The regulation mechanism of HLA class II gene expression at the level of mRNA stability

The number of major histocompatibility complex (MHC) class II antigens may be regulated at different levels. Although transcriptional regulation has been studied most intensely, evidence for control mechanisms acting on the stability of MHC class II mRNAs has been reported. We have previously shown, in fact, that the half-life of MHC class II mRNA rapidly decreases in Raji cells upon inhibition of translation by cycloheximide; further data indicated that this effect was not correlated with the inhibition of the synthesis of trans-acting protein(s) required for mRNA stability. In the present work, we developed an in vitro mRNA decay assay system to measure HLA-DRA mRNA stability and used inhibitors of protein synthesis affecting different steps of the process of translation in order to discriminate among possible mechanisms determining controlled MHC class II mRNA hydrolysis. We found that HLA-DRA mRNA associated with polysomes derived from cells treated with either puromycin (which causes dispersion of polysomes and accumulation of monosomes) or cycloheximide (which slows down translation causing ribosome stalling) is more rapidly degraded than in the absence of protein synthesis inhibitors. On the basis of our findings, we suggest that arrest of protein synthesis per se exposes the HLA-DRA mRNA molecules to degradative activities co-sedimenting with the polysomal fraction.

Antigenicity of HIV-derived T helper determinants in the context of carrier recombinant proteins: effect on T helper cell repertoire selection

T helper (Th) epitopes can be included in a recombinant protein with B and CTL epitopes to create more effective immunogens. To determine whether the antigenicity of HIV Th epitopes is preserved in this altered molecular context, human Th clones specific for peptides of HIV gp120 and reverse transcriptase p66 were challenged with recombinant proteins carrying the antigenic epitopes in different sites. We found that a given epitope was recognized by a specific T cell clone only when it was inserted in a particular position of the carrier. However, the permissive position was not the same for all epitopes. Enzymatic excision from a nonpermissive context or insertion of a polyserine spacer between the epitope and the carrier restored antigenicity. Nevertheless, antigenicity was not abolished in a synthetic peptide encompassing the epitope and the neighboring residues from the nonpermissive location. These data suggest that, in this case, the primary sequence of the chimeric protein flanking the HIV peptide is not responsible for loss of antigenicity. Furthermore, constructs carrying the epitope in a given position were recognized by peptide-specific Th clones raised from some individuals, but not from others. We show that this is due neither to individual modes of processing nor to the use of distinct major histocompatibility complex MHC class II restriction elements, but rather that it is related to the fine specificity of the clones. To study the effect of epitope context on selection of T cell repertoire in a naive individual, T cell lines were generated in vitro by stimulation with different peptide constructs. This resulted in the induction of diverse clonotypes defined by the pattern of recognition of different constructs, by T cell receptor V beta gene usage and by fine epitope mapping.

Spontaneous bacterial empyema in cirrhotic patients: a prospective study

Spontaneous bacterial empyema (SBEM) is an infection of a preexisting hydrothorax in cirrhotic patients and has seldom been reported. To determine its incidence and primary characteristics, all cirrhotic patients with pleural effusion underwent thoracentesis at our hospital either on admission or when an infection was suspected. Pleural fluid (PF) study included biochemical analysis, polymorphonuclear (PMN) leukocyte count, and culture by two methods: conventional and modified (inoculation of 10 mL of PF into a blood culture bottle at the bedside). SBEM was defined according to previously reported criteria: PF culture positive or PMN count greater than 500 cells/micro L, and exclusion of parapneumonic effusions. Sixteen of the 120 (13 percent) cirrhotic patients admitted with hydrothorax had 24 episodes of SBEM. In 10 of the 24 episodes (43 percent), SBEM was not associated with spontaneous bacterial peritonitis (SBP). PF culture was positive by the conventional method in 8 episodes (33 percent) and by the modified method (blood culture inoculation) in 18 (75 percent) (P = .004, McNemar). The microorganisms identified in PF were Escherichia coli in 8 episodes, Streptococcus species in 4, Enterococcus species in 3, Klebsiella pneumoniae in 2, and Pseudomonas stutzeri in 1. All episodes were treated with antibiotics without inserting a chest tube in any case. Mortality during treatment was 20 percent. We conclude that SBEM is a common complication of cirrhotic patients with hydrothorax. Almost half of the episodes were not associated with SBP; thus, thoracentesis should be performed in patients with cirrhosis, pleural effusion, and suspected infection. Culture of PF should be performed by inoculating 10 mL into a blood culture bottle at the bedside.

