International immunology最新文献

Adjuvants enhance vaccine efficacy by activating innate immunity; yet, the mechanisms of nanoparticle-based adjuvants remain incompletely defined. Here, we characterize CH-100, a chitosan nanoparticle adjuvant, and its capacity to coordinate dendritic cell (DC) activation and promote adaptive immune responses. CH-100 enhances antigen uptake, upregulates co-stimulatory molecules, and elicits antigen-specific antibody and cytotoxic T lymphocytes (CTL) responses. Mechanistically, CH-100 induces mitochondrial reactive oxygen species (ROS), leading to NLRP3 inflammasome activation, although NLRP3 is not essential for the observed adaptive responses. In parallel, CH-100 triggers the STING-IRF3 pathway to induce type I interferons; STING-deficiency partially diminishes antibody and CTL responses, suggesting involvement of additional signaling. Transcriptomic analysis reveals STING-independent upregulation of genes related to Th17 differentiation, accompanied by activation of TBK1, NF-κB, and p38 pathways in DCs, ultimately promoting Th17-skewed immunity. These findings demonstrate how CH-100 engages both STING-dependent and -independent innate pathways to shape adaptive immunity, offering mechanistic insights into chitosan-based adjuvants for future vaccine development.

Hepatic stellate cells (HSCs) play a crucial role in liver fibrosis. However, the methodology to directly assess the biology of primary HSCs in human liver specimens is yet to be established. In this study, we aimed to establish a robust methodology to analyse primary HSCs in human liver specimens with flow cytometry (FCM). We first applied FCM to HSCs directly isolated from liver tissues with Nycodenz density gradients. Then, we analysed HSCs in frozen/thawed liver perfusate samples and liver tissues. We also compared the phenotype of HSCs in primary biliary cholangitis (PBC) and those in healthy counterparts. We found that HSCs were substantially smaller and less dense than normal lymphocytes in the FCM analysis. By carefully defining the FCM gating strategy, we were able to establish the approach to analyse both quiescent HSCs (qHSCs) and activated HSCs (aHSCs) in human liver specimens. Importantly, we found that co-expression of CD14 and CD56 within CD45 non-immune cells permits the detection of qHSCs, whereas CD68 and CD40 within CD45 non-immune cells were valuable for assessing aHSCs. Furthermore, we found that aHSCs in PBC upregulated the expression of multiple markers associated with antigen-presentation capacity. Our established approach with FCM will be valuable for the direct analysis of qHSCs and aHSCs with FCM in various human liver specimens. Our FCM analysis of aHSCs in PBC suggested their involvement in the local immune responses.

The COVID-19 pandemic accelerated vaccinology progress, driving rapid vaccine development for infectious and non-infectious diseases. However, challenges persist: malaria, HIV, and dengue lack fully effective vaccines, whereas influenza and tuberculosis face waning efficacy. Emerging pathogens and drug-resistant strains further highlight the need for improved vaccines, particularly those offering rapid deployment, broad immunogenicity, and durable protection against variants. Adjuvants can play a dual role in this context: as new stand-alone tools for an early response to a pandemic-aiming at the 100-day mission objective-and for prevention of antimicrobial resistance; and as traditional components enhancing the efficacy and breadth of vaccines. The understanding of their mechanisms of action and novel usage could address critical gaps in pandemic preparedness, especially for vulnerable populations like children and the elderly.

Particulate antigens (Ags) such as viruses can often induce strong B-cell responses in vivo very effectively, but the molecular determinants of this complex process remain incompletely understood. In this review, we focus on recent mechanistic insights into the earliest steps in the initiation of primary B-cell responses to viruses, gained by exploiting a new generation of model particulate Ag, synthetic virus-like structures. We also review the characteristics of the resulting short- and long-term antibody (Ab) responses in mice. These studies reveal that a repeating pattern of epitope display on a virus-sized scaffold is a fundamental biophysical feature of viruses that triggers a qualitatively distinct mode of B-cell Ag receptor (BCR) signal transduction relative to soluble Ag display, and consequently serves as a standalone danger signal for Ag-specific B-cell activation. Quantitative variation in epitope density (ED) on such scaffolds modulates the degree and quality of B-cell activation both in vitro and in vivo. The presence of internal nucleic acid (iNA) in the interior of these virus-like structures can profoundly influence the resulting Ab responses for the lifespan of immunized animals. We conclude that the ED of viral surface Ags and the iNA genomes provide two essential signals that together are sufficient for B-cell activation and Ab production during antiviral responses. We place these findings in the context of the literature, discuss implications for rational vaccine design, and highlight unanswered questions to guide future research directions.

