Gauging urban resilience in the United States during the COVID-19 pandemic via social network analysis.

Social distancing policies and other restrictive measures have demonstrated efficacy in curbing the spread of the COVID-19 pandemic. However, these interventions have concurrently led to short- and long-term alterations in social connectedness. Comprehending the transformation in intracity social interactions is imperative for facilitating post-pandemic recovery and development. In this research, we employ social network analysis (SNA) to delve into the nuances of urban resilience. Specifically, we constructed intricate networks utilizing human mobility data to represent the impact of social interactions on the structural attributes of social networks while assessing urban resilience by examining the stability features of social connectedness. Our findings disclose a diverse array of responses to social distancing policies regarding social connectedness and varied social reactions across U.S. Metropolitan Statistical Areas (MSAs). Social networks generally exhibited a shift from dense to sparse configurations during restrictive orders, followed by a transition from sparse to dense arrangements upon relaxation of said orders. Furthermore, we analyzed the alterations in social connectedness as demonstrated by network centrality, which can presumably be attributed to the rigidity of policies and the inherent qualities of the examined MSAs. Our findings contribute valuable scientific insights to support informed decision-making for post-pandemic recovery and development initiatives.

Percutaneous Penetration of Liquid Crystal Monomers (LCMs) by In Vitro Three-Dimensional Human Skin Equivalents: Possible Mechanisms and Implications for Human Dermal Exposure Risks.

Liquid crystal monomers (LCMs) are indispensable materials in liquid crystal displays, which have been recognized as emerging persistent, bioaccumulative, and toxic organic pollutants. Occupational and nonoccupational exposure risk assessment suggested that dermal exposure is the primary exposure route for LCMs. However, the bioavailability and possible mechanisms of dermal exposure to LCMs via skin absorption and penetration remain unclear. Herein, we used EpiKutis 3D-Human Skin Equivalents (3D-HSE) to quantitatively assess the percutaneous penetration of nine LCMs, which were detected in e-waste dismantling workers' hand wipes with high detection frequencies. LCMs with higher log Kow and greater molecular weight (MW) were more difficult to penetrate through the skin. Molecular docking results showed that ABCG2 (an efflux transporter) may be responsible for percutaneous penetration of LCMs. These results suggest that passive diffusion and active efflux transport may be involved in the penetration of LCMs across the skin barrier. Furthermore, the occupational dermal exposure risks evaluated based on the dermal absorption factor suggested the underestimation of the continuous LCMs' health risks via dermal previously.

CRTAM determines the CD4+ cytotoxic T lymphocyte lineage.

Naive T cells differentiate into various effector T cells, including CD4(+) helper T cell subsets and CD8(+) cytotoxic T cells (CTL). Although cytotoxic CD4(+) T cells (CD4 +: CTL) also develop from naive T cells, the mechanism of development is elusive. We found that a small fraction of CD4(+) T cells that express class I-restricted T cell-associated molecule (CRTAM) upon activation possesses the characteristics of both CD4(+) and CD8(+) T cells. CRTAM(+) CD4(+) T cells secrete IFN-γ, express CTL-related genes, such as eomesodermin (Eomes), Granzyme B, and perforin, after cultivation, and exhibit cytotoxic function, suggesting that CRTAM(+) T cells are the precursor of CD4(+)CTL. Indeed, ectopic expression of CRTAM in T cells induced the production of IFN-γ, expression of CTL-related genes, and cytotoxic activity. The induction of CD4(+)CTL and IFN-γ production requires CRTAM-mediated intracellular signaling. CRTAM(+) T cells traffic to mucosal tissues and inflammatory sites and developed into CD4(+)CTL, which are involved in mediating protection against infection as well as inducing inflammatory response, depending on the circumstances, through IFN-γ secretion and cytotoxic activity. These results reveal that CRTAM is critical to instruct the differentiation of CD4(+)CTL through the induction of Eomes and CTL-related gene.

