportive niche for lymph node-resident macrophages.

The lymph node (LN) is home to resident macrophage populations that are essential for immune function and homeostasis, but key factors controlling this niche are undefined. Here, we show that fibroblastic reticular cells (FRCs) are an essential component of the LN macrophage niche. Genetic ablation of FRCs caused rapid loss of macrophages and monocytes from LNs across two in vivo models.

Targeting TLR4 during vaccination boosts MAdCAM-1 lymphoid stromal cell activation and promotes the aged germinal center response.

The failure to generate enduring humoral immunity after vaccination is a hallmark of advancing age. This can be attributed to a reduction in the germinal center (GC) response, which generates long-lived antibody-secreting cells that protect against (re)infection. Despite intensive investigation, the primary cellular defect underlying impaired GCs in aging has not been identified.

Lymphoid stromal cells-more than just a highway to humoral immunity.

The generation of high-affinity long-lived antibody responses is dependent on the differentiation of plasma cells and memory B cells, which are themselves the product of the germinal centre (GC) response. The GC forms in secondary lymphoid organs in response to antigenic stimulation and is dependent on the coordinated interactions between many types of leucocytes. These leucocytes are brought together on an interconnected network of specialized lymphoid stromal cells, which provide physical and chemical guidance to immune cells that are essential for the GC response.

B Cell Diversification Is Uncoupled from SAP-Mediated Selection Forces in Chronic Germinal Centers within Peyer's Patches.

Antibodies secreted within the intestinal tract provide protection from the invasion of microbes into the host tissues. Germinal center (GC) formation in lymph nodes and spleen strictly requires SLAM-associated protein (SAP)-mediated T cell functions; however, it is not known whether this mechanism plays a similar role in mucosal-associated lymphoid tissues. Here, we find that in Peyer's patches (PPs), SAP-mediated T cell help is required for promoting B cell selection in GCs, but not for clonal diversification.

Follicular Regulatory T Cells Can Access the Germinal Center Independently of CXCR5.

The germinal center (GC) response is critical for generating high-affinity humoral immunity and immunological memory, which forms the basis of successful immunization. Control of the GC response is thought to require follicular regulatory T (Tfr) cells, a subset of suppressive Foxp3 regulatory T cells located within GCs. Relatively little is known about the exact role of Tfr cells within the GC and how they exert their suppressive function.

Embryonic FAP lymphoid tissue organizer cells generate the reticular network of adult lymph nodes.

The induction of adaptive immunity is dependent on the structural organization of LNs, which is in turn governed by the stromal cells that underpin LN architecture. Using a novel fate-mapping mouse model, we trace the developmental origin of mesenchymal LN stromal cells (mLNSCs) to a previously undescribed embryonic fibroblast activation protein-α (FAP) progenitor. FAP cells of the LN anlagen express lymphotoxin β receptor (LTβR) and vascular cell adhesion molecule (VCAM), but not intercellular adhesion molecule (ICAM), suggesting they are early mesenchymal lymphoid tissue organizer (mLTo) cells.

Magnetic Resonance Imaging Is More Sensitive Than PET for Detecting Treatment-Induced Cell Death-Dependent Changes in Glycolysis.

Metabolic imaging has been widely used to measure the early responses of tumors to treatment. Here, we assess the abilities of PET measurement of [F]FDG uptake and MRI measurement of hyperpolarized [1-C]pyruvate metabolism to detect early changes in glycolysis following treatment-induced cell death in human colorectal (Colo205) and breast adenocarcinoma (MDA-MB-231) xenografts in mice. A TRAIL agonist that binds to human but not mouse cells induced tumor-selective cell death.

FcγRIIb differentially regulates pre-immune and germinal center B cell tolerance in mouse and human.

Several tolerance checkpoints exist throughout B cell development to control autoreactive B cells and prevent the generation of pathogenic autoantibodies. FcγRIIb is an Fc receptor that inhibits B cell activation and, if defective, is associated with autoimmune disease, yet its impact on specific B cell tolerance checkpoints is unknown. Here we show that reduced expression of FcγRIIb enhances the deletion and anergy of autoreactive immature B cells, but in contrast promotes autoreactive B cell expansion in the germinal center and serum autoantibody production, even in response to exogenous, non-self antigens.

Type I interferon induces CXCL13 to support ectopic germinal center formation.

Ectopic lymphoid structures form in a wide range of inflammatory conditions, including infection, autoimmune disease, and cancer. In the context of infection, this response can be beneficial for the host: influenza A virus infection-induced pulmonary ectopic germinal centers give rise to more broadly cross-reactive antibody responses, thereby generating cross-strain protection. However, despite the ubiquity of ectopic lymphoid structures and their role in both health and disease, little is known about the mechanisms by which inflammation is able to convert a peripheral tissue into one that resembles a secondary lymphoid organ.

Mice Deficient in Nucleoporin Nup210 Develop Peripheral T Cell Alterations.

The nucleopore is an essential structure of the eukaryotic cell, regulating passage between the nucleus and cytoplasm. While individual functions of core nucleopore proteins have been identified, the role of other components, such as Nup210, are poorly defined. Here, through the use of an unbiased ENU mutagenesis screen for mutations effecting the peripheral T cell compartment, we identified a Nup210 mutation in a mouse strain with altered CD4/CD8 T cell ratios.

Stromal Cells in the Tumor Microenvironment.

The tumor microenvironment comprises a mass of heterogeneous cell types, including immune cells, endothelial cells, and fibroblasts, alongside cancer cells. It is increasingly becoming clear that the development of this support niche is critical to the continued uncontrolled growth of the cancer. The tumor microenvironment contributes to the maintenance of cancer stemness and also directly promotes angiogenesis, invasion, metastasis, and chronic inflammation.