Prognosis assessment of cirrhotic patients with refractory ascites treated with a peritoneovenous shunt

OBJECTIVE

The role of peritoneovenous shunt in the management of refractory ascites has not been clearly established. The aim of this study was to determine readily accessible predictive survival factors in cirrhotic patients with refractory ascites treated with a peritoneovenous shunt.

METHODS

We studied a cohort of 100 cirrhotic patients with refractory ascites who underwent peritoneovenous-shunt placement in a university-based reference hospital.

RESULTS

The estimated median survival of patients after shunt placement was 11 months (95% CI, 7-14 months). Multivariate analysis based on the proportional hazards model disclosed four independent variables associated with poor survival: high Pugh score, nonalcoholic etiology, low ascitic fluid protein concentration, and history of spontaneous bacterial peritonitis.

CONCLUSIONS

Mortality of cirrhotic patients treated with a peritoneovenous shunt can be determined by a prognostic index using four easily available variables. Such a prognostic index, once prospectively validated, could be used as an adjunct in planning treatment of cirrhotic patients with refractory ascites.

A 17-kDa CD4-binding glycoprotein present in human seminal plasma and in breast tumor cells

We previously isolated gp17, a human seminal plasma glycoprotein, which specifically interacts with the D1-D2 region of CD4, a T cell surface molecule involved in antigen recognition mediated by helper T cells also acting as a receptor for the human immunodeficiency virus. In this study we report that monoclonal antibodies (mAb) reacting with gp17 are able to inhibit the binding of gp17 to immobilized soluble CD4. An immunohistochemical analysis shows that gp17 is also expressed in mammary tumor cells upon hormone treatment and in biopsies from breast cancer patients. A structural characterization of gp17, including amino acid sequencing, indicates that the protein has an extensive structural similarity with a glycoprotein designated as seminal actin-binding protein (SABP), also secreted by male sexual glands. SABP is in turn identical to gross cystic disease fluid protein-15 (GCDFP-15) or prolactin-inducible protein (PIP), a factor known as a highly specific and sensitive marker of primary and metastatic apocrine breast cancer. To establish further the correspondence of gp17 and GCDFP-15/PIP/SABP, the latter was expressed in bacteria from a cloned cDNA and purified by affinity chromatography to either anti-gp17 mAb-Sepharose or CD4-Sepharose. The purified recombinant protein is shown to inhibit the binding of labeled, pure g17 to immobilized soluble CD4. The finding that breast cancer cells express a protein able to interact with the CD4 domains involved in the recognition of class II major histocompatibility antigens suggests a possible mechanism by which a tumor may affect the activity of tumor-infiltrated CD4+ T cells.

Minimal sequence requirements for synthetic peptides derived from the V3 loop of the human immunodeficiency virus type 1 (HIV-1) to enhance HIV-1 binding to cells and infection

We previously demonstrated that a 23-mer peptide (DB3) derived from the V3 loop of the surface glycoprotein of HIV-1 MN strain was able to bind to soluble CD4 and enhance HIV-1 infection. The mechanism and structural features required for these biological activities were studied by using shortened DB3 derivatives and DB3 analogs carrying single amino acid substitutions. We found that peptides in which the aromatic amino acid in position 15 or 16 had been replaced by an uncharged hydrophobic residue (DB3-I15 and DB3-I16), analogs in which positively charged amino acids were replaced by corresponding D-enantiomers, and shortened DB3-derivatives lost both enhancing activity and ability to bind to soluble CD4. Other peptide variants in which a positively charged amino acid was replaced by asparagine at positions 3 (DB3-N3), 6 (DB3-N6), and 19 (DB3-N19), respectively, retained both enhancing and binding activities, although with different efficiencies. The CD4 binder peptides DB3 and DB3-N19, but none of the CD4 nonbinder peptides, enhanced CD4 expression on peptide-treated cells as well as gp120 binding to both CD4+ cells and soluble CD4. These findings strongly suggest that the peptide/CD4 interaction induced an increase in both CD4 expression and CD4/gp120 binding affinity, which in turn mediated the enhancement of viral infection. A model of the structural conformation of DB3 peptide required for its biological activities is discussed.