Themis (thymocyte-expressed molecule involved in selection) is a T-cell-specific protein that is critically required for positive selection in the thymus. However, its function in T-cell receptor (TCR) responses during allergic skin inflammation remains unclear. To investigate the function of Themis in peripheral T cells, we generated tamoxifen-induced Themis conditional knockout (cKO) mice. The deletion of Themis by tamoxifen treatment significantly reduced ear swelling and CD8 T-cell infiltration induced by hapten 2,4-dinitrofluorobenzene (DNFB) challenge, which activates CD8 T cells. The CD8 T cells in the inflamed skin from Themis cKO mice showed decreased interferon gamma (IFNγ) production and T-bet and Eomes expression. Furthermore, the transgenic overexpression of Themis enhanced DNFB-induced allergic skin responses. However, Themis cKO mice showed unaltered skin inflammation induced by fluorescein isothiocyanate/dibutyl phthalate, which activates CD4 T cells. The TCR-stimulated proliferation and IFNγ production of Themis cKO naïve CD8 T cells were significantly decreased in vitro, whereas the proliferation and cytokine production of CD4 T cells were not altered. As expected, the administration of the SHP-1/2 inhibitor restored the reduced IFNγ production in Themis cKO CD8 T cells in vitro. Mice harboring mutant Themis lacking the Grb2-binding site showed a similar phenotype to Themis cKO mice, indicating that the function of Themis in peripheral CD8 T cells is dependent on Grb2 binding. Collectively, these results suggest that Themis regulates the threshold of TCR signaling in peripheral CD8 T cells, but not in CD4 T cells.

In human blood B cells exist in a variety of forms ranging from antigen inexperienced naive cells to long term memory cells, and antibody producing plasma cells. Historically the divisions between these types of cells have been defined by a few characteristic surface markers such as IgD, CD27 and CD21, but recent advances in single cell techniques such as high-parameter cytometry and single cell sequencing have revealed a greater diversity of populations. An expanding palette of markers has helped to better define B cell subsets but can be a source of confusion when overlapping cell types are identified using different sets of markers. In this review we will discuss the conflicting and overlapping phenotypic and functional identities of human circulating B cells with a particular emphasis on memory B cells. We also propose a framework in which five B cell markers; IgD, CD27, CD21, CD11c and a glycosylated isoform of CD45RB can discriminate the majority of B cell populations in human blood.

The bone tissue serves as a dynamic reservoir that accommodates diverse immune cell populations during low-energy states such as fasting. Energy-restriction and reduced metabolism induce a transient migration of naïve B cells from Peyer's patches to the bone marrow in mice, a process driven by the upregulation of Cxcl13 expression within the bone niche. However, the specific cellular source of CXCL13 and the upstream signals regulating its expression remain undefined. Our analysis identified the lineage-negative fraction of the bone as the major source of CXCL13. Single-cell RNA sequencing of these cells further demonstrated that Cxcl13 was selectively expressed by osteogenic mesenchymal stromal cells (MSCs) during fasting. Consistently, immunofluorescence imaging showed an increased frequency of these CXCL13-producing cells under fasting conditions, primarily localized within the perivascular niche. Gene ontology analysis of differentially expressed genes in these cells during fasting revealed enrichment of TGF-β and PPAR signaling. In line with this, pharmacological intervention in either the TGF-β or PPARγ signaling pathway significantly attenuated fasting-induced naïve B-cell migration and CXCL13 production in the bone. These results establish a mechanistic link between systemic metabolic cues and the bone marrow immune microenvironment. We propose that osteogenic MSCs play a vital role in orchestrating this trafficking program for naïve B cells, underscoring a dynamic crosstalk between the bone stromal cells and the immune system.

Successive mRNA vaccinations preserve SARS-CoV-2-specific T-cell immunity, but how individual CD8⁺ T-cell clones behave across repeated booster doses and breakthrough infection (BTI) remains poorly defined. We longitudinally tracked bulk CD8⁺ TCRβ repertoires and spike-specific tetramer⁺ CD8⁺ T cells in adult participants across the third and fourth vaccine doses and subsequent BTI. Each booster continued to recruit previously unexpanded "new" responder clonotypes, but both the number and summed frequency of newly engaged clones declined with successive doses. In contrast, clones first recruited by the initial prime-boost doses-particularly those expanded after dose 2-formed a durable, hierarchically dominant memory pool that persisted for more than two years yet displayed progressively attenuated recall with later boosters. BTI revealed a complementary mode of repertoire remodeling: newly engaged clones that had not responded to prior vaccinations showed the strongest, but transient, expansion, broadening the antigenic targets beyond spike. On the other hand, vaccine-induced clones showed limited recall response while sustaining their dominance in the long term. Together, these findings indicate that repeated mRNA vaccination maintains a stable pool of early-established CD8⁺ T-cell clones but progressively limits their recall capacity, whereas BTI mobilizes additional, partially distinct clonotypes that expand robustly and broaden antigenic coverage.

Development of vaccines eliciting broadly neutralizing influenza antibodies (bnAbs) is an extraordinary challenge. One hypothetical proposal is that CD4+ T cell help to rare immuno-subdominant bnAb class memory B cells is one critical factor to cause these B cells to reenter secondary germinal centers (GCs) and generate potent bnAbs. In this regard, we previously showed that the prototypic hemagglutinin stem vaccine does not contain the dominant CD4+ T cell epitope. Here, to test the above hypothesis, we examined the effects of adding a single influenza T cell epitope to the stem vaccine in an influenza pre-infected booster mouse model. We found that this fused booster vaccine efficiently recruited anti-stem memory B cells with prior GC experience into the secondary GCs in draining lymph nodes. Furthermore, these secondary GC-experienced cells evolved, thereby contributing to generation of more potent neutralizing activity towards variant viruses. Thus, our results suggest the importance of T cell help in generating potent bnAbs by recruiting rare subdominant memory B cells into secondary GCs, and have implications for vaccine design.