A subpopulation of high IL-21-producing CD4(+) T cells in Peyer's Patches is induced by the microbiota and regulates germinal centers.

The production of IL-21 by T follicular helper (Tfh) cells is vital in driving the germinal centre reaction and high affinity antibody formation. However, the degree of Tfh cell heterogeneity and function is not fully understood. We used a novel IL-21eGFP reporter mouse strain to analyze the diversity and role of Tfh cells. Through the analysis of GFP expression in lymphoid organs of IL-21eGFP mice, we identified a subpopulation of GFP(+), high IL-21 producing Tfh cells present only in Peyer's Patches. GFP(+)Tfh cells were found to be polyclonal and related to GFP(-)Tfh cells of Peyer's Patches in TCR repertoire composition and overall gene expression. Studies on the mechanisms of induction of GFP(+)Tfh cells demonstrated that they required the intestinal microbiota and a diverse repertoire of CD4(+) T cells and B cells. Importantly, ablation of GFP(+) cells resulted in a reduced frequency of Peyer's Patches IgG1 and germinal center B cells in addition to small but significant shifts in gut microbiome composition. Our work highlights the diversity among IL-21 producing CD4(+) Tfh cells, and the interrelationship between the intestinal bacteria and Tfh cell responses in the gut.

A High-Dimensional Atlas of Human T Cell Diversity Reveals Tissue-Specific Trafficking and Cytokine Signatures.

Depending on the tissue microenvironment, T cells can differentiate into highly diverse subsets expressing unique trafficking receptors and cytokines. Studies of human lymphocytes have primarily focused on a limited number of parameters in blood, representing an incomplete view of the human immune system. Here, we have utilized mass cytometry to simultaneously analyze T cell trafficking and functional markers across eight different human tissues, including blood, lymphoid, and non-lymphoid tissues. These data have revealed that combinatorial expression of trafficking receptors and cytokines better defines tissue specificity. Notably, we identified numerous T helper cell subsets with overlapping cytokine expression, but only specific cytokine combinations are secreted regardless of tissue type. This indicates that T cell lineages defined in mouse models cannot be clearly distinguished in humans. Overall, our data uncover a plethora of tissue immune signatures and provide a systemic map of how T cell phenotypes are altered throughout the human body.

Biology of IgE production: IgE cell differentiation and the memory of IgE responses.

The generation of long-lived plasma cells and memory B cells producing high-affinity antibodies depends on the maturation of B cell responses in germinal centers. These processes are essential for long-lasting antibody-mediated protection against infections. IgE antibodies are important for defense against parasites and toxins and can also mediate anti-tumor immunity. However, high-affinity IgE is also the main culprit responsible for the manifestations of allergic disease, including life-threatening anaphylaxisAnaphylaxis . Thus, generation of high-affinity IgE must be tightly regulated. Recent studies of IgE B cell biology have unveiled two mechanisms that limit high-affinity IgE memory responses: First, B cells that have recently switched to IgE production are programmed to rapidly differentiate into plasma cells,Plasma cells and second, IgE germinal centerGerminal center cells are transient and highly apoptotic. Opposing these processes, we now know that germinal center-derived IgG B cells can switch to IgE production, effectively becoming IgE-producing plasma cells. In this chapter, we will discuss the unique molecular and cellular pathways involved in the generation of IgE antibodies.

Maternal antibodies or nonproductive infections confound the need for rederivation.

After rederivation of a mouse parvovirus (MPV)-contaminated transgenic mouse strain, serology and PCR testing of the surrogate dam showed it to be infected with mouse parvovirus strain 1 (MPV-1). The rederived pups (n = 3) also were MPV-positive, according to serology. Despite MPV seropositivity, fecal PCR tests of the pups were negative, as were serologic results from direct-contact sentinels. Only one rederived pup survived, and this male was bred successfully. None of its mates or progeny seroconverted to MPV. At 14.5 mo of age, the rederived male mouse was euthanized; tissues were collected and submitted for MPV testing; both serologic tests and PCR analysis of mesenteric lymph nodes were MPV-negative. One explanation for the rederived pups' MPV seropostivity is passive transfer of maternal antibodies or a nonproductive MPV infection. This case illustrates that although routine serological testing of surrogate mothers and pups is appropriate, any positive results should be further investigated by using transmissibility testing (fecal PCR or contact sentinels or both) prior to repeat rederivation.

esBAF facilitates pluripotency by conditioning the genome for LIF/STAT3 signalling and by regulating polycomb function.

Signalling by the cytokine LIF and its downstream transcription factor, STAT3, prevents differentiation of pluripotent embryonic stem cells (ESCs). This contrasts with most cell types where STAT3 signalling induces differentiation. We find that STAT3 binding across the pluripotent genome is dependent on Brg1, the ATPase subunit of a specialized chromatin remodelling complex (esBAF) found in ESCs. Brg1 is required to establish chromatin accessibility at STAT3 binding targets, preparing these sites to respond to LIF signalling. Brg1 deletion leads to rapid polycomb (PcG) binding and H3K27me3-mediated silencing of many Brg1-activated targets genome wide, including the target genes of the LIF signalling pathway. Hence, one crucial role of Brg1 in ESCs involves its ability to potentiate LIF signalling by opposing PcG. Contrary to expectations, Brg1 also facilitates PcG function at classical PcG targets, including all four Hox loci, reinforcing their repression in ESCs. Therefore, esBAF does not simply antagonize PcG. Rather, the two chromatin regulators act both antagonistically and synergistically with the common goal of supporting pluripotency.

Engineering the ABA plant stress pathway for regulation of induced proximity.

Chemically induced proximity (CIP) systems use small molecules and engineered proteins to control and study biological processes. However, small molecule-based systems for controlling protein abundance or activities have been limited by toxicity, instability, cost, and slow clearance of the small molecules in vivo. To address these problems, we modified proteins of the plant abscisic acid (ABA) stress response pathway to control the proximity of cellular proteins and showed that the system could be used to regulate transcription, signal transduction, and subcellular localization of proteins in response to exogenously applied ABA. We also showed that the ABA CIP system can be combined with other CIP systems to simultaneously control multiple processes. We found that, when given to mice, ABA was orally available and had a 4-hour half-life. These properties, along with its lack of toxicity and low cost, suggest that ABA may be well suited for therapeutic applications and as an experimental tool to control diverse cellular activities in vivo.

Loss-of-function mutations in a glutathione S-transferase suppress the prune-Killer of prune lethal interaction.

The prune gene of Drosophila melanogaster is predicted to encode a phosphodiesterase. Null alleles of prune are viable but cause an eye-color phenotype. The abnormal wing discs gene encodes a nucleoside diphosphate kinase. Killer of prune is a missense mutation in the abnormal wing discs gene. Although it has no phenotype by itself even when homozygous, Killer of prune when heterozygous causes lethality in the absence of prune gene function. A screen for suppressors of transgenic Killer of prune led to the recovery of three mutations, all of which are in the same gene. As heterozygotes these mutations are dominant suppressors of the prune-Killer of prune lethal interaction; as homozygotes these mutations cause early larval lethality and the absence of imaginal discs. These alleles are loss-of-function mutations in CG10065, a gene that is predicted to encode a protein with several zinc finger domains and glutathione S-transferase activity.