Competition of HLA-DR and a beta 2 domain peptide for HIV envelope glycoprotein gp120 binding to CD4

HLA class II molecules and the HIV envelope glycoprotein gp120 are ligands of CD4. Reciprocal interaction sites have been well characterized for gp120 and CD4, but require further definition for HLA class II and CD4. A major CD4 binding site encompassing amino acids 134-148 in the beta 2 domain of HLA-DR has been previously identified. Recently, we have shown, by extensive characterization of mutated CD4 molecules expressed in COS cells, that HLA class II antigens interact mainly through the HIV gp120 binding site and possibly through a second minor interaction site mapping on the same face of the molecule. Based on the direct binding in vitro of iodinated affinity-purified HLA-DR1 molecules to polystyrene immobilized human IgG3-CD4, we now report on reciprocal binding inhibition of gp120, HLA-DR1 and the DR beta 2 synthetic peptide to CD4. The results strongly suggest that gp120 and the beta 2 region (amino acids 134-148) of HLA-DR1 bind mainly to the same part of CD4 domain 1 and that the CD4 binding site of HLA-DR requires the existence of a class II homodimer. In that case, alpha 2 chain residues might interact with CD4 residues different from those involved in the binding of gp120 but located close to them in the first domain.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term culture and T cell receptor analysis of T cell clones isolated from a patient with adenosine deaminase deficiency and type I diabetes

We performed limiting dilution culture of T cells from a patient affected by primary immunodeficiency as a result of complete lack of adenosine deaminase (ADA) activity and also affected by insulin-dependent diabetes mellitus (type I diabetes). Despite the occurrence of immunodeficiency, we were able to raise and grow T cell clones derived from this patient in long-term culture. These T cells displayed ADA enzymatic activity and produced interleukin-2 after engagement of their T cell receptor (TCR)/CD3 complex. We analyzed the TCR repertoire of such clones by nucleotide sequencing of TCR beta chains. The results show that the T cell clones express different V beta but similar J regions. However, the CDR3 regions which are implicated in antigen recognition were found to be heterogeneous.

Control of nucleo-cytoplasmic HLA-DRA mRNA partitioning by interaction of a retention signal with compartmentalized proteins

Transport of mRNA from the nucleus to the cytoplasm is still a poorly understood process in which RNA signal sequences and cognate RNA-binding proteins may be involved. We have analysed the transport of the mRNA encoded by HLA-DRA, a member of the immunologically important MHC class II multigene family. We report that, in transient transfection experiments, HLA-DRA mRNA molecules encompassing a signal situated in the 3' untranslated region predominantly accumulate in the nucleus. We also show that the RNA sequence involved interacts with compartmentalized proteins of either nuclear or cytoplasmic origin. Deletion of the mRNA region encompassing this retention site results both in the abrogation of protein binding and in the release of HLA-DRA mRNA into the cytoplasm. In addition, we have found that the distribution of these HLA-DRA mRNA binding proteins is different in different cell types; in particular, their pattern of expression in Ntera-2, a human teratocarcinoma cell line, is distinct from that observed in Raji, a human B-lymphoma cell line, and is modulated by growth in retinoic acid. We conclude that recognition of a mRNA retention signal by proteins located in different compartments on either side of the nuclear membrane may regulate the nucleo-cytoplasmic partitioning of HLA-DRA transcripts and, perhaps, of MHC class II mRNA in general.

