Bianca A. N. Santos

CD4+ CD25+ Foxp3+ regulatory T cells, dendritic cells, and circulating cytokines in uncomplicated malaria: do different parasite species elicit similar host responses?

ABSTRACT Clearing blood-stage malaria parasites without inducing major host pathology requires a finely tuned balance between pro- and anti-inflammatory responses. The interplay between regulatory T (Treg) cells and dendritic cells (DCs) is one of the key determinants of this balance. Although experimental models have revealed various patterns of Treg cell expansion, DC maturation, and cytokine production according to the infecting malaria parasite species, no studies have compared all of these parameters in human infections with Plasmodium falciparum and P. vivax in the same setting of endemicity. Here we show that during uncomplicated acute malaria, both species induced a significant expansion of CD4+ CD25+ Foxp3+ Treg cells expressing the key immunomodulatory molecule CTLA-4 and a significant increase in the proportion of DCs that were plasmacytoid (CD123+), with a decrease in the myeloid/plasmacytoid DC ratio. These changes were proportional to parasite loads but correlated neither with the intensity of clinical symptoms nor with circulating cytokine levels. One-third of P. vivax-infected patients, but no P. falciparum-infected subjects, showed impaired maturation of circulating DCs, with low surface expression of CD86. Although vivax malaria patients overall had a less inflammatory cytokine response, with a higher interleukin-10 (IL-10)/tumor necrosis factor alpha (TNF-α) ratio, this finding did not translate to milder clinical manifestations than those of falciparum malaria patients. We discuss the potential implications of these findings for species-specific pathogenesis and long-lasting protective immunity to malaria.

IVIg Immune Reconstitution Treatment Alleviates the State of Persistent Immune Activation and Suppressed CD4 T Cell Counts in CVID

Common variable immunodeficiency (CVID) is characterized by defective B cell function, impaired antibody production, and increased susceptibility to bacterial infections. Here, we addressed the hypothesis that poor antibody-mediated immune control of infections may result in substantial perturbations in the T cell compartment. Newly diagnosed CVID patients were sampled before, and 6–12 months after, initiation of intravenous immunoglobulin (IVIg) therapy. Treatment-naïve CVID patients displayed suppressed CD4 T cell counts and myeloid dendritic cell (mDC) levels, as well as high levels of immune activation in CD8 T cells, CD4 T cells, and invariant natural killer T (iNKT) cells. Expression of co-stimulatory receptors CD80 and CD83 was elevated in mDCs and correlated with T cell activation. Levels of both FoxP3+ T regulatory (Treg) cells and iNKT cells were low, whereas soluble CD14 (sCD14), indicative of monocyte activation, was elevated. Importantly, immune reconstitution treatment with IVIg partially restored the CD4 T cell and mDC compartments. Treatment furthermore reduced the levels of CD8 T cell activation and mDC activation, whereas levels of Treg cells and iNKT cells remained low. Thus, primary deficiency in humoral immunity with impaired control of microbial infections is associated with significant pathological changes in cell-mediated immunity. Furthermore, therapeutic enhancement of humoral immunity with IVIg infusions alleviates several of these defects, indicating a relationship between poor antibody-mediated immune control of infections and the occurrence of abnormalities in the T cell and mDC compartments. These findings help our understanding of the immunopathogenesis of primary immunodeficiency, as well as acquired immunodeficiency caused by HIV-1 infection.

Dysregulated CD1 profile in myeloid dendritic cells in CVID is normalized by IVIg treatment.

To the editor: The CD1 proteins are major histocompatibility complex class I-like molecules specialized in presenting lipid and glycolipid antigens to T cells.[1][1] Group I CD1s include CD1a, CD1b, and CD1c and present bacterial antigens to a diverse repertoire of pathogen-specific T cells.[2][2]

CD4+ T-cell activation impairs serogroup C Neisseria meningitis vaccine response in HIV-infected children.

