Familial hypercholesterolemia (FH) has a frequency of 0.2% in most populations of the world. In selected populations such as the Afrikaners in South Africa, the Christian Lebanese, and the French Canadians, the disease is more frequent due to the founder effect. Previous studies demonstrated that a single mutation at the LDL receptor locus, the so-called French Canadian deletion, makes up 60% of the mutant genes responsible for FH in the French Canadian population. In this study, efforts were directed to determine if there were other common LDL receptor mutations in this population. Three missense mutations were identified and each mutation was reproduced and expressed in vitro. Two of the three mutations result in the production of an LDL receptor protein that is not processed to its mature form at a normal rate. Molecular assays were developed to detect the mutations directly, and the LDL receptor genes of 130 French Canadian FH heterozygotes were screened for the presence of the three missense mutations as well as two deletions. LDL receptor mutations were detected in 76% of individuals and 14% had one of the three missense mutations.
E Leitersdorf, E J Tobin, J Davignon, H H Hobbs
Antigen-antibody complexes were made from allergens of the common house dust mite, Dermatophagoides pteronyssinus (Dpt) and an excess of purified autologous specific antibodies. These complexes have been used to treat Dpt-hypersensitive patients who suffered from chronic bronchial asthma. Clinical symptoms and medication intake were followed by filling in diary cards. Peak expiratory flow, measured four times a day, was also followed. Intradermal skin tests and bronchial challenge tests were performed with allergen together with an evaluation of nonspecific bronchial reactivity. Specific IgE and IgG antibodies were assayed after separation from the bulk of serum immunoglobulins by immunoadsorption. The study was carried out over two years according to a double-blind protocol. Intradermal inoculation of antigen-antibody complexes resulted in a marked reduction of both clinical and medication scores. No systemic side-effects were observed and only mild wheal and flare reactions were noted at the injection site. The treatment showed a drastic reduction of specific skin and bronchial reactivities with only marginal effects on nonspecific bronchial reactivity. Concentrations of specific IgE antibodies decreased significantly during the first weeks of treatment and remained at these lower values throughout the study. Specific IgG antibodies actually decreased in the majority of treated patients. The total amount of allergen used in this study was less than 1% of the amount currently used for conventional hyposensitization with the same allergen. These findings show that antigen-antibody complex inoculation is an efficient and safe means of treating allergic bronchial asthma and that the mechanism of action is likely to differ from conventional hyposensitization.
J J Machiels, M A Somville, P M Lebrun, S J Lebecque, M G Jacquemin, J M Saint-Remy
We developed a mouse model to compare the virulence of Campylobacter fetus strains with (S-plus) and without (S-minus) surface array protein (S-protein) capsules. In adult HA/ICR mice pretreated with ferric chloride, the LD50 for S-plus strain 84-32 was 43.3 times lower than its spontaneous S-minus mutant 84-54. Seven strains of inbred mice were no more susceptible than the outbred strain. In contrast to the findings with Salmonella typhimurium by others, 3 X 10(7) CFU of strain 84-32 caused 90% mortality in C3H/HeN (LPSn) mice and 40% mortality in C3H/HeJ (LPSd) mice. High-grade bacteremia in HA/ICR mice occurred after oral challenge with S-plus C. fetus strains and continued for at least 2 d, but was not present in any mice challenged with S-minus strains. Bacteremia at 30 min after challenge was 51.6-fold lower in mice pretreated with 10 microliters of rabbit antiserum to purified S-protein than after pretreatment with normal rabbit serum. Challenge of mice with a mixture of S-minus strain 84-54 and free S-proteins at a concentration 31.1-fold higher than found in wild-type strain 84-32 caused 30% mortality, compared with 0% with strain 84-54 or S-protein alone. These findings in a mouse model point toward the central role of the S-protein in the pathogenesis of C. fetus infection. The S-protein is not toxic per se, but enhances virulence when present on the bacterial cell surface as a capsule.
Z Pei, M J Blaser
Epidermal growth factor (EGF) exhibits specific saturable binding to cultured rat inner medullary collecting tubule cells and stimulates inositol trisphosphate (IP3) production by these cells in a dose-dependent fashion. EGF-stimulated IP3 production is enhanced by GTP gamma s or AIF4- and is inhibited by GDP beta s or pertussis toxin. Alterations in extracellular Ca2+ have no effect on either basal or EGF-stimulated IP3 production. Similarly, treatment with EGTA which decreases cytosolic Ca2+ is without effect. In contrast, treatment with ionomycin which increases cytosolic Ca2+ has no effect on basal IP3 production but enhances the response to EGF. Activation of protein kinase C inhibits IP3 production in response to either EGF or AIF4-. These studies demonstrate the occurrence of EGF-stimulated phospholipase C activity in the rat inner medullary collecting duct. Stimulation by EGF is transduced by a pertussis toxin-sensitive G protein, unaffected by alterations in extracellular Ca2+, insensitive to a decrement in cytosolic Ca2+, enhanced by an increase in cytosolic Ca2+, and inhibited by protein kinase C.