RFLP characterization of the upstream regulatory region of the HLA-DQA1 gene

We have performed population and family studies of the distribution of DNA restriction length polymorphisms (RFLPs) in the 5' region of the HLA-DQA1 gene using a probe which corresponds to a sequence of the 5' flanking region of HLA-DQA1. Southern analysis detected four polymorphic fragments (X1, X2, X3 and X4) with XbaI and three fragments (E1, E2 and E3) with EcoRI. Family segregation studies showed that these RFLPs segregated in cis with the parental HLA haplotypes. Analysis of haplotypic associations of the X and E polymorphisms with each other and with HLA-DQA1 alleles demonstrates that DQA1 alleles can be further subtyped according to the particular XE combination which they carry. Hence, definition of these alleles provides new markers for HLA haplotyping and allows further splitting of otherwise identical DQA1 alleles. This information may be helpful for studies of association of disease susceptibility and autoimmunity with HLA haplotypes.

[Diagnosis and treatment of esophageal ulcers in patients seropositive for the human immunodeficiency virus (HIV-positive)]

Esophageal ulcers are often found in patients with human immunodeficiency virus infection. We have retrospectively reviewed the upper endoscopies performed in these patients during the last four years. 149 examinations were realized in 73 patients. Fourteen patients with esophageal ulcers were diagnosed. A severe immunological impairment was present in all patients (CD4 24.4 +/- 31.1 cells/ul). Symptoms were non-specific, with prevailing dysphagia and odynophagia. The etiological diagnosis was reached by histological studies and cultures in 5 cases (36%), three due to Herpes virus type I, one due to Cytomegalovirus and another one to Mycobacterium tuberculosis. Patients with multiple ulcers or small ones were successfully treated with antiviral drugs, even when the etiological studies were negative. Corticosteroids were useful in single and large ulcers in which diagnostic tests were negative.

Recognition of distinct HLA-DQA1 promoter elements by a single nuclear factor containing Jun and Fos or antigenically related proteins

The activity of MHC class II promoters depends upon conserved regulatory signals one of which, the extended X-box, contains in its X2 subregion a sequence related to the cAMP response element, CRE and to the TPA response element, TRE. Accordingly, X2 is recognized by the AP-1 factor and by other c-Jun or c-Fos containing heterodimers. We report that the X-box dependent promoter activity of the HLA-DQA1 gene is down-modulated by an array of DNA elements each of which represented twice either in an invertedly or directly repeated orientation. In this frame, we describe a nuclear binding factor, namely DBF, promiscuously interacting with two of these additional signals, delta and sigma, and with a portion of the X-box, namely the X-core, devoid of X2. The presence of a single factor recognizing divergent DNA sequences was indicated by the finding that these activities were co-eluted from a heparin-Sepharose column and from DNA affinity columns carrying different DNA binding sites as ligands. Competition experiments made with oligonucleotides representing wild type and mutant DNA elements showed that each DNA element specifically inhibited the binding of the others, supporting the contention that DBF is involved in recognition of different targets. Furthermore, we found that DBF also exhibits CRE/TRE binding activity and that this activity can be competed out by addition of an excess of sigma, delta and X-core oligonucleotides. Anti-Jun peptide and anti-Fos peptide antibodies blocked not only the binding activity of DBF, but also its X-core and sigma binding; this blockade was removed by the addition of the Jun or Fos peptides against which the antibodies had been raised. In vitro synthesized Jun/Fos was able to bind to all these boxes, albeit with seemingly different affinities. The cooperativity of DBF interactions may explain the modulation of the X-box dependent promoter activity mediated by the accessory DNA elements described here.

Structural studies on synthetic peptides from the principal neutralizing domain of HIV-1 gp120 that bind to CD4 and enhance HIV-1 infection

In previous studies we have demonstrated that synthetic peptides, corresponding to sequences in the (307-330) region of the gp120 principal neutralizing domain of different HIV-1 isolates are specifically recognized by a site distinct from the high affinity gp120-binding site of CD4. Interestingly, a peptide designed from the HIV-1 MN strain is able to enhance viral infection, while a HTLV-IIIB derived analogue is at least ten-fold less efficient and no effect is shown by other tested peptides. This enhancing effect occurs in the early step of infection and it is not strain restricted. A correlation between structure and biological functions evidenced by CD, FT-IR, and preliminary mono and bidimensional NMR is presented in this paper. The experimental data are compared to the predictions obtained by theoretical calculations.

