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Biomedical subjects

J Guardiola

Publications and source records attributed to J Guardiola.

At least 19 recordsLinked to original sources
PubMed1992

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).

Amino Acid Sequence↗
PubMed1992

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.

Alleles↗
PubMed1992

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.

Base Sequence↗
PubMed1991

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.

Antibodies, Monoclonal↗
PubMed1991

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.

Amino Acid Sequence↗
PubMed1991

The molecular biology of MHC genes.

Antigenic peptides become associated with major histocompatibility complex (MHC) class I and class II surface antigens, are then presented to T cells and thereby elicit an antigen-specific cellular or humoral immune response. MHC molecules are genetically heterogeneous and polymorphic; their structure is therefore relevant to modulation of the immune system. The selective pressure resulting from this modulation is in turn the main driving force for the evolution of the complex genetic system. The density of MHC molecules on the cell surface is another parameter that influences immune responsiveness. The study of the evolution and regulation of MHC genes is, therefore, of great interest. These and other themes were discussed at the Third IIGB Workshop* which was recently held in Capri.

Animals↗
PubMed1990

Specific recognition of human CD3-CD16+ natural killer cells requires the expression of an autosomic recessive gene on target cells.

We analyzed the recently defined ability of CD3-CD16+ cells to specifically recognize and lyse normal allogeneic target cells (PHA-induced blasts). The susceptibility to lysis by a given alloreactive natural killer (NK) clone ("1 anti-A") was expressed by PHA blasts derived from 9 of 38 random donors analyzed. In all instances, the specific lysis of "susceptible" target cells was greater than 35% while that of "nonsusceptible" targets was less than 6% at an E/T cell ratio of 5:1. In addition to 1 anti-A, A anti-1 specific CD3-CD16+ clones could also be isolated from the reverse MLC combination. The relationship existing between lysis of normal allogeneic cells or tumor cells by the same CD3-CD16+ effector cell has been investigated: 1 anti-A specific CD3-CD16+ clones lysed PHA blasts of three of six cancer patients, while they lysed fresh tumor cells (ovarian carcinoma) from all six patients. The type of inheritance of the character "susceptibility to lysis" was analyzed in representative families. This analysis revealed that the character is inherited in an autosomic recessive fashion, and it is therefore different from MHC. We further investigated the type of segregation of the opposite character "resistance to lysis" (which is inherited in a dominant mode). The finding that this character segregated in all donors expressing given MHC haplotypes indicated that the gene regulating the expression of the NK-defined alloantigen is present on chromosome 6.

Antibodies, Monoclonal↗
PubMed1990

Spontaneous bacterial empyema in cirrhotic patients: analysis of eleven cases.

Eleven episodes of spontaneous bacterial empyema were identified in eight cirrhotic patients with ascites. Criteria for spontaneous bacterial empyema included positive pleural fluid culture or polymorphonuclear cell concentration greater than 500 cells/mm3, evidence of pleural effusion before an infectious episode and transudate characteristics during infection. In five cases, spontaneous bacterial empyema was culture-negative and was associated with spontaneous bacterial peritonitis. Ascitic fluid was culture-negative in two of these cases and culture-positive in three. Blood cultures were negative in all five of these cases. In six cases spontaneous bacterial empyema was culture-positive (Escherichia coli in four, Klebsiella pneumoniae in one and Clostridium perfringens in one). Four of these patients had the same organism in ascites; one had culture-negative spontaneous bacterial peritonitis and one had no infection of ascites. Blood cultures were positive in four of these patients; three died. Death was more frequent in patients with positive cultures than in those with negative ones (p less than 0.05). Patients with hydrothorax are prone to spontaneous bacterial empyema. This infection probably occurs through hematogenous seeding, but transfer of infected ascites from the abdominal cavity through the diaphragm cannot be excluded. Patients with spontaneous bacterial empyema may be asymptomatic or may be seen with fever, chills and dyspnea. Spontaneous bacterial empyema must be differentiated from parapneumonic empyemas. The presence of pleural effusion before the infectious episode, fluid characteristics and the organisms isolated are the clues for differential diagnosis. Treatment includes antibiotics; chest tube insertion probably is not necessary.

Adult↗
PubMed1990

A SINE insertion provides information on the divergence of the HLA-DQA1 and HLA-DQA2 genes.

The class II region of the human major histocompatibility complex (MHC) contains a cluster of highly polymorphic genes organized into at least three subloci (DR, DQ, and DP), each encoding a subset of surface antigens participating in the modulation of the immune response. Genetic diversity in this system is brought about by two major mechanisms, hypermutation and trans-species evolution. The DQ subregion contains a pair of closely related A genes, HLA-DQA1 and HLA-DQA2, whose phylogenetic relationship is uncertain, although their generation by duplication of an ancestral A gene before or after speciation can be implied. We report here the presence of a member of the Alu repetitive family immediately 5' to the HLA-DQA1 gene. The sequence of this element indicates that it may have integrated by transposition at the time of divergence of hominoids from Old World monkeys. HLA-DQA2 carries an empty integration target site in place of the Alu, thereby suggesting that the insertion of Alu near HLA-DQA1 was preceded by the separation of the two genes.