Double-stranded RNA of intestinal commensal but not pathogenic bacteria triggers production of protective interferon-ß.

The small intestine harbors a substantial number of commensal bacteria and is sporadically invaded by pathogens, but the response to these microorganisms is fundamentally different. We identified a discriminatory sensor by using Toll-like receptor 3 (TLR3). Double-stranded RNA (dsRNA) of one major commensal species, lactic acid bacteria (LAB), triggered interferon-ß (IFN-ß) production, which protected mice from experimental colitis. The LAB-induced IFN-ß response was diminished by dsRNA digestion and treatment with endosomal inhibitors. Pathogenic bacteria contained less dsRNA and induced much less IFN-ß than LAB, and dsRNA was not involved in pathogen-induced IFN-ß induction. These results identify TLR3 as a sensor to small intestinal commensal bacteria and suggest that dsRNA in commensal bacteria contributes to anti-inflammatory and protective immune responses.

Involvement of the NLRP3 inflammasome in innate and humoral adaptive immune responses to fungal beta-glucan.

Fungal beta-glucan, such as curdlan, triggers antifungal innate immune responses as well as shaping adaptive immune responses. In this study, we identified a key pathway that couples curdlan to immune responses. Curdlan promoted the production of the proinflammatory cytokine IL-1beta by dendritic cells and macrophages through the NLRP3 inflammasome. Stimulation with Candida albicans and Saccharomyces cerevisiae also triggered the NLRP3 inflammasome-mediated IL-1beta production. In vivo, NLRP3 was required for efficient Ag-specific Ab production when curdlan was used as an adjuvant, whereas it was dispensable for the induction of Th1 and Th17 cell differentiation. Furthermore, stimulation of purified B cells with curdlan-induced CD69 up-regulation and IgM production while stimulation with other NLRP3 inflammasome activators, such as silica and aluminum salt, did not. Notably, this induction required NLRP3 but was independent of Toll-like receptor and IL-1 receptor family signaling, suggesting the presence of NLRP3-dependent and IL-1 receptor family independent mechanisms in B cells responsible for Ab responses. Collectively, these findings reveal a critical role for the NLRP3 inflammasome in the regulation of antifungal innate immune responses as well as B cell activation.

Constitutive expression of IDO by dendritic cells of mesenteric lymph nodes: functional involvement of the CTLA-4/B7 and CCL22/CCR4 interactions.

Dendritic cells (DCs) express the immunoregulatory enzyme IDO in response to certain inflammatory stimuli, but it is unclear whether DCs express this enzyme under steady-state conditions in vivo. In this study, we report that the DCs in mesenteric lymph nodes (MLNs) constitutively express functional IDO, which metabolizes tryptophan to kynurenine. In line with a previous report that regulatory T cells (Tregs) can induce IDO in DCs via the CTLA-4/B7 interaction, a substantial proportion of the MLN DCs were located in juxtaposition to Tregs, whereas this tendency was not observed for splenic DCs, which do not express IDO constitutively. When CTLA-4 was selectively deleted in Tregs, the frequency of IDO-expressing DCs in MLNs decreased significantly, confirming CTLA-4's role in IDO expression by MLN DCs. We also found that the MLN DCs produced CCL22, which can attract Tregs via CCR4, and that the phagocytosis of autologous apoptotic cells induced CCL22 expression in CCL22 mRNA-negative DCs. Mice genetically deficient in the receptor for CCL22, CCR4, showed markedly reduced IDO expression in MLN-DCs, supporting the involvement of the CCL22/CCR4 axis in IDO induction. Together with our previous observation that MLN DCs contain much intracytoplasmic cellular debris in vivo, these results indicate that reciprocal interactions between the DCs and Tregs via both B7/CTLA-4 and CCL22/CCR4 lead to IDO induction in MLN DCs, which may be initiated and/or augmented by the phagocytosis of autologous apoptotic cells by intestinal DCs. Such a mechanism may help induce the specific milieu in MLNs that is required for the induction of oral tolerance.