Reversion of a transcriptionally defective MHC class II-negative human B-cell mutant

RJ2.2.5, a mutant derived from the human B-lymphoma cell, Raji, is unable to express the MHC class II genes because of a recessive transcriptional defect attributed to the lack of an activator function. We report the isolation of a RJ2.2.5 revertant, namely AR, in which the expression of the mRNAs encoded by these genes is restored. Comparison of the binding of nuclear extracts or of partially purified nuclear preparations from the wild-type, the mutant and the revertant cells to a conserved MHC class II promoter element, the X-box, showed no alteration in the mobility of the complexes thus formed. However, in extracts from RJ2.2.5, and other MHC class II negative cell lines, such as HeLa, the amount of complex observed was significantly higher than in wild-type Raji cells. Furthermore, the binding activity exhibited by the AR revertant was lower than that of the RJ2.2.5 and higher than that of Raji. The use of specific monoclonal antibodies indicated that in all cases c-Jun and c-Fos or antigenically related proteins were required for binding. An inverse correlation between the level of DNA-protein complex formed and the level of MHC class II gene mRNA expressed in the three cell lines was apparent, suggesting that overexpression of a DNA binding factor forming complexes with class II promoter elements may cause repression of MHC class II transcription. A model which reconciles the previously ascertained recessivity of the phenotype of the mutation carried by RJ2.2.5 with the findings reported here is discussed.

Identification of a CD4 binding site on the beta 2 domain of HLA-DR molecules

The CD4 and CD8 molecules are transmembrane glycoproteins expressed by functionally distinct subsets of mature T cells. CD4+ and CD8+ T cells recognize antigens on major histocompatibility complex (MHC) class II-bearing and class I-bearing target cells respectively. The ability of monoclonal antibodies against CD4 and CD8 to block antigen recognition by T cells, as well as cell-cell adhesion assays, indicate that CD4 and CD8 bind to nonpolymorphic determinants of class II or class I MHC. Here we demonstrate that soluble recombinant HLA-DR4 molecules from insect cells and HLA-DR-derived peptides bind to immobilized recombinant soluble CD4. CD4 binds recombinant soluble DR4 heterodimers, as well as the soluble DR4-beta chain alone. Furthermore, two out of twelve DR4-beta peptides could interact specifically with CD4. These findings show that CD4 interacts with a region of MHC class II molecules analogous to a previously identified loop in class I MHC proteins that binds CD8 (refs 8, 9).

Evidence of a natural killer (NK) cell repertoire for (allo) antigen recognition: definition of five distinct NK-determined allospecificities in humans

Previous studies indicated that CD3-CD16+ natural killer (NK) cells are capable of specific alloantigen recognition. Thus, alloreactive NK clones lysed normal allogeneic target cells (phytohemagglutinin [PHA] blasts) bearing the stimulating alloantigen but did not lyse autologous cells or the majority of unrelated allogeneic cells. In this study we investigated whether NK cells isolated from single individuals could exhibit different allospecificities. To this end, we derived large numbers of CD3-CD16+ clones (in the presence of PHA) from fresh CD3- peripheral blood lymphocytes. Cloning efficiencies ranged between 5 and 10%. The resulting CD3-CD16+ clones were tested for their reactivity against a panel of allogeneic PHA blasts (derived from six donors). In a given individual (A), four distinct groups of clones could be identified according to their pattern of reactivity (over 400 clones have been analyzed). Clones that could be assigned to one or another group of specificity represented 36% of all clones derived from this donor. The remaining clones did not display cytolytic activity against any of the allogeneic target cells used in the panel. None of the clones lysed autologous (A) PHA blasts, yet, these cells were lysed by the representative clones G10 and H12 specific for donor A. Clones displaying a cytolytic pattern of reactivity identical to that defined for donor A were present in other individuals studied, however not all groups of allospecific clones were necessarily represented in different individuals. Allospecific clones belonging to the various groups were homogeneous in the expression of EB6/GL183-triggering surface molecules, and could thus be assigned to one or another of the previously defined subsets of NK cells. Genetic analysis of the new NK-defined alloantigens was performed in representative families. The corresponding characters were found to segregate independently and, at least for three of them, an autosomic recessive type of inheritance could be demonstrated. Moreover, the comparative analysis of the segregation of the major histocompatibility complex haplotypes and the recessive or dominant alleles of the genes governing the five specificities analyzed indicated that there is no independent sampling between the two genetic traits, thus suggesting that the genes regulating the NK-defined specificities are carried by chromosome 6. Finally, some donors expressed more than one specificity, thus providing evidence for an NK-defined complex haplotype.

