Sofia Tyystjärvi

Foxp3-expressing regulatory T (T _reg ) cells protect against systemic autoimmunity. However, little is known about the significance of T _reg cells in inflammation-experienced tissues. Here, we use an experimental autoimmune encephalomyelitis model and show that T _reg cells accumulate and persist in the central nervous system (CNS) long after the resolution of the bulk of the inflammatory infiltrate. CNS-specific depletion of postinflammatory T _reg cells, but not systemic depletion of T _reg cells, results in autoimmune inflammatory flares in the CNS by residual local effector T cells. Expression of the NAD-consuming ectoenzyme CD38 is crucial for the functional adaptation of postinflammatory CNS T _reg cells to a stressful microenvironment, in which access to interleukin-2 (IL-2) is limited. CD38 counteracts ADP-ribosylation of the IL-2 receptor and thus maintains its high sensitivity to IL-2. This fully functional high-affinity IL-2 receptor prevents the loss of tissue-resident antigen-specific T _reg cells. These ‘stress-tolerant’ CNS T _reg cells impede the collapse of immune homeostasis in the CNS once acute inflammation is controlled.

Myelin oligodendrocyte glycoprotein antibody–associated disease (MOGAD) is a recently defined neurological autoimmune condition. The pathogenesis of the disease remains poorly understood, and no specific therapies are currently approved. Here, a comprehensive single-cell immunophenotyping of peripheral blood mononuclear cells from two independent cohorts of patients with MOGAD revealed pronounced immune perturbations in MOGAD when compared with healthy controls and patients with multiple sclerosis. Patients with MOGAD displayed an expansion of CXCR5 ⁻ CD21 ⁻ activated naïve and double-negative B cell subsets, a feature shared with patients with systemic lupus erythematosus. In addition, we observed altered Fc gamma receptor expression in natural killer cells, monocytes, and dendritic cells. Within the T cell compartment, CXCR3 ⁺ CD4 ⁺ memory T cells were reduced in the circulation of patients with MOGAD compared with healthy controls, and this result was mirrored in a transgenic mouse model that showed retention of these cells in the inflamed central nervous system. Together, these results demonstrate profound systemic immune cell alterations in MOGAD and contribute to a better understanding of this distinct disease entity.

Neuromyelitis optica is a paradigmatic autoimmune disease of the central nervous system, in which the water-channel protein AQP4 is the target antigen¹. The immunopathology in neuromyelitis optica is largely driven by autoantibodies to AQP4². However, the T cell response that is required for the generation of these anti-AQP4 antibodies is not well understood. Here we show that B cells endogenously express AQP4 in response to activation with anti-CD40 and IL-21 and are able to present their endogenous AQP4 to T cells with an AQP4-specific T cell receptor (TCR). A population of thymic B cells emulates a CD40-stimulated B cell transcriptome, including AQP4 (in mice and humans), and efficiently purges the thymic TCR repertoire of AQP4-reactive clones. Genetic ablation of Aqp4 in B cells rescues AQP4-specific TCRs despite sufficient expression of AQP4 in medullary thymic epithelial cells, and B-cell-conditional AQP4-deficient mice are fully competent to raise AQP4-specific antibodies in productive germinal-centre responses. Thus, the negative selection of AQP4-specific thymocytes is dependent on the expression and presentation of AQP4 by thymic B cells. As AQP4 is expressed in B cells in a CD40-dependent (but not AIRE-dependent) manner, we propose that thymic B cells might tolerize against a group of germinal-centre-associated antigens, including disease-relevant autoantigens such as AQP4.

Autoreactive encephalitogenic T cells exist in the healthy immune repertoire but need a trigger to induce CNS inflammation. The underlying mechanisms remain elusive, whereby microbiota were shown to be involved in the manifestation of CNS autoimmunity. Here, we used intravital imaging to explore how microbiota affect the T cells as trigger of CNS inflammation. Encephalitogenic CD4 ⁺ T cells transduced with the calcium-sensing protein Twitch-2B showed calcium signaling with higher frequency than polyclonal T cells in the small intestinal lamina propria (LP) but not in Peyer’s patches. Interestingly, nonencephalitogenic T cells specific for OVA and LCMV also showed calcium signaling in the LP, indicating a general stimulating effect of microbiota. The observed calcium signaling was microbiota and MHC class II dependent as it was significantly reduced in germfree animals and after administration of anti-MHC class II antibody, respectively. As a consequence of T cell stimulation in the small intestine, the encephalitogenic T cells start expressing Th17-axis genes. Finally, we show the migration of CD4 ⁺ T cells from the small intestine into the CNS. In summary, our direct in vivo visualization revealed that microbiota induced T cell activation in the LP, which directed T cells to adopt a Th17-like phenotype as a trigger of CNS inflammation.

Background: The human adrenal cortex undergoes several rapid remodeling steps during its lifetime. In rodents, similar remodeling occurs postnatally in the “X-zone” layer through unknown mechanisms. Furthermore, little is known regarding the impact of thyroid hormone (TH) on adrenal glands in humans. Methods: To investigate the impact of TH on adrenal pathophysiology, we created two genetic murine models mimicking human nonautoimmune hypothyroidism and hyperthyroidism. Moreover, we analyzed serum thyrotropin (TSH) and steroid hormone concentrations in patients diagnosed with congenital hypothyroidism and premature adrenarche (PA). Results: We found that TH receptor beta-mediated hypertrophy of the X-zone significantly elevated the adrenal weights of hyperthyroid women. In the hypothyroid model, the X-zone was poorly developed in both sexes. Moreover, large reciprocal changes in the expression levels of genes that regulate adrenal cortical function were observed with both models. Unexpectedly, up- and downregulation of several genes involved in catecholamine synthesis were detected in the adrenal glands of the hypothyroid and hyperthyroid models, respectively. Furthermore, TSH and adrenal steroid concentrations correlated positively in pediatric patients with congenital hypothyroidism and PA. Conclusions: Our results revealed that congenital hypothyroidism and hyperthyroidism functionally affect adrenal gland development and related steroidogenic activity, as well as the adrenal medulla.

