Yvonne Rosenstein

Oestradiol potentiates the suppressive function of human CD4 + CD25 + regulatory T cells by promoting their proliferation

CD4+ CD25+ regulatory T (Treg) cells play an important role in the control of the immune system by suppressing the proliferation of effector cells, thereby preventing autoreactive, unnecessary or inconvenient responses. Recently, it has been shown that the number of Treg cells increases during pregnancy, a period with high serum levels of female sex hormones. Oestrogen replacement therapy has been reported to alleviate the symptoms of autoimmune diseases, yet the cellular and molecular mechanisms involved are not fully understood. Here, we show that physiological doses of oestradiol (E2) found during pregnancy, combined with activation through CD3/CD28 engagement, promoted the proliferation of Treg cells without altering their suppressive phenotype. Enhanced suppression was detected when Treg cells were pretreated with the hormone as well as when both cell subpopulations (Treg and T effector) were exposed to E2 throughout the experiment. Together, these data suggest that when combined with an activating stimulus, E2 can modulate the function of human Treg cells by regulating their numbers, and highlight a potential use of E2, or its analogs, to manipulate Treg function.

Multifunctional host defense peptides: Antimicrobial peptides, the small yet big players in innate and adaptive immunity

The term ‘antimicrobial peptides’ refers to a large number of peptides first characterized on the basis of their antibiotic and antifungal activities. In addition to their role as endogenous antibiotics, antimicrobial peptides, also called host defense peptides, participate in multiple aspects of immunity (inflammation, wound repair, and regulation of the adaptive immune system) as well as in maintaining homeostasis. The possibility of utilizing these multifunctional molecules to effectively combat the ever‐growing group of antibiotic‐resistant pathogens has intensified research aimed at improving their antibiotic activity and therapeutic potential, without the burden of an exacerbated inflammatory response, but conserving their immunomodulatory potential. In this minireview, we focus on the contribution of small cationic antimicrobial peptides – particularly human cathelicidins and defensins – to the immune response and disease, highlighting recent advances in our understanding of the roles of these multifunctional molecules.

Inhibitory effect of Fusarium T2-toxin on lymphoid DNA and protein synthesis.

The effect of T2-toxin on DNA and protein synthesis was investigated, both in vivo and in vitro. For mice which had been submitted to different treatment schedules (single dose, 3-, or 7-day treatment), the rate of DNA and protein biosynthesis was measured in thymus, bone marrow, liver, and spleen cells. T2-toxin inhibited DNA and protein synthesis, irrespectively of treatment schedule, in bone marrow, spleen, and thymus. In liver, after 3-day treatment, DNA and protein synthesis were both enhanced as compared to control values, whereas after 7-day treatment, only protein synthesis values remained greater than those of controls, and DNA synthesis was inhibited. After 7-day treatment, ornithine decarboxylase activity was inhibited in the thymus. In vitro, T2-toxin inhibited DNA and protein synthesis of mice spleen cells stimulated with phytohemagglutinin and rat hepatoma cells.

What it takes to become an effector T cell: The process, the cells involved, and the mechanisms

When activated, CD4+ T cells differentiate into two major sub‐populations differing in their profiles of secreted cytokines. Type One, or TH1, cells secrete IL‐2, IFNγ, and TNFβ and mediate a cellular immune response. Type Two, or TH2, cells secrete IL‐4, IL‐5, IL‐6, IL‐10, and IL‐13 and potentiate a humoral response. The nature of any specific immune response depends on the interaction of antigen‐presenting cells and T cells. The role of antigen‐presenting cells is to respond to the nature of the immune challenge and signal differentiation of CD4+ T cells. A number of factors are involved in the effector phenotype of T cells—nature and affinity of antigen, co‐receptors signals, and cytokine environment. T‐cell differentiation is a complex process comprising four defined developmental stages: activation of particular cytokine genes, commitment of the cells, silencing of the opposing cytokine genes, and stabilization of the phenotype. In each of these stages, the cells respond to the products of many signaling cascades from many membrane‐bound receptors. The stages in development are mediated by different molecular mechanisms, involving control of gene expression and chromatin remodeling. This review centers on the factors, cellular interactions, and molecular mechanisms involved in the maturation of naïve CD4+ T lymphocytes into fully effector cells.

