Rare genetic variants involved in multisystem inflammatory syndrome in children: a multicenter Brazilian cohort study.

Introduction: Despite the existing data on the Multisystem Inflammatory Syndrome in Children (MIS-C), the factors that determine these patients evolution remain elusive. Answers may lie, at least in part, in genetics. It is currently under investigation that MIS-C patients may have an underlying innate error of immunity (IEI), whether of monogenic, digenic, or even oligogenic origin. Methods: To further investigate this hypothesis, 30 patients with MIS-C were submitted to whole exome sequencing. Results: Analyses of genes associated with MIS-C, MIS-A, severe covid-19, and Kawasaki disease identified twenty-nine patients with rare potentially damaging variants (50 variants were identified in 38 different genes), including those previously described in IFNA21 and IFIH1 genes, new variants in genes previously described in MIS-C patients (KMT2D, CFB, and PRF1), and variants in genes newly associated to MIS-C such as APOL1, TNFRSF13B, and G6PD. In addition, gene ontology enrichment pointed to the involvement of thirteen major pathways, including complement system, hematopoiesis, immune system development, and type II interferon signaling, that were not yet reported in MIS-C. Discussion: These data strongly indicate that different gene families may favor MIS- C development. Larger cohort studies with healthy controls and other omics approaches, such as proteomics and RNAseq, will be precious to better understanding the disease dynamics.

SARS-CoV-2 seroprevalence and social inequalities in different subgroups of healthcare workers in Rio de Janeiro, Brazil.

BACKGROUND: COVID-19 has exacerbated health inequalities worldwide. Yet, such a perspective has not been investigated in specific healthcare workers and their resulting inclusion as a priority group for vaccination have been an important focus of political and social discussion. This study aimed at investigating whether SARS-CoV-2-seropositivity in healthcare workers in a public hospital in Rio de Janeiro, Brazil, was influenced by social determinants of health and the social vulnerability in subgroups of workers. METHODS: A serological survey was conducted in 1,154 healthcare workers in June and July 2020. The association between the serological test results for detection of IgG antibodies to SARS-CoV-2 and socioeconomic, occupational characteristics and transportation used by the workers to commute was assessed using the Pearson´s chi-square test and Cramer's V. FINDINGS: Overall, the serum prevalence for the virus in the healthcare workers was 30% (342/1141). Non-white workers (208/561) with lower income (169/396) and schooling (150/353), as well as users of the mass transportation system (157/246) showed the highest infection rates. Importantly they mostly corresponded to hospital support workers (131/324), in particular the cleaning personnel (42/70). Accordingly, income, schooling and work modality appeared as negative predictors, as ascertained by forest plot analysis. INTERPRETATIONS: The data clearly illustrate the inequality in SARS-CoV-2 infection in the Brazilian population, comprising even healthcare workers of the Brazilian unified health system.

Oral Trypanosoma cruzi Acute Infection in Mice Targets Primary Lymphoid Organs and Triggers Extramedullary Hematopoiesis.

During the acute phase of Chagas disease, Trypanosoma cruzi circulation through the bloodstream leads to high tissue parasitism in the host. In primary lymphoid organs, progenitor cell reduction paralleled transient immunosuppression. Herein we showed that acute oral infection in mice promotes diffuse parasitism in bone marrow cells at 14 and 21 days post-infection (dpi), with perivascular regions, intravascular regions, and regions near the bone being target sites of parasite replication. Phenotypic analysis of hematopoietic differentiation in the bone marrow of infected mice showed that the cell number in the tissue is decreased (lineage-negative and lineage-positive cells). Interestingly, analysis of hematopoietic branching points showed that hematopoietic stem and progenitor cells (HSPCs) were significantly increased at 14 dpi. In addition, the pool of progenitors with stem plasticity (HSC-MPP3), as well as multipotent progenitors (MPPs) such as MPP4, also showed this pattern of increase. In contrast, subsequent progenitors that arise from MPPs, such as common lymphoid progenitors (CLPs), lymphoid-primed MPPs (LMPPs), and myeloid progenitors, were not enhanced; conversely, all presented numeric decline. Annexin V staining revealed that cell death increase in the initial hematopoietic branching point probably is not linked to CLPs and that myeloid progenitors decreased at 14 and 21 dpi. In parallel, our investigation provided clues that myeloid progenitor decrease could be associated with an atypical expression of Sca-1 in this population leading to a remarkable increase on LSK-like cells at 14 dpi within the HSPC compartment. Finally, these results led us to investigate HSPC presence in the spleen as a phenomenon triggered during emergency hematopoiesis due to mobilization or expansion of these cells in extramedullary sites. Splenocyte analysis showed a progressive increase in HSPCs between 14 and 21 dpi. Altogether, our study shows that the bone marrow is a target tissue in T. cruzi orally infected mice, leading to a hematopoietic disturbance with LSK-like cell bias accounting on HSPCs possibly affecting myeloid progenitor numbers. The LMPP and CLP reduction converges with defective thymocyte development. Lastly, it is tempting to speculate that the extramedullary hematopoiesis seen in the spleen is a mechanism involved in the hematological maintenance reported during the acute phase of oral T. cruzi infection.

Integrin-directed antibody-based immunotherapy: focus on VLA-4.

