Biomedical subjects

Iulia Popescu

Publications and source records attributed to Iulia Popescu.

5 recordsLinked to original sources

PubMed2006

Detection of CD8+ T cells sensitized to BK virus large T antigen in healthy volunteers and kidney transplant recipients.

BK virus (BKV) infections after renal transplantation are increasingly recognized. Development of immune monitoring strategies against BKV requires definition of antigenic epitopes. Hence, T cells from HLA-A02-positive healthy subjects and kidney transplant recipients were stimulated by BKV lysate pulsed on mature autologous dendritic cells and screened against four different T antigen peptides or against BKV lysate. IFN-gamma production was measured by ELISPOT assays. The peptide BKV362-371 (MLTERFNHIL) was naturally processed and recognized by five of six healthy subjects (39 +/- 11 IFN-gamma spots/100,000 cells) and five of seven kidney transplant recipients (21 +/- 12 IFN-gamma spots). Less frequent and weaker CD8+ T-cell responses were detected against three other peptides. Thus, BKV large T antigen is a target for CD8+ T-cell immunity. T-antigen-specific T-cytotoxic cells circulate in healthy blood donors, implying that transient expression of T antigen presumably occurs at sites of viral latency and helps maintain a constant pool of circulating CD8+ T memory cells.

Adult↗

PubMed2005

EBV-specific memory CD8+ T cell phenotype and function in stable solid organ transplant patients.

Immune responses to EBV in immunosuppressed (IS) solid organ transplant (SOTx) recipients have not been well characterized. Here we evaluate the phenotype and function of EBV-specific CD8+ T cells in peripheral blood isolated from "stable" IS SOTx recipients. The EBV-specific CD8+ T cell memory subset distribution in the peripheral blood of patients was examined by flow cytometric analysis using HLA-A2 tetramers incorporating BMLF1 (lytic), and LMP2 and EBNA3A (latent)-derived peptides, in conjunction with mAbs against the CD45RO, CD45RA, and CD62L markers. The ability of CD8+ T cells to produce IFN-gamma in response to the same EBV-derived peptides was measured by ELISPOT assay. Patients and healthy normal donors exhibited similar anti-EBV CD8+ T cell frequencies and specificities against the EBV epitopes evaluated. When compared to healthy normal donors, an overall significant expansion of the CD8+ T cell "effector memory" (CD45RO+/CD62L-) pool, including that of EBV "latent" (LMP2 and EBNA3A)-specific CD8+ T cells was detected in IS SOTx patients. However, the patients' EBV-specific CD8+ T cells showed decreased IFN-gamma production to the EBV-peptide stimulation. These results indicate that the impairment of EBV-specific CD8+ T cell activity is not due to clonal depletion, but is mainly due to impaired functional activation.

Antigens, Viral↗

PubMed2005

Augmentation of type-1 polarizing ability of monocyte-derived dendritic cells from chronically immunosuppressed organ-transplant recipients.

BACKGROUND: Chronic immunosuppressive (IS) therapy impairs normal T-cell immune surveillance and may predispose to opportunistic infections and malignancies that represent life-threatening complication of solid-organ transplantation (SOTx). Our study was designed to ascertain the impact of chronic in vivo administration of IS on the ability of monocyte-derived dendritic cells (MoDC) to differentiate, mature, and function ex vivo. The potential of these cells to be implemented for DC-based adoptive immunotherapy was also considered. METHODS: MoDCs were propagated by conventional procedures, their phenotype was analyzed by flow cytometry, and their function was assessed by mixed leukocyte reaction, enzyme-linked immunoadsorbent assay, and ELISPOT assays. Nuclear translocation of nuclear factor (NF)-kB was analyzed by electrophoretic mobility shift assay. RESULTS: Circulating DC1s in peripheral blood were reduced in SOTx patients. MoDCs generated from patients displayed higher endocytic activity versus normal DCs, indicating their comparative immaturity. Patients' DCs exposed to pro-inflammatory cytokines (tumor necrosis factor-alpha, interleukin [IL]-1beta, and IL-6) were less able to mature, to stimulate recall antigen (Ag)- or allo-Ag-induced proliferation responses, or to secrete IL-12p70. These deficiencies were associated with a decrease in NF-kB translocation. In contrast, combination of pro-inflammatory cytokines and interferon (IFN)-gamma (a Th1-polarizing factor) augmented patients' DC1-type function and IL-12p70 production by way of an NF-kB-independent mechanism. CONCLUSIONS: Chronic IS restrains DC differentiation, maturation, and function at a transcriptional level; however, type-1 polarizing potential of patients' DC1 can be augmented ex vivo by a two-signal stimulation provided by pro-inflammatory cytokines and IFN-gamma. These results may have implications for DC-based immunotherapy of malignancies in the transplantation setting.

