Differentiation marker-negative CD4+ T cells persist after yellow fever virus vaccination and contribute to durable memory

Factors that contribute to durable immunological memory remain incompletely understood. In our longitudinal analyses of CD4+ T cell responses to the yellow fever virus (YFV) vaccine by peptide-MHC tetramers, we unexpectedly found naïve phenotype virus-specific CD4+ T cells that persisted months to years after immunization. These Marker negative T cells (TMN) lacked CD95, CXCR3, CD11a, and CD49d surface protein expression, distinguishing them from previously discovered stem-cell memory T cells. Functionally, they resembled genuine naïve T cells upon in vitro stimulation. Single-cell TCR sequencing detected expanded clonotypes within the TMN subset and identified a shared repertoire with memory and effector T cells. T cells expressing TMN-associated TCRs were rare before vaccination, suggesting their expansion following vaccination. Longitudinal tracking of YFV-specific responses over the subsequent years revealed superior stability of the TMN subset and their association with the longevity of the overall population. The identification of these long-lived, antigen-experienced T cells may inform the design of durable T cell-based vaccines and engineered T cell therapies.

SARS-CoV-2-specific T cells in unexposed adults display broad trafficking potential and cross-react with commensal antigens

The baseline composition of T cells directly affects later response to pathogens, but the complexity of precursor states remains poorly defined. Here, we examined the baseline state of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cells in unexposed individuals. SARS-CoV-2-specific CD4+ T cells were identified in prepandemic blood samples by major histocompatibility complex (MHC) class II tetramer staining and enrichment. Our data revealed a substantial number of SARS-CoV-2-specific T cells that expressed memory phenotype markers. Integrated phenotypic analyses demonstrated diverse preexisting memory states that included cells with distinct polarization features and trafficking potential to barrier tissues. T cell clones generated from tetramer-labeled cells cross-reacted with antigens from commensal bacteria in the skin and gastrointestinal tract. Direct ex vivo tetramer staining for one spike-specific population showed a similar level of cross-reactivity to sequences from endemic coronavirus and commensal bacteria. These data highlight the complexity of precursor T cell repertoire and implicate noninfectious exposures to common microbes as a key factor that shapes human preexisting immunity to SARS-CoV-2.

[Effects of porcine acellular dermal matrix combined with human epidermal stem cells on wound healing of full-thickness skin defect in nude mice]

