Kinetics of antigen-induced phenotypic and functional maturation of human monocyte-derived dendritic cells

Dose-Related Aberrant Inhibition of Intracellular Perforin Expression by S1 Subunit of Spike Glycoprotein That Contains Receptor-Binding Domain from SARS-CoV-2

Studies had shown that severe cases of COVID-19 tend to have high viral loads and correlate with functional impairment of cytotoxic lymphocytes, and the features of cytokine storm syndrome are similar to manifestations of severe influenza that have been partially explained by suppressed perforin expression. To test the hypothesis that the spike glycoprotein from SARS-CoV-2 may inhibit the perforin expression, we determined the kinetics of immune responses of CD8+ T cells to low dose (LD) or high dose (HD) of S1 stimulation through an in vitro dendritic cell (DC)-T cell model over seven days of incubation. The cytotoxic activity and intracellular perforin expression of CD8+ T cells induced by HD-S1-presenting DCs were aberrantly lower than those induced by LD-S1-presenting DCs from day three of incubation. Discrepantly, the levels of lymphoproliferation and cytokine (interferon-γ and tumor necrosis factor-α) production induced by HD-S1-presenting DCs were significantly higher than those induced by LD-S1-presenting DCs from day four. The dose-related responses between doses of S1 and intracellular perforin expression showed a significant linear correlation with a negative slope. In conclusion, the S1 subunit may suppress the perforin expression in CD8+ T cells to decrease the cytotoxic capacity to kill spike-presenting cells in a dose-dependent manner; the persistence of antigen presentation may result in an overproduction of interferon-γ and subsequent proinflammatory cytokines. That may help explain the insufficient cytotoxicity against high quantities of viruses or highly replicated strains of SARS-CoV-2 in severe cases of COVID-19.

Chemical synthesis and immunosuppressive activity of dipalmitoyl phosphatidylinositol hexamannoside

Phosphatidylinositol mannosides (PIMs) isolated from mycobacteria have been identified as an important class of phosphoglycolipids with significant immune-modulating properties. We present here the synthesis of dipalmitoyl phosphatidylinositol hexamannoside (PIM(6)) 1 and the first reported functional biology of a synthetic PIM(6). Key steps in the synthetic protocol included the selective glycosylation of an inositol 2,6-diol with a suitably protected mannosyl donor and construction of the glycan core utilizing a [3 + 4] thio-glycosylation strategy. The target 1 was purified by reverse phase chromatography and characterized by standard spectroscopic methods, HPLC, and chemical modification by deacylation to dPIM(6). The (1)H NMR spectrum of synthetic dPIM(6) obtained from 1 matched that of dPIM(6) obtained from nature. PIM(6) (1) exhibited dendritic cell-dependent suppression of CD8(+) T cell expansion in a human mixed lymphocyte reaction consistent with the well established immunosuppressive activity of whole mycobacteria.

Low dose HIV-1 Tat improves the defective nuclear factor (NF)-kappaB activity of dendritic cells from persons with spinal cord injury

Deficits of immune function may be involved in the infections associated with spinal cord injury (SCI). Previous report showed that the impaired maturation potential of dendritic cells (DCs) contributes to immune defect in persons with SCI, especially in those with tetraplegia. To evaluate the roles of cell signaling in the impaired maturation potential of DCs, we assessed the phenotypic and functional maturation potential of DCs in 20 subjects with trauma-induced stable SCI and their neurologically intact healthy control in the presence of DC stimulators, including HIV-1 Tat protein (Tat). Our results showed the tetraplegic subjects had an impaired maturation potential of DCs. The impairment could be attributed to insufficient nuclear factor (NF)-kappaB activity. The maturation potentials and NF-kappaB activity of DCs in response to stimulators could be improved by pretreatment with Tat, although Tat did not increase DC maturation. The improvement by Tat pretreatment was inhibited by a specific NF-kappaB blocker. We concluded that HIV-1 Tat could improve the maturation potentials of DCs from tetraplegic subjects, through Tat-induced enhancement of NF-kappaB activity. These data suggest a potential therapeutic role of HIV-1 Tat in improving immune function in tetraplegic persons.

