Dectin-2-dependent NKT cell activation and serotype-specific antibody production in mice immunized with pneumococcal polysaccharide vaccine.

Although thymus-independent type 2 antigens generally do not undergo Ig class switching from IgM to IgG, pneumococcal polysaccharide vaccine (PPV) induces the production of serotype-specific IgG. How this happens remains unclear, however. In the present study, PPV immunization induced production of IgG as well as IgM specific for a serotype 3-pneumococcal polysaccharide in the sera of wild-type (WT) mice, but this phenomenon was significantly reduced in Dectin-2 knockout (KO) mice. Immunization with PPV caused IL-12p40 production in WT mice, but this response was significantly reduced in Dectin-2KO mice. Likewise, immunization with PPV activated natural killer T (NKT) cells in WT mice but not in Dectin-2KO mice. Furthermore, administration of α-galactosylceramide, recombinant (r)IL-12 or rIFN-γ improved the reduced IgG levels in Dectin-2KO mice, and treatment with neutralizing anti-IFN-γ mAb resulted in the reduction of IgG synthesis in PPV-immunized WT mice. Transfer of spleen cells from PPV-immunized WT mice conferred protection against pneumococcal infection on recipient mice, whereas this effect was cancelled when the transferred spleen cells were harvested from PPV-immunized Dectin-2KO mice. These results suggest that the detection of PPV antigens via Dectin-2 triggers IL-12 production, which induces IFN-γ synthesis by NKT cells and subsequently the production of serotype-specific IgG

NKT cell activation by PPV immunization.

<p>Spleen cells were prepared from WT and Dectin-2KO mice on day 9 after PPV immunization. (<b><i>A</i></b>) The obtained cells were stained with FITC-conjugated anti-CD3, PE-conjugated anti-NK1.1, and APC-conjugated anti-CD69 mAbs. Expression of CD69 in NKT (CD3⁺NK1.1⁺), NK (CD3^-NK1.1⁺) and T (CD3⁺NK1.1^-) cells were analyzed using flow cytometer. Data are shown as the mean±SD of five mice. *, <i>p</i><0.05; <i>NS</i>, not significant compared with WT mice. (<b><i>B</i></b>) Intracellular expression of IFN-γ in NKT, NK and T cells was analyzed using flow cytometer. Cut-off lines were determined on the basis of isotype-matched control IgG profile. Representative profile of the cytokine expression in each subset is shown. (<b><i>C</i></b>) Percent of IFN-γ⁺ population in NKT cells was analyzed in each group. Data are shown as the mean±SD. Similar results were obtained in three experiments. *, <i>p</i><0.05; <i>NS</i>, not significant.</p

Effect of α-GalCer treatment on the reduced production of PPS3-specific Ab in Dectin-2KO mice.

<p>Sera were collected from WT or Dectin-2KO mice on day 14 after PPV immunization. These mice received an intraperitoneal injection of α-GalCer (1 µg/mouse) or vehicle on day 7 post-PPV immunization. Concentrations of PPS3-specific IgM and IgG in sera were measured as OD450 values at×90 and×10 dilution, respectively. Data are shown as the mean±SD of four mice. Similar results were obtained in two experiments.*, <i>p</i><0.05.</p

Bioprotective role of platelet-derived microvesicles in hypothermia:insight into the differential characteristics of peripheral and splenic platelets

Abstract Background: Most platelets are present in peripheral blood, but some are stored in the spleen. Because the tissue environments of peripheral blood vessels and the spleen are quite distinct, the properties of platelets present in each may also differ. However, no studies have addressed this difference. We previously reported that hypothermia activates splenic platelets, but not peripheral blood platelets, whose biological significance remains unknown. In this study, we focused on platelet-derived microvesicles (PDMVs) and analyzed their biological significance connected to intrasplenic platelet activation during hypothermia. Methods: C57Bl/6 mice were placed in an environment of −20 °C, and their rectal temperature was decreased to 15 °C to model hypothermia. Platelets and skeletal muscle tissue were collected and analyzed for their interactions. Results: Transcriptomic changes between splenic and peripheral platelets were greater in hypothermic mice than in normal mice. Electron microscopy and real-time RT-PCR analysis revealed that platelets activated in the spleen by hypothermia internalized transcripts, encoding tissue repairing proteins, into PDMVs and released them into the plasma. Plasma microvesicles from hypothermic mice promoted wound healing in the mouse myoblast cell line C2C12. Skeletal muscles in hypothermic mice were damaged but recovered within 24 h after rewarming. However, splenectomy delayed recovery from skeletal muscle injury after the mice were rewarmed. Conclusions: These results indicate that PDMVs released from activated platelets in the spleen play an important role in the repair of skeletal muscle damaged by hypothermia

High titers of infectious SARS-CoV-2 in corpses of patients with COVID-19

Objectives: The prolonged presence of infectious SARS-CoV-2 in deceased patients with COVID-19 has been reported. However, infectious virus titers have not been determined. Such information is important for public health, death investigation, and handling corpses. The aim of this study was to assess the level of SARS-CoV-2 infectivity in the corpses of patients with COVID-19. Methods: We collected 11 nasopharyngeal swabs and 19 lung tissue specimens from 11 autopsy cases with COVID-19 in 2021. We then investigated the viral genomic copy number by real-time reverse transcription-polymerase chain reaction and infectious titers by cell culture and virus isolation. Results: Infectious virus was present in six of 11 (55%) cases, four of 11 (36%) nasopharyngeal swabs, and nine of 19 (47%) lung specimens. The virus titers ranged from 6.00E + 01 plaque-forming units/ml to 2.09E + 06 plaque-forming units/g. In all cases in which an infectious virus was found, the time from death to discovery was within 1 day and the longest postmortem interval was 13 days. Conclusion: The corpses of patients with COVID-19 may have high titers of infectious virus after a long postmortem interval (up to 13 days). Therefore, appropriate infection control measures must be taken when handling corpses