Objective:To investigate the influence of CD4+ T-cell activation and regulatory populations in HIV-infected children antibody response to vaccination with a conjugate C polysaccharide vaccine. Design:CD4+ T-cell activation was evaluated by expression of CD38, HLA-DR and CCR5 molecules. Regulatory CD4+ T cells (TReg) were characterized as FoxP3+CD127−CD25+ and inducer T cells (TInd) as CD4+FoxP3−CD25−CD39+. Methods:All patients (n = 36) were HIV-vertically infected, aged 2–17 years-old and were vaccinated with one vaccine injection. Blood samples were obtained before and after immunization to determine bactericidal antibody titers (SBA), CD4+ T-cell activation and frequency of TReg and TInd subsets (multiparametric flow cytometry). Results:Children not-responding (n = 18) to MenC vaccine expressed higher frequency of activated CD4+ T cells (HLA-DR+CD38+CCR5+) than responders (n = 18), both before and after vaccination (P < 0.05). A significant higher frequency of TReg was detected in responders compared with nonresponders (P = 0.0001). We also detected an inverse correlation between CD4+DR+CD38+CCR5+ (P = 0.01) or CD4+DR+CD38+ (P = 0.02) T cells and TReg cell frequency after vaccination. CD4+ T-cell activation negatively correlated (P = 0.006) with postvaccination SBA titers but a positive correlation (P = 0.0001) was detected between TReg cells and SBA. TReg and TInd subsets were inversely correlated (P = 0.04). Conclusion:Our findings suggest that higher CD4+ T-cell activation leads to poor vaccine response in children living with HIV, which may be associated with a TReg/TInd disequilibrium.

MAIT cells are activated in acute Dengue virus infection and after in vitro Zika virus infection

Dengue virus (DENV) and Zika virus (ZIKV) are members of the Flaviviridae and are predominantly transmitted via mosquito bites. Both viruses are responsible for a growing number of infections in tropical and subtropical regions. DENV infection can cause lethargy with severe morbidity and dengue shock syndrome leading to death in some cases. ZIKV is now linked with Guillain-Barré syndrome and fetal malformations including microcephaly and developmental disorders (congenital Zika syndrome). The protective and pathogenic roles played by the immune response in these infections is unknown. Mucosal-associated invariant T (MAIT) cells are a population of innate T cells with potent anti-bacterial activity. MAIT cells have also been postulated to play a role in the immune response to viral infections. In this study, we evaluated MAIT cell frequency, phenotype, and function in samples from subjects with acute and convalescent DENV infection. We found that in acute DENV infection, MAIT cells had elevated co-expression of the activation markers CD38 and HLA-DR and had a poor IFNγ response following bacterial stimulation. Furthermore, we found that MAIT cells can produce IFNγ in response to in vitro infection with ZIKV. This MAIT cell response was independent of MR1, but dependent on IL-12 and IL-18. Our results suggest that MAIT cells may play an important role in the immune response to Flavivirus infections.

Loss of Circulating Mucosal-Associated Invariant T Cells in Common Variable Immunodeficiency Is Associated with Immune Activation and Loss of Eomes and PLZF

Common variable immunodeficiency (CVID) is characterized by low levels of Igs leading to increased risk of infections. Mucosal-associated invariant T (MAIT) cells are a recently identified population of innate T cells with potent antibacterial activity. We hypothesized that CVID is associated with alterations in MAIT cells. Cryopreserved PBMC from CVID patients and healthy controls were used to study the frequency, phenotype, and response to Escherichia coli stimulation of MAIT cells by flow cytometry. MAIT cell frequency and absolute counts were depressed in CVID. Residual MAIT presented elevated coexpression of CD38 and HLA-DR, and reduced expression of CCR6, whereas levels of CD127 (IL-7 receptor) were unchanged. CVID patients also had an accumulation of MAIT cells lacking the critical transcription factors eomesodermin and promyelocytic leukemia zinc finger protein. MAIT cell frequency was inversely associated with levels of soluble CD14, with coexpression of CD38 and HLA-DR, and accumulation of MAIT cells lacking eomesodermin or promyelocytic leukemia zinc finger protein expression. None of these changes were normalized by IgG replacement therapy. Finally, MAIT cells from CVID patients displayed poor IFN-γ responses to E. coli stimulation, in part due to defective Ag presentation, and these responses were increased by pretreatment with IL-7. Defective MAIT cell response may contribute to the increased incidence of microbial infections seen in CVID patients on IgG replacement therapy.