Active Transport, Cell Nucleus↗

PubMed2003

Human NK cells express Fc receptors for IgA which mediate signal transduction and target cell killing.

Receptors for the Fc region of IgG (FcgammaRIIIa, FcgammaRIIc) and IgM (FcmicroR) were previously described on NK cells. In this work the expression of Fc receptors for IgA (FcalphaR) on human NK cells and the signaling events were investigated. The FcalphaR was demonstrated by flow cytometry using secretory IgA (sIgA) and anti-human IgA antibody. The percentage of NK cells (CD3(-)CD56(+)CD16(+)) expressing FcalphaR ranged between 55.7% and 95.7%, with a mean +/- SD of 75.2+/-11.8. The association constant and the number of (125)I-labeled sIgA ((125)I-sIgA) molecules bound per cell, calculated by Scatchard analysis, were 2 x 10(7) M(-1) and 1.7 x 10(4), respectively. The binding specificity was proved by inhibition experiments. Cold sIgA but not IgA Fab fragments were able to inhibit (125)I-sIgA binding in a concentration-dependent manner. Binding of sIgA to NK cells was neither inhibited by anti-mannose receptor antibody, nor by L-fucose, D-galactose, D-glucose, D-mannose or N-acetyl-D-glucosamine. Pretreatment of NK cells with polymeric IgA inhibited their capacity to kill (51)Cr-labeled K562 target cells by 34.8%, whereas with monomeric IgA only by 13.1%. Ligand-induced clustering of the FcalphaR resulted in activation of tyrosine kinases Lck, Syk and phosphatidylinositol 3-kinase. The present studies support the concept that human NK cells bind preferentially sIgA and polymeric IgA with moderate affinity via FcalphaR, which is different from the FcalphaRI/CD89 and other carbohydrate-recognizing receptors like mannose receptor/CD206. This novel structure mediates signal transduction and cell killing.

Binding Sites↗

PubMed2003

Ex vivo priming of naïve T cells into EBV-specific Th1/Tc1 effector cells by mature autologous DC loaded with apoptotic/necrotic LCL.

Posttransplant lymphoproliferative disorders (PTLDs) represent life-threatening complications of bone marrow and solid organ transplantation (SOTx). These are B-cell malignancies triggered by Epstein-Barr Virus (EBV) infection in chronically immunosuppressed (IS) recipients. Immunosuppressed EBV seronegative (EBV(-)) organ recipients are at highest risk of developing PTLD owing to the lack of anti-EBV memory T cells to control subsequent EBV challenges. Our aim is to establish effective anti-EBV T-cell generation protocols for prevention or treatment of PTLD encountered in SOTx. We have used autologous dendritic cells (DCs) loaded with apoptotic/necrotic lymphoblastoid cell lines (LCLs) to evaluate the ability of such an approach to activate naïve T cells in vitro. In EBV(-) individuals, both CD8+ and CD4+ T-cell responses were amplified by this approach, as detected by IFN-gamma ELISPOT and cytotoxicity assays. The CD8+ T cells were poly-specific anti-EBNA3 A, -LMP2 and -BMLF1, with uniform reversion to a CD45RO+/RA-phenotype, decreased CD62L expression, and up-regulation of the activation markers CD28 and CD69. Addition of rhIL-12 improved anti-viral T-cell responses and reduced the functional differences observed between EBV(+) and EBV(-) responders. In conclusion, the DC/LCL method promotes cross-presentation of EBV-associated epitopes and may serve as an effective protocol for the adoptive immunotherapy of PTLD in EBV(-) SOTx patients.

Antigen Presentation↗