I Teitelbaum, A Strasheim, T Berl
The susceptibility to develop seropositive rheumatoid arthritis (RA) has been linked to specific genomic polymorphisms within the HLA complex. Two different haplotypes have been associated with the disease, HLA-DR1 and HLA-DR4. To investigate the link between such phenotypic disease associations and potential immune mechanisms we used alloreactive and antigen-specific human T cell clones. Here we describe a panel of alloreactive T cell clones directed to polymorphic determinants encoded by the third hypervariable region (hvr) of the HLA-DR beta 1-chain. T cell determinants defined by these clones are shared among HLA-DR1, HLA-Dw4, HLA-Dw13, HLA-Dw14, and HLA-Dw15, and are frequent in a population of RA patients. To study the role of such disease-associated epitopes in antigen-restricted T cell recognition we generated T cell clones from RA patients specific for mycobacterial antigens, Epstein-Barr virus antigens, and tetanus toxoid. In all three antigenic systems T cell clones were restricted to either HLA-DR1 or HLA-DR4. These data suggest that the polymorphisms within the first and second hvr of the HLA-DR beta 1-chain that are distinct in HLA-DR1 and HLA-DR4 and not associated with the disease are crucially involved in the recognition of antigens. Polymorphic determinants encoded by the third hvr are shared among disease-associated haplotypes and may function to mediate the interaction of alloreactive T cell receptor molecules with the HLA complex.
C M Weyand, J J Goronzy
Isovaleric acidemia (IVA) is caused by a genetic deficiency of isovaleryl-CoA dehydrogenase (IVD). At least five distinct variant IVD alleles are known. We isolated five overlapping IVD cDNA clones from a human placenta cDNA library. They covered the entire coding region, except the initiation codon, and 587 bp in the 3'-noncoding region plus the poly(A) tail. The structure of the initiation site was identified by the study of genomic DNA and by the sequence comparison with rat IVD. Human IVD shared 89.6, 35.8, and 31.6% identical amino acid residues with rat IVD and human short and medium chain acyl-CoA dehydrogenases, respectively. In the Northern blot analysis of normal human liver and fibroblast poly(A)+ RNA, three mRNA species of different sizes (4.6, 3.8, and 2.1 kb) hybridized to IVD cDNA. Three mRNA species with similar sizes were also detected in five IVA fibroblast lines of different genotypes (variants 1, 1 X 2, 2, 3, and 5), suggesting that these variants are each due to a point mutation or small deletion.
Y Matsubara, M Ito, R Glassberg, S Satyabhama, Y Ikeda, K Tanaka
Intracellular ionized calcium has been strongly implicated in mediating several responses of human neutrophils to stimulation. However, proteins that serve as effectors of these responses have not been well characterized. To identify proteins that might serve as mediators of the effects of Ca2+ in human neutrophils, we isolated proteins that bind to membrane phospholipids in a Ca2(+)-dependent manner. The most abundant of these, a protein of 33 kD, was readily purified to homogeneity, and was found to bind to phosphatidylserine vesicles in the presence of 2 microM ionized Ca2+. In addition, this purified protein promoted Ca2(+)-dependent aggregation of isolated specific granules from human neutrophils, indicating that it might mediate membrane-membrane contact during processes such as phagosome-lysosome fusion or degranulation. This protein was localized to the cytoplasm of unstimulated neutrophils and found to account for approximately 1% of the cytosol protein. Amino acid sequence of several peptides derived from the purified protein revealed that it is identical to lipocortin III, a recently described member of the annexin family that is scarce in other cells and tissues. The abundance of this protein, together with its Ca2(+)-dependent membrane effects, suggest that it mediates membrane-localized events in stimulated neutrophils, such as phagosome-lysosome fusion or degranulation.