Animals↗
PubMed1990

Effect of the AIR-1 locus on the activation of an enhancerless HLA-DQA1 promoter.

Studies on the regulation of a major histocompatibility complex (MHC) class II gene, HLA-DQA1, in Ia-positive cells (Raji, a human B-lymphoma cell line) and in isogenic Ia-negative cells (RJ2.2.5, a mutant of Raji altered at the AIR-1 locus) are reported. As previously found, AIR-1 is required in its entirety for the activity of an enhancer factor, the absence of which abolishes transcription of MHC class II genes. In this paper, we show that HLA-DQA1 gene expression can be directed by an enhancerless promoter. The fact that this promoter is inactive in the RJ2.2.5 mutant suggests that the trans-acting element determined by the AIR-1 locus is not only an enhancer factor as previously described, but also acts at the MHC class II promoter level.

Base Sequence↗
PubMed1990

Susceptibility or resistance to lysis by alloreactive natural killer cells is governed by a gene in the human major histocompatibility complex between BF and HLA-B.

The specificity recognized on normal allogeneic cells by a given alloreactive (1-anti-A) natural killer clone is controlled by a gene locus termed EC1. Because the EC1 locus was previously shown to be located on chromosome 6, families characterized by a recombinant major histocompatibility complex haplotype were analyzed to map this locus more precisely. The breakpoint of recombination was studied by standard HLA typing, complement typing, and restriction fragment length polymorphism analysis of a series of genes located between the complement cluster genes and HLA-B within the major histocompatibility complex region. Three of 10 families analyzed were informative. From the data obtained, the EC1 locus maps between BF and HLA-B and presumably is one of the normal genes recently described in this region.

Antigens, Differentiation↗
PubMed1990

Comparison of two ascitic fluid culture methods in cirrhotic patients with spontaneous bacterial peritonitis.

The conventional method of ascitic fluid culture detects bacteria in only 50% of cirrhotic patients with neutrocytic ascites and suspected spontaneous bacterial peritonitis (SBP). We have prospectively compared two ascites culture methods in cirrhotic patients with spontaneous bacterial peritonitis: 1) conventional (on chocolate agar, blood agar, Mac Conkay agar, and thioglycolate broth), and 2) modified [inoculation of 10 ml of ascites in a tryptic soy broth (TSB) blood culture bottle at the patient's bedside]. In a 21-month period, 70 episodes of SBP were diagnosed according to our criteria in 60 cirrhotic patients. Both culture methods were performed simultaneously. The conventional grew bacteria in 40 episodes (57%), whereas the modified grew bacteria in 54 episodes (77%), a significantly higher sensitivity (p = 0.0001). In 16 cases (23%), ascitic culture was negative by both methods. The mortality rate was higher among patients with culture-positive SBP than those with culture-negative SBP (46% vs 37%), but did not reach statistical significance. We conclude that ascitic fluid inoculated into a TSB blood culture bottle at the patient's bedside should be used routinely for ascites culture in cirrhotic patients.

Ascitic Fluid↗
PubMed1989

Transcriptional and post-transcriptional regulation of human MHC class II genes require the synthesis of short-lived proteins.

We have studied the stability of protein factors which control the intracellular levels of human MHC class II genes in B cells. We report that human MHC class II gene transcription and mRNA stability require the synthesis of short-lived proteins which undergo rapid intracellular turnover. We found, in fact, that the amount of MHC class II mRNA produced by human B lymphoma or B lymphoblastoid cell lines abruptly decreased upon cultivation of cells in the presence of cycloheximide, a potent inhibitor of protein synthesis. Measurements of the rate of mRNA transcription in nuclei isolated from treated cells indicated that a cycloheximide-sensitive activator protein is needed to allow MHC class II mRNA transcription initiation. Likewise, comparison of mRNA turnover rate in cells treated with actinomycin D, an inhibitor of RNA synthesis, and in cycloheximide-treated cells shows that a post-transcriptional factor is required to stabilized human MHC class II mRNA by a factor of 8- to 10-fold in B cells. These results indicate that, along with the trans- and cis-acting factors required for transcriptional control, a series of signals must exist in B cells which implement a post-transcriptional level of regulation of MHC class II gene expression in B cells.

Cell Line↗
PubMed1988

An enhancer factor defect in a mutant Burkitt lymphoma cell line.

RJ 2.2.5 is an immunoselected mutant of the Burkitt lymphoma line Raji. It fails to display MHC class II antigens at the cell surface due to a transcriptional defect. We have identified the function of a regulatory factor that is defective in RJ 2.2.5 cells; this factor is absolutely required for the activity of an MHC class II gene enhancer.

DNA-Binding Proteins↗