Monocyte-derived dendritic cells from chagasic patients vs healthy donors secrete differential levels of IL-10 and IL-12 when stimulated with a protein fragment of Trypanosoma cruzi heat-shock protein-70

We analyzed the effect of the truncated heat-shock protein 70 from Trypanosoma cruzi on maturation of human dendritic cells (DCs) derived from monocytes of peripheral blood mononuclear cells from healthy donors and chagasic patients. The results show that the T-HSP70 is capable of maturing human DCs inducing an increase in the expression level of the CD83, CD86 and human leukocyte antigen-DR surface markers, as well as in the secretion of interleukin (IL)-12, tumor necrosis factor-alpha (TNF-alpha) and IL-6 cytokines. Results also show the existence of a differential functional activity of matured DCs from chagasic patients vs healthy donors in response to T-HSP70 protein and to HSP-70-derived A72 peptide, as only T-HSP70-matured DCs from chagasic patients have an enhanced secretion of IL-10 and a reduced secretion of IL-12. Moreover, the addition of A72 peptide to immature DCs from chagasic patients induced an increase in the percentage of cells expressing CD83 and CD86 molecules regarding to the expression level observed by cells from healthy donors. These findings suggest that T. cruzi HSP70 protein may induce a specific maturation profile on chagasic patients' DCs, which would favor the persistence of the parasite in the human host.

Aberrant induction of regulatory activity of CD4+CD25+ T cells by dendritic cells in HIV-infected persons with amebic liver abscess

To know why HIV-1-infected persons are particularly susceptible to amebic liver abscess (ALA), we investigated the role of CD4CD25 T cells in the susceptibility of HIV-1-infected persons to this disease. Herein we show, in early stage HIV-1-infected subjects, that CD4 T-cell responses to Entamoeba histolytica antigen (EhAg) were selectively impaired, especially in those with ALA. EhAg-specific CD4 T-cell responses were normalized by depletion of CD4CD25 cells or by addition of anti-cytotoxic T lymphocyte antigen 4 (CTLA4) antibody. Regulatory activity of CD4CD25 T cells to suppress the EhAg-specific CD4 T-cell response could be induced by EhAg-primed dendritic cells (DCs) in HIV-1-infected subjects, especially in those with ALA, but not in healthy controls. Exogenous Tat-incubated DCs derived from HIV-negative subjects also could upregulate CTLA4 expression on autologous CD4CD25 T cells and selectively suppress the EhAg-specific CD4 T-cell response. The results imply an interaction of the two pathogens: HIV-1, perhaps through the effect of Tat on DCs, may upregulate EhAg-specific regulatory T-cell activity to suppress T-cell response to E. histolytica, thus increasing the susceptibility to invasive amebiasis in even early-stage HIV-1-infected persons.

Insufficient perforin expression in CD8+ T cells in response to hemagglutinin from avian influenza (H5N1) virus

Hypercytokinemia has been considered to be responsible for hemophagocytosis and multiorgan failure in severe human cases of H5N1 viral infection. In this study, we show a recombinant hemagglutinin (H5) from a H5N1 virus may suppress the perforin expression and reduce cytotoxicity of human CD8+ T cells to kill H5-bearing cells. The persistence of H5-presenting cells provides sustained stimulation and leads to a marked lymphoproliferation and IFN-gamma hyperproduction. We propose the IFN-gamma hyperproduction may explain macrophage overactivation and subsequent hypercytokinemia and hemophagocytosis in severe human cases of avian influenza.

In vitro maturation potential of monocyte-derived dendritic cells is impaired in patients with spinal cord injury: a case-control study

OBJECTIVE

To determine whether the T-cell reactivity and maturation potential of dendritic cells are impaired in subjects with spinal cord injury (SCI).

DESIGN

Cross-sectional, case-control study.

SETTING

University hospital in Taiwan.

PARTICIPANTS

Thirty male SCI subjects, including 14 with paraplegia and 16 with tetraplegia, and 30 age- and sex-matched healthy controls.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

CD4+ and CD8+ T-cell reactivity was assessed by lymphoproliferative response (LPR) and CD69 expression in response to stimulation with antigens, anti-CD3 monoclonal antibody, and mitogen. Dendritic cell maturation potential was assessed by phenotypic (CD80 and CD83 expression in stimulated monocyte-derived dendritic cells) and functional (the LPR of alloreactive T cells in mixed leukocyte reactions) analysis.

RESULTS

The potential of phenotypic and functional maturation of dendritic cells of subjects with SCI was significantly impaired compared with healthy controls, and that potential was worse for tetraplegic patients than for paraplegic patients. However, no significant difference was found in T-cell responses of CD4+ and CD8+ subsets between subjects with SCI and healthy controls.

CONCLUSIONS

Impaired maturation potential of dendritic cells is a novel defect in innate immunity in people with SCI.