Objective: To explore the effects of porcine acellular dermal matrix (ADM) combined with human epidermal stem cells (ESCs) on wound healing of full-thickness skin defect in nude mice. Methods: The morphology of porcine ADM was analyzed by photograph of digital camera, the cell residues in porcine ADM were observed by hematoxylin-eosin (HE) staining, the surface structure of porcine ADM was observed by scanning electron microscope, the secondary structure of porcine ADM was analyzed by infrared spectrometer, the porcine ADM particle size was analyzed by dynamic light scattering particle size analyzer, and the porcine ADM potential was analyzed by nano-particle size potentiometer. The morphology of porcine ADM was observed by inverted fluorescence microscope when it was placed in culture medium for 30 min, 1 d, and 5 d (n=2). The porcine ADM was divided into 5 min group, 10 min group, 20 min group, 30 min group, 60 min group, and 120 min group according to the random number table (the same grouping method below) in static state at normal temperature for the corresponding time to calculate the water absorption by weighing method (n=3). Swiss white mouse embryonic fibroblasts (Fbs) were divided into blank control group (culture medium only), and 50.0 g/L ADM extract group, 37.5 g/L ADM extract group, 25.0 g/L ADM extract group, 12.5 g/L ADM extract group, and 6.5 g/L ADM extract group which were added with the corresponding final concentrations of ADM extract respectively. At post culture hour (PCH) 24, 48, and 72, the cell survival rate was detected by cell counting kit 8 and the cytotoxicity was graded (n=5). The erythrocytes of a 6-week-old male Sprague-Dawley male rat were divided into normal saline group, ultra-pure water group, and 5 mg/mL ADM extract group, 10 mg/mL ADM extract group, and 15 mg/mL ADM extract group which were treated with the corresponding final concentrations of porcine ADM extract respectively. After reaction for 3 h, the absorbance value of hemoglobin was detected by microplate reader to represent the blood compatibility of porcine ADM (n=3). ESCs were isolated and cultured from the discarded prepuce of a 6-year-old healthy boy who was treated in the Department of Urology of the First Affiliated Hospital of Army Medical University (the Third Military Medical University) in July 2020, and then identified by flow cytometry. The porcine ADM particles of composite ESC (hereinafter referred to as ESC/ADM) were constructed by mixed culture. After 3 days of culture, the composite effect of ESC/ADM was observed by HE staining and laser scanning confocal microscope. Thirty-six 7-8-week-old male non-thymic nude mice were divided into phosphate buffer solution (PBS) alone group, ADM alone group, ESC alone group, and ESC/ADM group, with 9 mice in each group, and the wound model of full-thickness skin defect was established. Immediately after injury, the wounds were treated with the corresponding reagents at one time. On post injury day (PID) 1, 7, 11, and 15, the wound healing was observed and the wound healing rate was counted (n=3). On PID 7, the epithelialization of wounds was observed by HE staining and the length of un-epithelialized wound was measured (with this and the following sample numbers of 4). On PID 11, the dermal area and collagen deposition of wounds were observed by Masson staining and the dermal area of wound section was calculated, the number of cells expressing CD49f, a specific marker of ESC, was calculated with immunofluorescence staining, the mRNA expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in ESC after wound transplantation was detected by real-time fluorescence quantitative reverse transcription polymerase chain reaction. Data were statistically analyzed with independent sample t test, one-way analysis of variance, analysis of variance for repeated measurement, and least significant difference t test. Results: The porcine ADM was white particles and composed of reticular structure, with no cells inside, disordered structure, and rough surface. The absorption peak of porcine ADM appeared at the wave numbers of 1 659, 1 549, and 1 239 cm-1, respectively. The main particle size distribution of porcine ADM in solution was 500 to 700 nm, with negative charge on the surface. The morphology of porcine ADM in static state at 30 min and on 1 and 5 d was relatively stable. The water absorption of porcine ADM remained relatively high level in static state from 30 min to 120 min. The cytotoxicity of mouse embryonic Fbs in 6.5 g/L ADM extract group, 12.5 g/L ADM extract group, and 25.0 g/L ADM extract group was grade 1 at PCH 24, and the cytotoxicity of the other groups was 0 grade at each time point. After reaction for 3 h, the absorbance value of hemoglobin of erythrocytes in ultra-pure water group was significantly higher than the values in normal saline group and 15 mg/mL ADM extract group (with t values of 8.14 and 7.96, respectively, P<0.01). After 3 days of culture, the cells of the fourth passage showed pebble-like morphology, with low expression of CD71 and high expression of CD49f, which were identified as ESCs. There was ESC attachment and growth on porcine ADM particles. On PID 1, the wound sizes of nude mice were almost the same in PBS alone group, ADM alone group, ESC alone group, and ESC/ADM group. On PID 7, 11, and 15, the wound contraction of nude mice in each group was observed, especially in ADM alone group, ESC alone group, and ESC/ADM group. On PID 7, the wound healing rates of nude mice in ESC alone group and ESC/ADM group were significantly higher than the rate in PBS alone group (with t values of 2.83 and 4.72 respectively, P<0.05 or P<0.01). On PID 11, the wound healing rate of nude mice in ESC/ADM group was significantly higher than that in PBS alone group (t=4.86, P<0.01). On PID 15, the wound healing rates of nude mice in ADM alone group, ESC alone group, and ESC/ADM group were significantly higher than the rate in PBS alone group (with t values of 2.71, 2.90, and 3.23 respectively, P<0.05). On PID 7, the length of un-epithelialized wound of nude mice in ADM alone group, ESC alone group, and ESC/ADM group was (816±85), (635±66), and (163±32) μm, respectively, which were significantly shorter than (1 199±43) μm in PBS alone group (with t values of 5.69, 10.19, and 27.54 respectively, P<0.01). On PID 11, the dermal areas of wound section of nude mice in ADM alone group, ESC alone group, and ESC/ADM group were significantly larger than the area in PBS alone group (with t values of 27.14, 5.29, and 15.90 respectively, P<0.01); the collagen production of nude mice in ADM alone group and ESC/ADM group was more obvious than that in PBS alone group, and the collagen production of nude mice in ESC alone group and PBS alone group was similar. On PID 11, in the wounds of nude mice in ESC alone group and ESC/ADM group, the cells with positive expression of CD49f were respectively 135±7 and 185±15, and the mRNA expressions of GAPDH were positive; while there were no expressions of CD49f nor mRNA of GAPDH in the wounds of nude mice in PBS alone group and ADM alone group. Conclusions: ESC/ADM particles can promote the wound healing of full-thickness skin defects in nude mice, which may be related to the improved survival rate of ESCs after transplantation and the promotion of dermal structure rearrangement and angiogenesis by ADM.