Expression of CD64 as a potential marker of neonatal sepsis

The aim of this study was to identify a novel immunological indicator useful for the early diagnosis (through a rapid and single determination) of neonatal sepsis (NS). Peripheral blood samples were taken from 63 neonates, who were classified into four groups: proven NS (n = 17); clinical NS (n = 14); disease without infection (n = 17); and healthy newborns (n = 15). Neutrophil expression of CD64, CD43, CD44, CD50, CD62L and Mac‐1, and plasma levels of interleukin (IL)‐1β, IL‐6, tumor necrosis factor‐α (TNF‐α) and soluble L‐selectin (sCD62L), were determined. Expression of CD64 was significantly enhanced in the group with proven sepsis and clinical NS compared to newborns without infection (p < 0.05). Eight newborns with proven or clinical sepsis, but only one with disease without infection, showed an increased percentage of CD64+ cells (diagnostic specificity = 96.8%). No significant differences were found in the expression of the other leucocyte differentiation antigens studied. As previously described, TNF‐α and IL‐6 levels were significantly elevated in newborns with proven or clinical sepsis compared to neonates without infection (p < 0.05). Our results suggest that, through a single determination, the enhanced expression of CD64 is a highly specific indicator of NS, although its diagnostic sensitivity is low (25.8%). In contrast, we found that plasma levels of IL‐1β and sCD62L, as well as the expression of Mac‐1, CD43, CD44, CD50, and CD62L, do not appear to be useful for the diagnosis of NS.

CD43-specific Activation of T Cells Induces Association of CD43 to Fyn Kinase

CD43, the most abundant membrane protein of T lymphocytes, is able to initiate signal transduction pathways that lead to Ca2+ mobilization and interleukin-2 production, yet the molecular events involved in CD43s signal transduction pathway are poorly understood. In the present report we show that activation of both purified T lymphocytes and Jurkat cells, through CD43 cross-linking with the anti-CD43 L10 monoclonal antibody, induced CD43 association to Fyn kinase. This association is mediated by the Src homology 3 (SH3) domain of Fyn, since a glutathione S-transferase-Fyn SH3 fusion protein was able to precipitate CD43 from lysates of CD43-activated T cells. A synthetic peptide containing the SH3 binding sites of p85, located within the amino acid sequence 300ERQPAPALPPKPPKP314, was able to inhibit binding of CD43 to Fyn as well as to the glutathione S-transferase-Fyn SH3 fusion protein. We also provide evidence that upon CD43 cross-linking, Fyn is tyrosine-phosphorylated in a time-dependent manner. Our results suggest that CD43 cross-linking on the T cell surface induces the interaction between CD43 and Fyn, presumably through the Fyn SH3 domain and a putative SH3 binding site in CD43, leading to Fyn tyrosine phosphorylation and signal propagation.

Immunosuppressive effects of Fusarium extracts and trichothecenes: blastogenic response of murine splenic and thymic cells to mitogens.

Summary The effects of Fusarium extract and its principal components (T2-toxin, di-acetoxyscirpenol and Butenolide) on the immune system were tested in mice. Animals were treated with these mycotox-ins, and the mitogen responsiveness of spleen or thymic cells was examined. The stimulation of both T and B cells was found to be reversibly inhibited. Also, the ability to synthesize anti-SRBC antibodies was reversibly suppressed. The direct effect of mycotoxins was tested in vitro in lymphocyte and fibrosarcoma cell cultures. These compounds exerted a direct cytostatic effect at high concentrations, and a stimulating effect at low concentration. Profound histological changes were observed in thymus and spleen after treatment, while under the experimental conditions employed, the histology of other organ systems was not affected.

CD43, a molecule with multiple functions.