Dendritic Cell Development in Long-Term Spleen Stromal Cultures

The cellular microenvironments in which dendritic cells (DCs) develop are not known. DCs are commonly expanded from CD34+ bone marrow precursors or blood monocytes using a cocktail of growth factors including GM-CSF. However, cytokine-supported cultures are not suitable for studying the intermediate stages of DC development, since progenitors are quickly driven to become mature DCs that undergo limited proliferation and survive for only a short period of time. This lab has developed a long-term culture (LTC) system from spleen which readily generates a high yield of DCs. Hematopoietic cells develop under more normal physiological conditions than in cultures supplemented with cytokines. A spleen stromal cell monolayer supports stem cell maintenance, renewal, and the specific differentiation of only DCs and no other hematopoietic cells. Cultures maintain continuous production of a small population of small-sized progenitors and a large population of fully developed DCs. Cell-cell interaction between stromal cells and progenitor cells is critical for DC differentiation. The progenitors maintained in LTC appear to be quite distinct from bone marrow-derived DC progenitors that respond to GM-CSF. The majority of cells produced in LTC are large-sized cells with a phenotype reflecting myeloid-like DC precursors or immature DCs. These cells are highly endocytotic and weakly immunostimulatory for T cells. This model system predicts in situ production of DCs in spleen from endogenous progenitors, as well as a central role for spleen in DC hematopoiesis.

Age Distribution for T Cell Reactivity to Vaccinia Virus in a Healthy Population

The potential for bioterrorism involving smallpox has led to a debate about the durability of protective immunity against smallpox from vaccination. By assessing the T cell reactivity to vaccinia virus in a healthy population, we show that subjects who were vaccinated within the past 3 decades and who have a visible vaccination scar had remarkable T cell reactivity. However, person who were vaccinated within the past 3 decades but who do not have a scar and those who were vaccinated >4 decades ago had responses as low as those in unvaccinated subjects. Thus, we estimate that the significant T cell memory response to vaccinia virus from successful vaccination may persist for only 20-30 years. Furthermore, we found the vaccinia-specific cellular immunity could be easily assessed by determination of the frequencies of vaccinia-specific CD69 expression on T cell subsets. These data may help in the development of public health strategies to counter bioterrorism threats associated with smallpox.

Induction of cytomegalovirus-specific CD4+ cytotoxic T lymphocytes from seropositive or negative healthy subjects or stem cell transplant recipients

OBJECTIVE

We generated cytomegalovirus (CMV)-specific cytotoxic T lymphocytes (CTL) in vitro using dendritic cells (DC) pulsed with crude CMV antigens (Ag).

PATIENTS AND METHODS

Mononuclear cells from healthy CMV-seropositive or seronegative volunteers and from stem cell transplant (SCT) recipients were cultured with CD14(+) monocyte-derived DC prepulsed with CMV Ag and then matured in vitro with lipopolysaccharide and tumor necrosis factor-alpha. After proliferation, cells were checked for phenotype (CD4/CD8), while killing activity was measured by 51Cr-release assay.

RESULTS

CD4(+) T cells, the main proliferating cells from both seropositive and seronegative individuals, killed autologous Ag-pulsed DC but not vehicle-pulsed autologous DC or CMV-pulsed allogeneic DC. Similar CTL induction was accomplished from SCT recipients. Significant killing of autologous CMV-infected fibroblasts required 16-hour incubation as opposed to the standard 4-hour incubation, which was prevented by either a perforin inhibitor or anti-Fas ligand monoclonal antibody. CTL enhanced surface HLA-DR expression of CMV-infected fibroblasts, and their activity was neutralized by anti-HLA-DR monoclonal antibody.

CONCLUSION

CMV-specific CD4(+) CTL were inducible with or without antiviral humoral immunity, even from immunosuppressed SCT recipients. These CTL showed perforin- and Fas/Fas ligand-mediated cytotoxicity after long-term (16-hour) contact with CMV-infected targets.

Differential impact of late-stage HIV-1 infection on in vitro and in vivo maturation of myeloid dendritic cells

The functional and phenotypic maturation of myeloid dendritic cells (DCs), circulating and monocyte-derived, from subjects at different stages of HIV-1 infection was evaluated. The results showed that the capacity of circulating DCs was significantly impaired in subjects with CD4+ T cell counts of <200/microL, correlated with the potential of CD40 ligand expression on CD4+ T cells (R = 0.84; P = 0.002), and improved with successful antiretroviral therapy. However, the function and phenotype of monocyte-derived DCs generated by in vitro culture from subjects at any stage of HIV-1 infection were similar to those in uninfected healthy subjects. Our findings suggest that although the potential of myeloid DC precursors to achieve full maturation is preserved in subjects with late-stage HIV-1 infection, in vivo maturation of myeloid DCs was impaired in these subjects, which may be due to decreased potential of CD40 ligand expression on CD4+ T cells. That myeloid DCs fail to achieve full maturation in vivo in late-stage HIV-1 infection may contribute to the failure to induce effective cellular immunity against HIV-1 and opportunistic pathogens.