Identification of Human Antigen-Specific T Cells Using Class II MHC Tetramer Staining and Enrichment

The development of peptide-major histocompatibility complex tetramers has enabled direct characterization and enumeration of antigen-specific T cells. However, the weaker interaction between class II tetramers and CD4⁺ T cells increases the challenge of using tetramers to analyze CD4⁺ T cell responses. Here, we provide an optimized class II tetramer staining protocol with a magnetic-bead enrichment strategy for the detection and functional analyses of human antigen-specific CD4⁺ T cells. This approach enables direct sampling of lymphocytes that recognize specific peptide-MHC complexes, including rare pathogen-specific CD4⁺ T cells from unexposed individuals.

SARS-CoV-2-specific T cells in unexposed adults display broad trafficking potential and cross-react with commensal antigens

The baseline composition of T cells directly impacts later response to a pathogen, but the complexity of precursor states remains poorly defined. Here we examined the baseline state of SARS-CoV-2 specific T cells in unexposed individuals. SARS-CoV-2 specific CD4 + T cells were identified in pre-pandemic blood samples by class II peptide-MHC tetramer staining and enrichment. Our data revealed a substantial number of SARS-CoV-2 specific T cells that expressed memory phenotype markers, including memory cells with gut homing receptors. T cell clones generated from tetramer-labeled cells cross-reacted with bacterial peptides and responded to stool lysates in a MHC-dependent manner. Integrated phenotypic analyses revealed additional precursor diversity that included T cells with distinct polarized states and trafficking potential to other barrier tissues. Our findings illustrate a complex pre-existing memory pool poised for immunologic challenges and implicate non-infectious stimuli from commensal colonization as a factor that shapes pre-existing immunity.

ONE SENTENCE SUMMARY

Pre-existing immunity to SARS-CoV-2 contains a complex pool of precursor lymphocytes that include differentiated cells with broad tissue tropism and the potential to cross-react with commensal antigens.

Vaccination reshapes the virus-specific T cell repertoire in unexposed adults

We examined how baseline CD4+ T cell repertoire and precursor states impact responses to pathogen infection in humans using primary immunization with yellow fever virus (YFV) vaccine. YFV-specific T cells in unexposed individuals were identified by peptide-MHC tetramer staining and tracked pre- and post-vaccination by tetramers and TCR sequencing. A substantial number of YFV-reactive T cells expressed memory phenotype markers and contained expanded clones in the absence of exposure to YFV. After vaccination, pre-existing YFV-specific T cell populations with low clonal diversity underwent limited expansion, but rare populations with a reservoir of unexpanded TCRs generated robust responses. These altered dynamics reorganized the immunodominance hierarchy and resulted in an overall increase in higher avidity T cells. Thus, instead of further increasing the representation of dominant clones, YFV vaccination recruits rare and more responsive T cells. Our findings illustrate the impact of vaccines in prioritizing T cell responses and reveal repertoire reorganization as a key component of effective vaccination.

Decoy Receptor 3 Inhibits Monosodium Urate-Induced NLRP3 Inflammasome Activation via Reduction of Reactive Oxygen Species Production and Lysosomal Rupture

Gout is a common inflammatory arthritis caused by the deposition of monosodium urate (MSU) crystals in the joints. This activates the macrophages into a proinflammatory state by inducing NLRP3-dependent interleukin-1β (IL-1β) secretion, resulting in neutrophil recruitment. Soluble decoy receptor 3 (DcR3) is an immune modulator and can exert biological functions via decoy and non-decoy actions. Previously, we showed that DcR3 suppresses lipopolysaccharides (LPS)- and virus-induced inflammatory responses in the macrophages and promotes the macrophages into the M2 phenotype. In this study, we clarified the actions of DcR3 and its non-decoy action motif heparin sulfate proteoglycan (HSPG) binding domain (HBD) in the MSU crystal-induced NLRP3 inflammasome activation in the macrophages and in mice. In bone marrow-derived macrophages, THP-1 and U937 cells, we found that the MSU crystal-induced secretion of IL-1β and activation of NLRP3 were suppressed by both DcR3.Fc and HBD.Fc. The suppression of the MSU-induced NLRP3 inflammasome activation is accompanied by the inhibition of lysosomal rupture, mitochondrial production of the reactive oxygen species (ROS), expression of cathepsins, and activity of cathepsin B, without affecting the crystal uptake and the expression of NLRP3 or pro-IL-1β. In the air pouch mice model of gout, MSU induced less amounts of IL-1β and chemokines secretion, an increased M2/M1 macrophage ratio, and a reduction of neutrophil recruitment in DcR3-transgenic mice, which expresses DcR3 in myeloid cells. Similarly, the mice intravenously treated with DcR3.Fc or HBD.Fc displayed less inflammation response. These findings indicate that HBD of DcR3 can reduce MSU crystal-induced NLRP3 inflammasome activation via modulation of mitochondrial and lysosomal functions. Therefore, we, for the first time, demonstrate a new therapeutic potential of DcR3 for the treatment of gout.