Thymopoiesis and regulatory T cells in healthy children and adolescents

OBJECTIVES: The purpose of this study was to investigate the association between T cell receptor excision circle levels in peripheral blood mononuclear cells and regulatory T cells that co-express CD25 and Foxp3 in healthy children and adolescents of different ages. MATERIALS AND METHODS: The quantification of signal-joint T-cell receptor excision circle levels in the genomic DNA of peripheral blood mononuclear cells was performed using real-time quantitative PCR. The analysis of CD4, CD8, CD25, and Foxp3 expression was performed using flow cytometry. RESULTS: Ninety-five healthy controls (46 females and 49 males) ranging in age from 1 to 18 years were analyzed. The mean T-cell receptor excision circle count in all individuals was 89.095±36.790 T-cell receptor excision circles per microgram of DNA. There was an inverse correlation between T-cell receptor excision circles counts and age (r = -0.846; p<0.001) as well as between the proportion of CD4+CD25+Foxp3+ T cells and age (r = -0.467; p = 0.04). In addition, we observed a positive correlation between the amount of CD4+CD25+Foxp3+ T cells and the amount of T-cell receptor excision circles per microgram of DNA in individuals of all ages (r = -0.529; p = 0.02). CONCLUSIONS: In this study, we observed a decrease in the thymic function with age based on the fact that the level of T-cell receptor excision circles in the peripheral blood positively correlated with the proportion of regulatory T cells in healthy children and adolescents. These findings indicate that although T-cell receptor excision circles and regulatory T cells levels decrease with age, homeostasis of the immune system and relative regulatory T cells population levels are maintained in the peripheral blood.

Inversion of the Vδ1 to Vδ2 γδ T cell ratio in CVID is not restored by IVIg and is associated with immune activation and exhaustion.

AbstractCommon variable immunodeficiency (CVID) is defined by low levels of IgG and IgA, but perturbations in T cells are also commonly found. However, there is limited information on &ggr;&dgr; T cells in CVID patients. Newly diagnosed CVID patients (n = 15) were enrolled before and after intravenous IgG (IVIg) replacement therapy. Cryopreserved peripheral blood mononuclear cells were then used to study &ggr;&dgr; T cells and CVID patients were compared to healthy controls (n = 22). The frequency and absolute count of V&dgr;1 &ggr;&dgr; T cells was found to be increased in CVID (median 0.60% vs 2.64%, P <0.01 and 7.5 vs 39, P <0.01 respectively), while they were decreased for V&dgr;2 &ggr;&dgr; T cells (median, 2.36% vs 0.74%, P <0.01 and 37.8 vs 13.9, P <0.01 respectively) resulting in an inversion of the V&dgr;1 to V&dgr;2 ratio (0.24 vs 1.4, P <0.001). Markers of immune activation were elevated on all subsets of &ggr;&dgr; T cells, and HLA-DR expression was associated with an expansion of V&dgr;1 &ggr;&dgr; T cells (r = 0.73, P = 0.003). Elevated PD-1 expression was found only on V&dgr;2 &ggr;&dgr; T cells (median 1.15% vs 3.08%, P <0.001) and was associated with the decrease of V&dgr;2 &ggr;&dgr; T cells (r = −0.67, P = 0.007). IVIg had no effect on the frequency of V&dgr;1 and V&dgr;2 &ggr;&dgr; T cells or HLA-DR expression, but alleviated CD38 expression on V&dgr;1 &ggr;&dgr; T cells (median MFI 965 vs 736, P <0.05). These findings suggest that immunological perturbations of &ggr;&dgr; T cells are a general feature associated with CVID and are only partially reversed by IVIg therapy.