DNA polymorphisms in the 5'-flanking region of the HLA-DQA1 gene

The HLA-DQA1 gene exhibits haplotype-specific restriction fragment polymorphisms due to DNA rearrangements. We found that some of these polymorphisms extend into the 5' flanking region of the gene and are distinct from other HLA-DQA1 related DNA polymorphisms so far reported. Sequencing of genomic DNA subclones derived from the 5' flanking region of HLA-DQA1 showed the presence, in a DR4 haplotype, of two repetitive elements of the Alu family, oriented in opposite directions and bracketing an approximately 3 kilobase region immediately adjacent to the promoter of the gene. When DNAs extracted from several cell lines were analyzed by genomic hybridization using single-copy probes relative to these intervening sequences, polymorphisms were observed. No structural alterations of the gene immediately outside the DNA portion delimited by the two Alu elements were observed, thus suggesting that polymorphisms of the 5' end of HLA-DQA1 may be limited to the intervening region between the two Alu repeats. The latter includes upstream regulatory elements controlling the expression of the genes. The possibility that the structure of the DNA in this region may influence the regulation of HLA-DQA1 gene expression in different haplotypes is discussed.

Binding to CD4 of synthetic peptides patterned on the principal neutralizing domain of the HIV-1 envelope protein

The interaction between the viral envelope protein gp120 and the cellular surface antigen CD4 is a key event in HIV-1 infection. Reciprocal high affinity binding sites have been located in the first domain of CD4 and in the carboxy-terminal region of gp120, respectively. Upon infection, the membranes of the target cells fuse; sites of CD4 and gp120, distinct from their high affinity binding sites, play a role in the post-binding events leading to syncytia formation. We have studied the interactions of CD4 with gp120 and gp120-derived peptides using an in vitro assay based on immobilized recombinant soluble CD4 (sCD4). In this system CD4 binds to recombinant soluble gp120 and to anti-receptor peptides derived from the high affinity CD4-binding site of gp120, as well as to peptides corresponding to the principal neutralizing domain (PND) of the envelope protein, i.e., to the domain required for HIV-1-mediated syncytium formation. Competition experiments performed using epitope-specific mAbs and a variety of peptides indicated that PND-derived peptides are specifically recognized by a CD4 site adjacent to, but distinct from, the high affinity gp120-binding site of CD4. Synthetic peptides patterned on the PND of different viral isolates were retained onto sCD4-based affinity columns at different extent; some of the structural requirements for binding were analyzed. Studies performed on CD4+ T-cells showed that PND-derived peptides also interact with CD4 in its native membrane-bound conformation. These results indicate that a direct contact takes place between CD4 and the gp120 domain participating in HIV-induced syncytia formation.

Interaction of seminal plasma proteins with cell surface antigens: presence of a CD4-binding glycoprotein in human seminal plasma

We report in this paper the presence in the human seminal plasma of a glycoprotein capable of binding to CD4, a surface antigen expressed on the surface of T-cells, macrophages, and sperm cells, which acts as a coreceptor in antigen-mediated T-cell activation and as a receptor for the AIDS virus, HIV-1. This protein, namely gp17 (apparent MW = 17,500 Da), was purified by affinity chromatography and characterized by SDS/PAGE analysis. Its binding to CD4 was inhibited by anti-CD4 mAbs directed against V1, a region of CD4 implicated in the binding to MHC class II antigens and to the HIV-1 envelope protein gp120, but not by mAbs directed against other CD4 determinants. The presence of a CD4-masking factor in human seminal plasma may be relevant to the modulation of maternal immunity at insemination and to the control of sexual transmission of HIV-1.