Multidimensional single-cell analyses of T cells have fueled the debate about whether there is extensive plasticity or ‘mixed’ priming of helper T cell subsets in vivo. Here, we developed an experimental framework to probe the idea that the site of priming in the systemic immune compartment is a determinant of helper T cell–induced immunopathology in remote organs. By site-specific in vivo labeling of antigen-specific T cells in inguinal (i) or gut draining mesenteric (m) lymph nodes, we show that i-T cells and m-T cells isolated from the inflamed central nervous system (CNS) in a model of multiple sclerosis (MS) are distinct. i-T cells were Cxcr6⁺, and m-T cells expressed P2rx7. Notably, m-T cells infiltrated white matter, while i-T cells were also recruited to gray matter. Therefore, we propose that the definition of helper T cell subsets by their site of priming may guide an advanced understanding of helper T cell biology in health and disease.

Significance: Here we report that targeting the pattern recognition receptor MARCO on macrophages within the tumor alters their polarization and in turn activate natural killer (NK) cells to kill the tumor. We describe the mechanism of action, including that NK cells are induced to use receptor-mediated killing of the cancer cells. Furthermore, we find that this type of treatment works in combination with T cell-targeted checkpoint therapies. We then transfer this finding to humans and find that similar subpopulations of human macrophages also block NK cells. Finally, we find that targeting these human macrophages with a new specific antibody that we generated can activate these to release NK cell killing, thus generating a venue for combinatory treatments for cancer.

In the testis, interstitial macrophages are thought to be derived from the yolk sac during fetal development, and later replaced by bone marrow-derived macrophages. By contrast, the peritubular macrophages have been reported to emerge first in the postnatal testis and solely represent descendants of bone marrow-derived monocytes. Here, we define new monocyte and macrophage types in the fetal and postnatal testis using high-dimensional single-cell analyses. Our results show that interstitial macrophages have a dominant contribution from fetal liver-derived precursors, while peritubular macrophages are generated already at birth from embryonic precursors. We find that bone marrow-derived monocytes do not substantially contribute to the replenishment of the testicular macrophage pool even after systemic macrophage depletion. The presence of macrophages prenatally, but not postnatally, is necessary for normal spermatogenesis. Our multifaceted data thus challenge the current paradigms in testicular macrophage biology by delineating their differentiation, homeostasis and functions.

Macrophages, which are highly diverse in different tissues, play a complex and vital role in tissue development, homeostasis, and inflammation. The origin and heterogeneity of tissue‐resident monocytes and macrophages in ovaries remains unknown. Here we identify three tissue‐resident monocyte populations and five macrophage populations in the adult ovaries using high‐dimensional single cell mass cytometry. Ontogenic analyses using cell fate mapping models and cell depletion experiments revealed the infiltration of ovaries by both yolk sac and fetal liver‐derived macrophages already during the embryonic development. Moreover, we found that both embryonic and bone marrow‐derived macrophages contribute to the distinct ovarian macrophage subpopulations in the adults. These assays also showed that fetal‐derived MHC II‐negative macrophages differentiate postnatally in the maturing ovary to MHC II‐positive cells. Our analyses further unraveled that the developmentally distinct macrophage types share overlapping distribution and scavenging function in the ovaries under homeostatic conditions. In conclusion, we report here the first comprehensive analyses of ovarian monocytes and macrophages. In addition, we show that the mechanisms controlling monocyte immigration, the phenotype of different pools of interstitial macrophages, and the interconversion capacity of fetal‐derived macrophages in ovaries are remarkably different from those seen in other tissue niches.

Endothelial cells contain several nanoscale domains such as caveolae, fenestrations and transendothelial channels, which regulate signaling and transendothelial permeability. These structures can be covered by filter-like diaphragms. A transmembrane PLVAP (plasmalemma vesicle associated protein) protein has been shown to be necessary for the formation of diaphragms. The expression, subcellular localization and fenestra-forming role of PLVAP in liver sinusoidal endothelial cells (LSEC) have remained controversial. Here we show that fenestrations in LSEC contain PLVAP-diaphragms during the fetal angiogenesis, but they lose the diaphragms at birth. Although it is thought that PLVAP only localizes to diaphragms, we found luminal localization of PLVAP in adult LSEC using several imaging techniques. Plvap-deficient mice revealed that the absence of PLVAP and diaphragms did not affect the morphology, the number of fenestrations or the overall vascular architecture in the liver sinusoids. Nevertheless, PLVAP in fetal LSEC (fenestrations with diaphragms) associated with LYVE-1 (lymphatic vessel endothelial hyaluronan receptor 1), neuropilin-1 and VEGFR2 (vascular endothelial growth factor receptor 2), whereas in the adult LSEC (fenestrations without diaphragms) these complexes disappeared. Collectively, our data show that PLVAP can be expressed on endothelial cells without diaphragms, contradict the prevailing concept that biogenesis of fenestrae would be PLVAP-dependent, and reveal previously unknown PLVAP-dependent molecular complexes in LSEC during angiogenesis.