To initiate a specific immune response, lymphoid cells integrate a variety of signals generated through the orchestrated interaction of multiple cell surface molecules with their counter-receptors. As a result of the specific recognition of the antigen through antigenspecific receptors, and of the monitoring of their particular environment through the so-called coreceptor molecules, lymphoid cells go through elaborate processes of maturation and activation, contributing to the plasticity and sensitivity of immune response. CD43 is the major sialic acid rich protein on the surface of lymphocytes. However, the specific roles of this protein in different lymphoid cells under normal physiological conditions remain largely unknown. In this review we will mainly focus on the recent advances concerning the functions of this molecule as a coreceptor of different lymphoid cells as well as on the participation of this molecule in different pathologies.

The innate immune response to Entamoeba histolytica lipopeptidophosphoglycan is mediated by toll-like receptors 2 and 4

Entamoeba histolytica is a human pathogen that may invade the intestinal mucosa, causing amoebic colitis or hepatic abscesses when the trophozoites travel through the portal circulation to the liver. Lipopeptidophosphoglycan (LPPG) is a molecular pattern of E. histolytica recognized by the human immune system. Here we report that LPPG is exposed on the cell surface of E. histolytica trophozoites, and is recognized by the host through toll‐like receptor (TLR) 2 and TLR4. Correspondingly, human embryonic kidney (HEK)‐293 cells were rendered LPPG responsive through overexpression of TLR2 or TLR4/MD2. Moreover, co‐expression of CD14 enhanced LPPG signal transmission through TLR2 and TLR4. The interaction of LPPG with TLR2 and TLR4 resulted in activation of NF‐κB and release of interleukin (IL)‐10, IL‐12p40, tumour necrosis factor (TNF)‐α, and IL‐8 from human monocytes. Consistent with these findings, responsiveness of mouse macrophages lacking TLR2 expression (TLR2–/–) or functional TLR4 (TLR4d/d) to E. histolytica LPPG challenge was impaired while double deficient macrophages were unresponsive. In contrast to wild‐type control and TLR2–/–animals succumbing to lethal shock syndrome, TLR4d/dmice were resistant to systemic LPPG challenge‐induced pathology.

CD8 Cells of Patients with Diffuse Cutaneous Leishmaniasis Display Functional Exhaustion: The Latter Is Reversed, In Vitro, by TLR2 Agonists

Leishmania mexicana (Lm) causes localized (LCL) and diffuse (DCL) cutaneous leishmaniasis. DCL patients have a poor cellular immune response leading to chronicity. It has been proposed that CD8 T lymphocytes (CD8) play a crucial role in infection clearance, although the role of CD8 cytotoxicity in disease control has not been elucidated. Lesions of DCL patients have been shown to harbor low numbers of CD8, as compared to patients with LCL, and leishmanicidal treatment restores CD8 numbers. The marked response of CD8 towards Leishmania parasites led us to analyze possible functional differences between CD8 from patients with LCL and DCL. We compared IFNγ production, antigen-specific proliferation, and cytotoxicity of CD8 purified from PBMC against autologous macrophages (MO) infected with Leishmania mexicana (MOi). Additionally, we analyzed tissue biopsies from both groups of patients for evidence of cytotoxicity associated with apoptotic cells in the lesions. We found that CD8 cell of DCL patients exhibited low cytotoxicity, low antigen-specific proliferation and low IFNγ production when stimulated with MOi, as compared to LCL patients. Additionally, DCL patients had significantly less TUNEL+ cells in their lesions. These characteristics are similar to cellular “exhaustion” described in chronic infections. We intended to restore the functional capacity of CD8 cells of DCL patients by preincubating them with TLR2 agonists: Lm lipophosphoglycan (LPG) or Pam3Cys. Cytotoxicity against MOi, antigen-specific proliferation and IFNγ production were restored with both stimuli, whereas PD-1 (a molecule associated with cellular exhaustion) expression, was reduced. Our work suggests that CD8 response is associated with control of Lm infection in LCL patients and that chronic infection in DCL patients leads to a state of CD8 functional exhaustion, which could facilitate disease spread. This is the first report that shows the presence of functionally exhausted CD8 T lymphocytes in DCL patients and, additionally, that pre-stimulation with TLR2 ligands can restore the effector mechanisms of CD8 T lymphocytes from DCL patients against Leishmania mexicana-infected macrophages.