Gold lotion from citrus peel extract ameliorates imiquimod-induced psoriasis-like dermatitis in murine

BACKGROUND

Gold lotion (GL), a natural mixed product made from the peels of six citrus fruits, has recently been identified as possessing anti-oxidative, anti-inflammatory, and immunomodulatory effects. GL has been used to protect skin against UV-induced damage, but its activity against psoriasis, a chronic autoimmune skin disease caused by dysregulation between immune cells and keratinocytes, is not known. We therefore evaluated the effect of GL on imiquimod (IMQ)-induced psoriasis-like inflammation in mice.

RESULTS

GL treatment significantly attenuated IMQ-induced psoriasis-like symptoms in mice. The inflammatory cytokines upregulated by IMQ in skin lesions were also inhibited by feeding GL. In addition, GL treatment reduced the infiltration of CD4⁺ T cells/neutrophils in skin lesions and the percentage of IL-17-/IL-22-producing T cells in lymph nodes. Furthermore, GL impaired IMQ-induced type I interferon production by plasmacytoid dendritic cells (pDCs) in vitro.

CONCLUSION

Our results indicate GL can act to suppress the initiation of psoriasis and strongly suggest that GL may have potential to be applied to the treatment of psoriasis. © 2018 Society of Chemical Industry.

FcεRI γ-Chain Negatively Modulates Dectin-1 Responses in Dendritic Cells

The inhibitory effect of immunoreceptor tyrosine-based activation motif (ITAM)-containing adapters DAP12 and FcεRI γ-chain (FcRγ) has been found in many immune functions. Herein, we have further explored the role of these adapters in C-type lectin receptors response. We identified that FcRγ, but not DAP12, could negatively regulate the Dectin-1 responses in dendritic cells (DCs). Loss of FcRγ or both DAP12 and FcRγ enhanced the maturation and cytokine production in DCs upon Dectin-1 activation compared to normal cells, whereas DCs lacking only DAP12 showed little changes. In addition, increments of T cell activation and T helper 17 polarization induced by FcRγ-deficient DCs were observed both in vitro and in vivo. Examining the Dectin-1 signaling, we revealed that the activations of several signaling molecules were augmented in FcRγ-deficient DCs stimulated with Dectin-1 ligands. Furthermore, we demonstrated that the association of phosphatases SHP-1 and PTEN with FcRγ may contribute to the negative regulation of FcRγ in Dectin-1 activation in DCs. These results extend the inhibitory effect of ITAM-containing adapters to Dectin-1 response in immune functions, even though Dectin-1 contains an ITAM-like intracellular domain. According to the role of Dectin-1 in responding to microbes and tumor cells, our finding may have applications in the development of vaccine and cancer therapy.

The adjuvant effects of high-molecule-weight polysaccharides purified from Antrodia cinnamomea on dendritic cell function and DNA vaccines

The biological activity of the edible basidiomycete Antrodia cinnamomea (AC) has been studied extensively. Many effects, such as anti-cancer, anti-inflammatory, and antioxidant activities, have been reported from either crude extracts or compounds isolated from AC. However, research addressing the function of AC in enhancing immunity is rare. The aim of the present study is to investigate the active components and the mechanism involved in the immunostimulatory effect of AC. We found that polysaccharides (PS) in the water extract of AC played a major role in dendritic cell (DC) activation, which is a critical leukocyte in initiating immune responses. We further size purified and identified that the high-molecular weight PS fraction (greater than 100 kDa) exhibited the activating effect. The AC high-molecular weight PSs (AC hmwPSs) promoted pro-inflammatory cytokine production by DCs and the maturation of DCs. In addition, DC-induced antigen-specific T cell activation and Th1 differentiation were increased by AC hmwPSs. In studying the molecular mechanism, we confirmed the activation of the MAPK and NF-κB pathways in DCs after AC hmwPSs treatment. Furthermore, we demonstrated that TLR2 and TLR4 are required for the stimulatory activity of AC hmwPSs on DCs. In a mouse tumor model, we demonstrated that AC hmwPSs enhanced the anti-tumor efficacy of the HER-2/neu DNA vaccine by facilitating specific Th1 responses. Thus, we conclude that hmwPSs are the major components of AC that stimulate DCs via the TLR2/TLR4 and NF-κB/MAPK signaling pathways. The AC hmwPSs have potential to be applied as adjuvants.