One major finding of chronic inflammatory diseases of various origins is the establishment of inflammatory infiltrates, bearing different leukocyte subpopulations, including activated T lymphocytes. Integrins are among the large series of molecular interactions that have been implicated as players in both triggering and maintenance of leukocyte influx from the blood into a given organ parenchyme. Accordingly, blocking the interaction between VLA-6 integrin and laminin, experimentally abrogates heart graft rejection. Many reports have shown that VLA-4 is used by T cells to cross endothelial barriers, as well as to migrate within target tissues. In this respect, a humanized IgG4 anti-VLA-4 monoclonal antibody (specific to the α4-integrin chain of VLA-4) has been successfully applied to treat multiple sclerosis as well as inflammatory bowel disease. Anti-VLA-4 monoclonal antibody has also been applied to block transendothelial passage in other autoimmune diseases, such as rheumatoid arthritis. On this same vein is the action of such a reagent in impairing in vitro transendothial and fibronectin-driven migration of CD4+ and CD8+ T cells expressing high densities of VLA-4 from Duchenne muscular dystrophy patients, thus potentially enlarging the use of this strategy to other diseases. Yet, in a small number of patients, the use of Natalizumab has been correlated with the progressive multifocal leukoencephalopathy, a serious brain infection caused by the John Cunningham virus. This issue restricted the use of the reagent. In this respect, the development of smaller and more specific antibody reagents should be envisioned as a next-generation promising strategy.

Chronic nutritional restriction of omega-3 fatty acids induces a pro-inflammatory profile during the development of the rat visual system.

Modern western diets have been associated with a reduced proportion of dietary omega-3 fatty acids leading to decreased levels of DHA (docosahexaenoic acid) in the brain. Low DHA content has been associated with altered development of visual acuity in infants and also with an altered time course of synapse elimination and plasticity in subcortical visual nuclei in rodents. Microglia has an active role in normal developmental processes such as circuitry refinement and plasticity, and its activation status can be modulated by omega-3 (ω3) and omega-6 (ω6) essential fatty acids. In the present study, we investigated the impact of dietary restriction of DHA (ω3-), through the chronic administration of a coconut-based diet as the only fat source. This dietary protocol resulted in a reduction in DHA content in the retina and superior colliculus (SC) and in a neuroinflammatory outcome during the development of the rodent visual system. The ω3- group showed changes in microglial morphology in the retina and SC and a corresponding altered pattern of pro-inflammatory cytokine expression. Early and late fish oil protocols supplementation were able to restore DHA levels. The early supplementation also decreased neuroinflammatory markers in the visual system. The present study indicates that a chronic dietary restriction of omega-3 fatty acids and the resulting deficits in DHA content, commonly observed in Western diets, interferes with the microglial profile leading to an inflamed microenvironment which may underlie a disruption of synapse elimination, altered topographical organization, abnormal plasticity, and duration of critical periods during brain development.

Critical influence of the thymus on peripheral T cell homeostasis.

INTRODUCTION: A tight balance between regulatory CD4+Foxp3+ (Treg) and conventional CD4+Foxp3- (Tconv) T cell subsets in the peripheral compartment, maintained stable throughout most of lifetime, is essential for preserving self-tolerance along with efficient immune responses. An excess of Treg cells, described for aged individuals, may critically contribute to their reported immunodeficiency. In this work, we investigated if quantitative changes in thymus emigration may alter the Treg/Tconv homeostasis regardless of the aging status of the peripheral compartment. METHODS: We used two different protocols to modify the rate of thymus emigration: thymectomy of adult young (4-6 weeks old) mice and grafting of young thymus onto aged (18 months old) hosts. Additionally, lymphoid cells from young and aged B6 mice were intravenously transferred to B6.RAG2-/- mice. Alterations in Treg and Tconv peripheral frequencies following these protocols were investigated after 30 days by flow cytometry. RESULTS: Thymectomized young mice presented a progressive increase in the Treg cell frequency, while the grafting of a functional thymus in aged mice restored the young-like physiological Treg/Tconv proportion. Strikingly, T cells derived from young or aged splenocytes colonized the lymphopenic periphery of RAG-/- hosts to the same extent, giving rise to similarly elevated Treg cell levels irrespective of the age of the donor population. In the absence of thymus output, the Treg subset seems to survive longer, as confirmed by their lower proportion of Annexin-V+ cells. CONCLUSIONS: Our data suggest that the thymus-emigrating population, harboring an adequate proportion of Treg/Tconv lymphocytes, may be essential to keep the Treg cell balance, independently of age-related shifts intrinsic to the peripheral environment or to the T cell biology.

Laminin therapy for the promotion of muscle regeneration.

Muscle regeneration is essentially due to activation of satellite cells, which can be isolated and amplified ex vivo, thus representing good candidates for cell therapy. Accumulating data show that the local microenvironment plays a major role during muscle regeneration. In the satellite cell niche, a major extracellular matrix protein is laminin. Human myoblasts transplanted into immunodeficient mice are preferentially located in laminin-enriched areas. Additionally, laminin-111 enhances myoblast proliferation in vitro and increases expression of the α7ß1 integrin-type laminin receptor. Intramuscular injection of laminin-111 ameliorates muscular pathology in mdx mice, protecting muscle fibers from damage. Moreover, transplantation of human myoblasts with laminin-111 into Rag/mdx immunodeficient recipients improved efficacy of myoblast transplantation, increasing the number of human dystrophin-positive myofibres. Taken together, these data strongly indicate that exogenous laminin can ameliorate the regeneration process in different models of muscular dystrophies and can be instrumental for improving cell therapy aiming at repairing the degeneration/regeneration process in skeletal muscle.