Poly I:C-induced activation of NK cells by CD8 alpha+ dendritic cells via the IPS-1 and TRIF-dependent pathways.

NK cells play essential roles in eliminating virally infected cells and tumor cells. Polyinosinic-polycytidylic acid (poly I:C), a double-stranded RNA analog recognized by melanoma-differentiation associated gene 5 (MDA5) and TLR3, activates NK cells in vivo. MDA5 and TLR3 signal through distinct adaptor molecules, IFN-promoter stimulator-1 (IPS-1) and Toll/IL-1R domain-containing adaptor inducing IFN-beta (TRIF), respectively. However, it remains unclear how NK cells are activated by poly I:C in vivo. In this study, we demonstrate that the IPS-1-dependent and the TRIF-dependent pathways are essential for NK cell activation to poly I:C stimulation in mice, whereas deficiency in either IPS-1 or TRIF only modestly impairs the poly I:C-induced NK cell activation. Furthermore, both IPS-1 and TRIF contributed to suppression of implanted B16 tumor growth in response to poly I:C administration via NK cell activation. Presence of IPS-1 and TRIF in dendritic cells (DCs), but not NK cells, was required for production of IFN-gamma to poly I:C in NK cells in vitro. Moreover CD8alpha(+) conventional dendritic cells (cDCs), but not CD8alpha(-) cDCs, expressed genes for type I IFNs, IL-6, and IL-12p40 in response to poly I:C stimulation, and were also responsible for inducing IFN-gamma production in NK cells. Taken together, poly I:C activates the IPS-1- and TRIF-dependent pathways in CD8alpha(+) cDCs, which in turn leads to NK cell activation.

CXC chemokine ligand 12 promotes CCR7-dependent naive T cell trafficking to lymph nodes and Peyer's patches.

A number of chemokines, including CCL21, CCL19, CXCL12, and CXCL13, are coexpressed on the lumen or basal lamina of high endothelial venules (HEVs) in lymph nodes (LNs) and Peyer's patches (PPs), consistent with the idea that they might cooperate to regulate lymphocyte trafficking into these lymphoid tissues. In this study we report that CXCL12, acting through its receptor, CXCR4, cooperates with CCR7 ligands to promote T cell trafficking across HEVs. CXCL12 enhanced the CCR7-induced chemotaxis of wild-type but not CXCR4-deficient T cells in vitro at suboptimal concentrations of a CCR7 ligand, but without affecting the expression level or ligand-binding ability of CCR7. Real-time chemotaxis analysis showed that CXCL12 substantially shortened the lag time before cell migration began in vitro, but not the migration speed of T cells responding to suboptimal CCR7 ligand concentrations. In addition, CXCL12 augmented the CCR7 ligand-driven ERK phosphorylation and actin polymerization in T cells under the same conditions. In adoptive transfer experiments, CXCL12 promoted naive T cell trafficking to LNs and PPs in wild-type but not CCR7 ligand-deficient plt/plt recipient mice; this increased T cell trafficking was associated with enhanced binding of the T cells to HEVs and their subsequent migration into the LN parenchyma. Thus, CXCL12 synergizes with CCR7 ligands to promote T cell migration by sensitizing T cells through CXCR4, thus enabling them to respond to lower concentrations of CCR7 ligands. Such concerted action of chemokines provides an additional, previously unknown mechanism for efficient lymphocyte trafficking across HEVs into LNs and PPs.

CD4+CD25+ regulatory T cells in the small intestinal lamina propria show an effector/memory phenotype.

