1,720,983 research outputs found
HCV and lymphoproliferative disorders
No full textThe etiology of non-Hodgkin's lymphomas (NHL) remains a controversial matter, but, in the last few years, considerable evidence suggests that aberrations of the immune system and viruses may act as etiologic agents, in at least some cases of NHL. In fact, patients with primary immuno-deficiencies, or those suffering from diseases characterized by autoimmune dysfunction, show an increased risk for the development of NHL. Several viruses have been identified as possible etiologic agents for NHL; one of the best studied is the Epstein-Barr virus, which was detected in cultures of tumor cells from patients with Burkitt's lymphoma. The pathogenetic potential of this virus is illustrated by its association with an increasing number of malignant diseases. In addition, the human T-cell lymphotropic virus family (HTLV), was also recognized as possible etiologic agents for several lymphomas, such as cutaneous T-cell lymphoma and T-cell leukemia-lymphoma syndrome (HTLV-I), and T-cell hairy cell leukemia (HTLV-II). Recently, the presence of hepatitis C virus infection has also been recognized in several hematological malignancies such as mixed cryoglobulinemia, low-grade malignant lymphomas and Waldenström's disease. The possible etiopathogenetic role of this virus in non-Hodgkin's lymphomas is discussed on the basis of molecular, clinical, and epidemiological considerations
Efficient folding of the FcεRI α-chain membrane-proximal domain D2 depends on the presence of the N-terminal domain D1
No full textHuman high affinity receptor for IgE is a membrane glycoprotein multi-chain complex presenting two extracellular Ig modules in its α-chain (D1D2). The receptor IgE binding region is located within the membrane-proximal module D2, while the N-terminal module D1 appears to promote an optimal receptor conformation for IgE binding. To understand the structural relationship between the two modules, we dissected FcεRI α-chain into its discrete Ig units and expressed them in mammalian cells. Unexpectedly, D2 was secreted as a disulphide-linked dimer, while D1 was monomeric. Active secretion and full glycosylation of dimeric D2 suggest a native-like conformation of the protein, justifying the escape from the endoplasmic reticulum/Golgi quality control systems. We then propose a domain-swapping model for D2, in which two interdigitated polypeptide chains assume the overall conformation of two Ig modules, as observed for rat CD2 N-terminal domain. Fusion of an unrelated Ig fold moiety at the N terminus of D2 did not interfere with its dimerisation. While D1D2 assumes a correct fold, co-expression of both isolated domains in the same cell did not restore monomeric folding of D2. Thus, D1 appears to assist the appropriate folding of FcεRI α-chain, acting as an uncleavable intramolecular chaperone-like block towards D2. © 2002 Elsevier Science Ltd. All rights reserved
CD57+ T lymphocytes and functional immune deficiency
No full textAbstract
CD57(+) expression in T lymphocytes has been recognized for decades as a marker of in vitro replicative senescence. In recent years, accumulating evidences have pointed on the utility of this marker to measure functional immune deficiency in patients with autoimmune disease, infectious diseases, and cancers. We review here the relevant literature and implications in clinical settings
A minimal receptor-Ig chimera of human FcεRI α-chain efficiently binds secretory and membrane IgE
No full textWe constructed a soluble minimal receptor-Ig chimera in which the two extracellular domains of human FcεRI α-chain (D1 and D2) were fused to the dimerizing C-terminal domain of human IgG1 heavy chain (γ1-CH3). The protein was expressed and actively secreted by Chinese hamster ovary (CHO) cells as a fully glycosylated soluble dimeric protein. It showed efficient binding both to human membrane-bound IgE isoforms and to the two secretory IgE isoforms. Moreover, the dimeric receptor binds IgE with the expected 1:2 stoichiometry. The receptor-Ig chimera, in 2-fold molar excess, inhibited engagement of secretory IgE to rat basophilic leukemia cells expressing the human αβγ receptor. Full self-nature and inability to bind Fcγ receptors make this protein an attractive candidate for clinical applications and a novel biotechnological tool for atopic allergy research
Rotavirus Replication Requires a Functional Proteasome for Effective Assembly of Viroplasms
No full textThe ubiquitin-proteasome system has been shown to play an important role in the replication cycle of different viruses. In this study, we describe a strong impairment of rotavirus replication upon inhibition of proteasomal activity. The effect was evidenced at the level of accumulation of viral proteins, viral RNA, and yield of infective particles. Kinetic studies revealed that the early steps of the replicative cycle following attachment, entry, and uncoating were clearly more sensitive to proteasome inhibition. We ruled out a direct inhibition of the viral polymerase activities and stability of viral proteins and found that the crucial step that was impaired by blocking proteasome activity was the assembly of new viroplasms. This was demonstrated by using chemical inhibitors of proteasome and by gene silencing using small interfering RNAs (siRNAs) specific for different proteasomal subunits and for the ubiquitin precursor RPS27A. In addition, we show that the effect of proteasome inhibition on virus infection is not due to increased levels of beta interferon (IFN-β)
