T-bet Transcription Factor Promotes Antibody-Secreting Cell Differentiation by Limiting the Inflammatory Effects of IFN-γ on B Cells.

Although viral infections elicit robust interferon-γ (IFN-γ) and long-lived antibody-secreting cell (ASC) responses, the roles for IFN-γ and IFN-γ-induced transcription factors (TFs) in ASC development are unclear. We showed that B cell intrinsic expression of IFN-γR and the IFN-γ-induced TF T-bet were required for T-helper 1 cell-induced differentiation of B cells into ASCs. IFN-γR signaling induced Blimp1 expression in B cells but also initiated an inflammatory gene program that, if not restrained, prevented ASC formation. T-bet did not affect Blimp1 upregulation in IFN-γ-activated B cells but instead regulated chromatin accessibility within the Ifng and Ifngr2 loci and repressed the IFN-γ-induced inflammatory gene program. Consistent with this, B cell intrinsic T-bet was required for formation of long-lived ASCs and secondary ASCs following viral, but not nematode, infection. Therefore, T-bet facilitates differentiation of IFN-γ-activated inflammatory effector B cells into ASCs in the setting of IFN-γ-, but not IL-4-, induced inflammatory responses.

IgM Memory Cells: First Responders in Malaria.

Following the fate of antigen-specific memory B cells has been difficult. In this issue of Immunity, Krishnamurty et al. (2016) use a novel B cell tetramer to define Plasmodium-specific memory B cells in parasite-infected mice and demonstrate that after re-infection, somatically mutated IgM(+) memory B cells function as first responders by rapidly differentiating into T-cell-dependent plasmablasts and T-cell-independent plasma cells.

Targeted massively parallel sequencing of mature lymphoid neoplasms: assessment of empirical application and diagnostic utility in routine clinical practice.

Massively parallel sequencing (MPS) has become a viable diagnostic tool to interrogate genetic profiles of numerous tumors but has yet to be routinely adopted in the setting of lymphoma. Here, we report the empirical application of a targeted 40-gene panel developed for use in mature lymphoid neoplasms (MLNs) and report our experience on over 500 cases submitted for MPS during the first year of its clinical use. MPS was applied to both fresh and fixed specimens. The most frequent diagnoses were diffuse large B-cell lymphoma (116), chronic lymphocytic leukemia/small lymphocytic lymphoma (60), marginal zone lymphoma (52), and follicular lymphoma (43), followed by a spectrum of mature T-cell neoplasms (40). Of 534 cases submitted, 471 generated reportable results in MLNs, with disease-associated variants (DAVs) detected in 241 cases (51.2%). The most frequent DAVs affected TP53 (30%), CREBBP (14%), MYD88 (14%), TNFRSF14 (10%), TNFAIP3 (10%), B2M (7%), and NOTCH2 (7%). The bulk of our findings confirm what is reported in the scientific literature. While a substantial majority of mutations did not directly impact diagnosis, MPS results were utilized to either change, refine, or facilitate the final diagnosis in ~10.8% of cases with DAVs and 5.5% of cases overall. In addition, we identified preanalytic variables that significantly affect assay performance highlighting items for specimen triage. We demonstrate the technical viability and utility of the judicious use of a targeted MPS panel that may help to establish general guidelines for specimen selection and diagnostic application in MLNs in routine clinical practice.

Activation of regulatory dendritic cells by Mertk coincides with a temporal wave of apoptosis in neonatal lungs.

Multiple mechanisms restrain inflammation in neonates, most likely to prevent tissue damage caused by overly robust immune responses against newly encountered pathogens. Here, we identify a population of pulmonary dendritic cells (DCs) that express intermediate levels of CD103 (CD103int) and appear in the lungs and lung-draining lymph nodes of mice between birth and 2 weeks of age. CD103int DCs express XCR1 and CD205 and require expression of the transcription factor BATF3 for development, suggesting that they belong to the cDC1 lineage. In addition, CD103int DCs express CCR7 constitutively and spontaneously migrate to the lung-draining lymph node, where they promote stromal cell maturation and lymph node expansion. CD103int DCs mature independently of microbial exposure and TRIF- or MyD88-dependent signaling and are transcriptionally related to efferocytic and tolerogenic DCs as well as mature, regulatory DCs. Correlating with this, CD103int DCs show limited ability to stimulate proliferation and IFN-γ production by CD8+ T cells. Moreover, CD103int DCs acquire apoptotic cells efficiently, in a process that is dependent on the expression of the TAM receptor, Mertk, which drives their homeostatic maturation. The appearance of CD103int DCs coincides with a temporal wave of apoptosis in developing lungs and explains, in part, dampened pulmonary immunity in neonatal mice. Together, these data suggest a mechanism by which DCs sense apoptotic cells at sites of noninflammatory tissue remodeling, such as tumors or the developing lungs, and limit local T cell responses.

IFNγ induces epigenetic programming of human T-bethi B cells and promotes TLR7/8 and IL-21 induced differentiation.

Although B cells expressing the IFNγR or the IFNγ-inducible transcription factor T-bet promote autoimmunity in Systemic Lupus Erythematosus (SLE)-prone mouse models, the role for IFNγ signaling in human antibody responses is unknown. We show that elevated levels of IFNγ in SLE patients correlate with expansion of the T-bet expressing IgDnegCD27negCD11c+CXCR5neg (DN2) pre-antibody secreting cell (pre-ASC) subset. We demonstrate that naïve B cells form T-bethi pre-ASCs following stimulation with either Th1 cells or with IFNγ, IL-2, anti-Ig and TLR7/8 ligand and that IL-21 dependent ASC formation is significantly enhanced by IFNγ or IFNγ-producing T cells. IFNγ promotes ASC development by synergizing with IL-2 and TLR7/8 ligands to induce genome-wide epigenetic reprogramming of B cells, which results in increased chromatin accessibility surrounding IRF4 and BLIMP1 binding motifs and epigenetic remodeling of IL21R and PRDM1 loci. Finally, we show that IFNγ signals poise B cells to differentiate by increasing their responsiveness to IL-21.

Innate IFNγ-producing B cells.

In a recent paper published in Cell Research, Yan Bao and colleagues characterize a new population of IFNγ-producing innate-like B cells that promotes innate immune responses and contributes to early pathogen control following intracellular bacterial infection.

Oxidative stress and autophagy in the regulation of lysosome-dependent neuron death.

Lysosomes critically regulate the pH-dependent catabolism of extracellular and intracellular macromolecules delivered from the endocytic/heterophagy and autophagy pathways, respectively. The importance of lysosomes to cell survival is underscored not only by their unique ability effectively to degrade metalloproteins and oxidatively damaged macromolecules, but also by the distinct potential for induction of both caspase-dependent and -independent cell death with a compromise in the integrity of lysosome function. Oxidative stress and free radical damage play a principal role in cell death induced by lysosome dysfunction and may be linked to several upstream and downstream stimuli, including alterations in the autophagy degradation pathway, inhibition of lysosome enzyme function, and lysosome membrane damage. Neurons are sensitive to lysosome dysfunction, and the contribution of oxidative stress and free radical damage to lysosome dysfunction may contribute to the etiology of neurodegenerative disease. This review provides a broad overview of lysosome function and explores the contribution of oxidative stress and autophagy to lysosome dysfunction-induced neuron death. Putative signaling pathways that either induce lysosome dysfunction or result from lysosome dysfunction or both, and the role of oxidative stress, free radical damage, and lysosome dysfunction in pediatric lysosomal storage disorders (neuronal ceroid lipofuscinoses or NCL/Batten disease) and in Alzheimer's disease are emphasized.