CD4(+)CD25(+) regulatory T cells (Tregs) have been implicated in the suppression of pathogenic responses to both self- and non-self-antigens in the intestine. However, their precise properties and functions in the gut, as well as the molecular basis of their recruitment to the gut, are poorly understood. Here, we found that most of the CD4(+)CD25(+) T cells in the small intestinal lamina propria (LP) express Foxp3 and exhibit an 'effector/memory' phenotype, CD44(hi)CD45RB(lo)CD62L(-), whereas only a minority of the Foxp3(+)CD4(+)CD25(+) T cells in the spleen and mesenteric lymph nodes showed this phenotype. The Tregs in the small intestinal LP (LP-Tregs) expressed higher levels of CCR4 and CCR9 and a substantially lower level of CCR7 than the Tregs in the spleen. In vitro, the LP-Tregs showed chemotaxis to CCL25/thymus-expressed chemokine. In addition, they showed efficient chemotaxis to the CCR4 ligands, CCL17/thymus and activation-regulated chemokine and CCL22/macrophage-derived chemokine, which are abundantly expressed by dendritic cells (DCs) in the small intestinal LP. In vivo, approximately 50% of the LP-Tregs were closely associated or in direct contact with LP-DCs. These findings demonstrate that LP-Tregs are phenotypically and functionally unique and raise the possibility that they are retained in the small intestinal LP through the action of CCL17 and CCL22, which are locally produced by LP-DCs.

Detection of pathogenic intestinal bacteria by Toll-like receptor 5 on intestinal CD11c+ lamina propria cells.

Toll-like receptors (TLRs) recognize distinct microbial components and induce innate immune responses. TLR5 is triggered by bacterial flagellin. Here we generated Tlr5-/- mice and assessed TLR5 function in vivo. Unlike other TLRs, TLR5 was not expressed on conventional dendritic cells or macrophages. In contrast, TLR5 was expressed mainly on intestinal CD11c+ lamina propria cells (LPCs). CD11c+ LPCs detected pathogenic bacteria and secreted proinflammatory cytokines in a TLR5-dependent way. However, CD11c+ LPCs do not express TLR4 and did not secrete proinflammatory cytokines after exposure to a commensal bacterium. Notably, transport of pathogenic Salmonella typhimurium from the intestinal tract to mesenteric lymph nodes was impaired in Tlr5-/- mice. These data suggest that CD11c+ LPCs, via TLR5, detect and are used by pathogenic bacteria in the intestinal lumen.

CCR7 is critically important for migration of dendritic cells in intestinal lamina propria to mesenteric lymph nodes.

Although dendritic cells (DCs) located in the small intestinal lamina propria (LP-DCs) migrate to mesenteric lymph nodes (MLNs) constitutively, it is unclear which chemokines regulate their trafficking to MLNs. In this study we report that LP-DCs in unperturbed mice require CCR7 to migrate to MLNs. In vitro, LP-DCs expressing CCR7 migrated toward CCL21, although the LP-DCs appeared morphologically and phenotypically immature. In MLNs, DCs bearing the unique LP-DC phenotype (CD11chighCD8alphaintCD11blowalphaLlowbeta7high and CD11chighCD8alpha-CD11bhighalphaLlowbeta7high) were abundant in wild-type mice, but were markedly fewer in CCL19-, CCL21-Ser-deficient plt/plt mice and were almost absent in CCR7-deficient mice, indicating the critical importance of CCR7 in LP-DC trafficking to MLNs. Interestingly, CCR7+ DCs in MLNs with the unique LP-DC phenotype had numerous vacuoles containing cellular debris in the cytoplasm, although MLN-DCs themselves were poorly phagocytic, suggesting that the debris was derived from the LP, where the LP-DCs ingested apoptotic intestinal epithelial cells (IECs). Consistent with this, LP-DCs ingested IECs vigorously in vitro. By presenting IEC-associated Ag, the LP-DCs also induce T cells to produce IL-4 and IL-10. Collectively, these results strongly suggest that LP-DCs with unique immunomodulatory activities migrate to MLNs in a CCR7-dependent manner to engage in the presentation of IEC-associated Ags acquired in the LP.