The leukemic cell of chronic lymphocytic leukemia patients with autoimmune hemolitic anemia produce isotype-switched immunoglobulins that are preferentially encoded by the 51p1 and DP-50 VH genes
No full textThe observed skewing in the repertoire of VH, D, and JH gene segments strongly indicates that the leukemic Igs in CLL patients with AIHA have been selected because of particular antigen specificities that could promote the development of the hemolytic anemia. This could occur either by a direct involvement of the CLL Ig in erythrocyte destruction or, indirectly, by inducing the production of pathogenic antierythrocyte antibodies. The first possibility was supported by our recent finding that in most CLL cases a small subset of leukemic cells undergoes Ig isotype-switching.9 The isotypeswitched CLL cells were found to produce both membrane and secretory -chain transcripts, of which the latter could encode part of the IgG antibodies that have been implicated in RBC destruction. To test this hypothesis, we investigated the reactivity of the Igs expressed by the leukemic cells from the CLL-AIHA patients HA-2 and HA-5. These two Igs contained strikingly similar heavy-chain CDR3 regions that were associated with the 51p1 VH gene segment; both of them used λ light chains that belonged to different Vλ gene families (HA-2VL is 95.5% homologous to Humlv 122 from the VλI family, and HA-5VL is 93% homologous to Humlv318 from the VλIII family). The VH and VL region genes from these two Igs were expressed in eukaryotic cell lines as dimeric single-chain (sc) Fv fragments, and their reactivities were tested against erythrocytes and a panel of self and foreign antigens. Indirect immunofluorescence analysis with the affinity-purified scFv fragments showed the absence of any significant RBC binding. On the other hand, both antibody fragments showed similar low-affinity binding to human IgG (FIGURE 1B) and various reactivities against other antigens such as phosphorylcholine, dextran, lipopolysaccharide, and single-stranded DNA. These data indicate that the 51pl-encoded CLL Igs are not directly involved in RBC destruction, but could promote the development of AIHA by inducing a disturbance in the idiotypic network that would ultimately lead to the expansion of autoreactive B cell clones with antierythrocyte specificity. Alternatively, secreted isotype-switched CLL Igs could bind to anti-RBC antibodies and could promote the adherence of sensitized red blood cells to the Fc receptors on macrophages
HCV-associated autoimmune haemolityc anaemia due to warm-reacting antibodies: evidence of B-cell monoconality
No full textBinders based on dimerised immunoglobulin VH domains
No full textAntibody binding to antigen is mediated by the surface formed by the association of the two variable (V) regions of the L (VL) and H (VH) chains. The capacity of VL to dimerise and the high structural similarity of VL and VH domains suggested the possibility that VH could also associate. We show here that spontaneous formation of VH dimers (VHD) is in many cases permissive, producing stable molecules with antigen binding specificity. VHD were displayed on filamentous phages for the selection of antigen-specific binders. VHD were expressed and secreted efficiently from both bacteria and mammalian cells in different formats, including single-chain (VH(1)-linker-VH(2)), double chain ((VH(2)) and IgG analogues having the VL replaced by VH. The affinity (Kd,app) achieved with a VH dimer expressed in the IgG format, specific for a glutenin subunit was around 30 nM measured by two different methods, which was about 20 times higher than that corresponding to the VL/VH counterpart
Membrane immunoglobulins are stabilized by interchain disulfide bonds occurring within the extracellular membrane-proximal domain
No full textMembrane-bound immunoglobulins have, in addition to the transmembrane and cytoplasmic portions, an extracellular membrane-proximal domain (EMPD), absent in the secretory forms. EMPDs of immunoglobulin isotypes α, γ, and ε contain cysteines whose role has so far not been elucidated. Using a genetic strategy, we investigated the ability of these cysteines to form disulfide bridges. Shortened versions of human membrane immunoglobulins, depleted of cysteines known to form intermolecular disulfide bonds, were constructed and expressed on the surface of a B-cell line. The resulting membrane proteins contain a single chain fragment of variable regions (scFv) linked to the dimerizing domain from the immunoglobulin heavy chains (CH3 for α and γ or CH4 for ε isotypes), followed by the corresponding EMPD and the transmembrane and cytoplasmic domains. The two functional membrane versions of the ε chain, containing the short and long EMPD, were analyzed. Our results show that the single cysteine within α1L and γ1 EMPD and the short version of ε EMPD form an interchain disulfide bond. Conversely, the cysteine resident in the ε transmembrane domain remains unreacted. ε-long EMPD contains four cysteines; two are involved in interchain bonds while the remaining two are likely forming an intrachain bridge. Expression of a full-length membrane ε heavy chain mutant, in which Cys121 and Cys209 within domain CH2 (involved in interchain bridges) were mutated to alanines, confirmed that, within the complete IgE, EMPD cysteines form interchain disulfide bonds. In conclusion, we unveil evidence for additional covalent stabilization of membrane-bound immunoglobulins
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