Extrinsically derived TNF is primarily responsible for limiting antiviral CD8+ T cell response magnitude.

TNF is a pro-inflammatory cytokine produced by both lymphoid and non-lymphoid cells. As a consequence of the widespread expression of its receptors (TNFR1 and 2), TNF plays a role in many important biological processes. In the context of influenza A virus (IAV) infection, TNF has variably been implicated in mediating immunopathology as well as suppression of the immune response.

Stromal networking: cellular connections in the germinal centre.

Secondary lymphoid organs are organized into distinct zones, governed by different types of mesenchymal stromal cells. These stromal cell subsets are critical for the generation of protective humoral immunity because they direct the migration of, and interaction between, multiple immune cell types to form the germinal centre. The germinal centre response generates long-lived antibody-secreting plasma cells and memory B cells which can provide long-term protection against re-infection.

Tumor-Induced IL-6 Reprograms Host Metabolism to Suppress Anti-tumor Immunity.

In patients with cancer, the wasting syndrome, cachexia, is associated with caloric deficiency. Here, we describe tumor-induced alterations of the host metabolic response to caloric deficiency that cause intratumoral immune suppression. In pre-cachectic mice with transplanted colorectal cancer or autochthonous pancreatic ductal adenocarcinoma (PDA), we find that IL-6 reduces the hepatic ketogenic potential through suppression of PPARalpha, the transcriptional master regulator of ketogenesis.

Treg cells and CTLA-4: the ball and chain of the germinal center response.

The mechanism by which regulatory T cells control the germinal center response is unknown. In this issue of Immunity, Wing et al. (2014) and Sage et al.

Distinct epigenetic signatures delineate transcriptional programs during virus-specific CD8(+) T cell differentiation.

The molecular mechanisms that regulate the rapid transcriptional changes that occur during cytotoxic T lymphocyte (CTL) proliferation and differentiation in response to infection are poorly understood. We have utilized ChIP-seq to assess histone H3 methylation dynamics within naive, effector, and memory virus-specific T cells isolated directly ex vivo after influenza A virus infection. Our results show that within naive T cells, codeposition of the permissive H3K4me3 and repressive H3K27me3 modifications is a signature of gene loci associated with gene transcription, replication, and cellular differentiation.

CD28 expression is required after T cell priming for helper T cell responses and protective immunity to infection.

The co-stimulatory molecule CD28 is essential for activation of helper T cells. Despite this critical role, it is not known whether CD28 has functions in maintaining T cell responses following activation. To determine the role for CD28 after T cell priming, we generated a strain of mice where CD28 is removed from CD4(+) T cells after priming.

Fibroblastic reticular cells of the lymph node are required for retention of resting but not activated CD8+ T cells.

Fibroblastic reticular cells (FRCs), through their expression of CC chemokine ligand (CCL)19 and CCL21, attract and retain T cells in lymph nodes (LNs), but whether this function applies to both resting and activated T cells has not been examined. Here we describe a model for conditionally depleting FRCs from LNs based on their expression of the diphtheria toxin receptor (DTR) directed by the gene encoding fibroblast activation protein-α (FAP). As expected, depleting FAP(+) FRCs causes the loss of naïve T cells, B cells, and dendritic cells from LNs, and this loss decreases the magnitude of the B- and T-cell responses to a subsequent infection with influenza A virus.

Depletion of stromal cells expressing fibroblast activation protein-α from skeletal muscle and bone marrow results in cachexia and anemia.

Fibroblast activation protein-α (FAP) identifies stromal cells of mesenchymal origin in human cancers and chronic inflammatory lesions. In mouse models of cancer, they have been shown to be immune suppressive, but studies of their occurrence and function in normal tissues have been limited. With a transgenic mouse line permitting the bioluminescent imaging of FAP(+) cells, we find that they reside in most tissues of the adult mouse.

Defining the molecular blueprint that drives CD8(+) T cell differentiation in response to infection.

A cardinal feature of adaptive, cytotoxic T lymphocyte (CTL)-mediated immunity is the ability of naïve CTLs to undergo a program of differentiation and proliferation upon activation resulting in the acquisition of lineage-specific T cell functions and eventual establishment of immunological memory. In this review, we examine the molecular factors that shape both the acquisition and maintenance of lineage-specific effector function in virus-specific CTL during both the effector and memory phases of immunity.

Affinity thresholds for naive CD8+ CTL activation by peptides and engineered influenza A viruses.

High-avidity interactions between TCRs and peptide + class I MHC (pMHCI) epitopes drive CTL activation and expansion. Intriguing questions remain concerning the constraints determining optimal TCR/pMHCI binding. The present analysis uses the TCR transgenic OT-I model to assess how varying profiles of TCR/pMHCI avidity influence naive CTL proliferation and the acquisition of effector function following exposure to the cognate H-2K(b)/OVA(257-264) (SIINFEKL) epitope and to mutants provided as peptide or in engineered influenza A viruses.

Differentiation-dependent functional and epigenetic landscapes for cytokine genes in virus-specific CD8+ T cells.

Although the simultaneous engagement of multiple effector mechanisms is thought to characterize optimal CD8(+) T-cell immunity and facilitate pathogen clearance, the differentiation pathways leading to the acquisition and maintenance of such polyfunctional activity are not well understood. Division-dependent profiles of effector molecule expression for virus-specific T cells are analyzed here by using a combination of carboxyfluorescein succinimidyl ester dilution and intracellular cytokine staining subsequent to T-cell receptor ligation. The experiments show that, although the majority of naive CD8(+) T-cell precursors are preprogrammed to produce TNF-α soon after stimulation and a proportion make both TNF-α and IL-2, the progressive acquisition of IFN-γ expression depends on continued lymphocyte proliferation.