J D Ernst, E Hoye, R A Blackwood, D Jaye
Induction of human erythroleukemia (HEL) cells with nanomolar tumor-promoting phorbol myristate acetate (PMA) diesters results in the synchronous acquisition of multiple markers of the megakaryocyte phenotype. Induced cells markedly increase their content of cytoplasm and show features of morphological maturation. At the ultrastructural level, PMA-treated cells show increases in cytoplasm, nuclear lobulation and nucleolar content, and free ribosomes. Limited numbers of cells also express alpha-granules and nascent demarcation membrane systems. Functionally, PMA-stimulated HEL cells express increased amounts of the megakaryocyte/platelet proteins: glycoprotein IIb/IIIa, platelet factor 4, von Willebrand factor, glycoprotein Ib, and thrombospondin. No changes are observed in antigenic markers of the erythroid (glycophorin A) or macrophage lineages (MO-1 or MO-2). The increases in antigenic expression are rapid, reaching maximum levels within 3-4 d under serum-free conditions. Treatment with PMA also abruptly (within 1-2 d) inhibits cellular division in these cells. Washout studies indicate that phorbols exert their effect within 18-24 h, the approximate cell cycle time for these cells. Consistent with proliferative arrest, c-myc proto-oncogene transcripts begin to decline within 8 h of PMA treatment, although transcripts of c-myb are unaffected. Importantly, megakaryocyte differentiation is associated with endomitotic DNA synthesis (i.e., continued DNA synthesis in the absence of mitosis and cytokinesis), with HEL cells reaching a DNA content of 3-12 times that of unstimulated cells. Endomitosis is coordinately regulated with changes in antigenic expression and cell size such that those cells having the highest DNA content are the largest and also express the greatest levels of antigen.
M W Long, C H Heffner, J L Williams, C Peters, E V Prochownik
Nerve growth factor (NGF) is a polypeptide that is required for normal development and maintenance of the sympathetic and sensory nervous systems. Skin has been shown to contain relatively high amounts of NGF, which is in keeping with the finding that the quantity of NGF in a tissue is proportional to the extent of sympathetic innervation of that organ. Since the keratinocyte, a major cellular constituent of the skin, is known to produce other growth factors and cytokines, our experiments were designed to determine whether keratinocytes are a source of NGF. Keratinocyte-conditioned media from the keratinocyte cell line PAM 212 contained NGF-like activity, approximately 2-3 ng/ml, as detected by the neurite outgrowth assay. Freshly isolated BALB/c keratinocytes contained approximately 0.1 ng/ml. Using a cDNA probe directed against NGF, we demonstrated the presence of a 1.3-kb NGF mRNA in both PAM 212 and BALB/c keratinocytes. Since ultraviolet radiation (UV) is a potentially important modulating factor for cytokines in skin, we examined the effect of UV on NGF mRNA expression. Although UV initially inhibited the expression of keratinocyte NGF mRNA (4 h), by 24 h an induction of NGF mRNA was seen. The NGF signal could also be induced by phorbol esters. Thus, keratinocytes synthesize and express NGF, and its expression is modulated by UVB and phorbol esters.
V A Tron, M D Coughlin, D E Jang, J Stanisz, D N Sauder
Exposure of cultured endothelium to environments with low concentrations of oxygen, in the range of those observed in pathophysiologic hypoxemic states in vivo, compromises cellular barrier and coagulant function. An atmosphere with PO2 approximately 14 mm Hg was not lethally toxic to endothelial cultures, but cells became larger and exhibited small intercellular gaps. At low oxygen concentrations, passage of macromolecular tracers through hypoxic endothelial monolayers was accelerated in a time- and dose-dependent manner, presumably by a paracellular pathway via the gaps. Cell surface coagulant properties of the endothelium were also perturbed. At PO2 approximately 14 mm Hg thrombomodulin antigen and functional activity on the cell surface were diminished by 80-90%, and Northern blots demonstrated suppression of thrombomodulin mRNA. The decrease in thrombomodulin was twice as great compared with the general decline in total protein synthesis in hypoxia. In addition, expression of a direct Factor X activator developed under hypoxic conditions; the activator was membrane-associated and expressed on the surface of intact cultures, Ca-dependent, inhibited by HgCl2 but not PMSF, and had Km approximately 25 micrograms/ml for the substrate at pH 7.4. Synthesis of the activator was blocked by inclusion of cycloheximide, but not warfarin, in the culture medium. These results demonstrate that endothelial function is perturbed in a selective manner in the presence of low concentrations of oxygen, providing insights into mechanisms which may contribute to vascular dysfunction in hypoxemic states.
S Ogawa, H Gerlach, C Esposito, A Pasagian-Macaulay, J Brett, D Stern
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