Cholesterol efflux from macrophages mediated by high-density lipoprotein subfractions, which differ principally in apolipoprotein A-I and apolipoprotein A-II ratios.

High-density lipoprotein (HDL) was fractionated by preparative isoelectric focussing into six distinct subpopulations. The major difference between the subfractions was in the molar ratio of apolipoprotein A-I to apolipoprotein A-II, ranging from 2.1 to 0.5. The least acidic particles had little apolipoprotein A-II, were larger and contained the most lipid. The efflux capacity of the HDL subfractions was tested with mouse peritoneal macrophages and a mouse macrophage cell line (P388D1), either fed with acetylated low-density lipoprotein or free cholesterol. All the HDL subfractions were equally able to efflux cholesterol. The efflux was concentration dependant and linear for the first 6 h. The HDL subfractions bound with high affinity (Kd = 6.7-7.9 micrograms/ml) at 4 degrees C to the cell surface of P388D1 cells (211,000-359,000 sites/cell). Ligand blotting showed that all the HDL subfractions bound to membrane polypeptides at 60, 100, and 210 kDa. These HDL binding proteins may represent HDL receptors. In summary HDL particles, which differed principally in ratio of apolipoprotein A-I to apolipoprotein A-II behaved in a similar manner for both cholesterol efflux and cell surface binding.

Differential expression of surface membrane growth hormone receptor on human peripheral blood lymphocytes detected by dual fluorochrome flow cytometry.

Although several reports indicate proliferative and functional effects of human GH (hGH) on peripheral blood lymphocytes (PBL), no information is available about hGH receptor (GHR) expression in PBL subsets. Here, the surface membrane GHR levels were investigated in different human PBL subpopulations using a fluorescein isothiocyanate (FITC)-conjugated monoclonal antibody specific for the GHR (mAb263) in dual fluorochrome flow cytometric assays. Strong GHR expression was found in B-cells (CD20+), whereas CD2+ lymphocytes, including T-cells as well as natural killer cells, exhibited considerably lower levels of receptor expression. Similarly, using FITC-labeled recombinant hGH, receptor expression on CD20+ cells was significantly higher than that on CD2+ cells. Abundant expression of GHR in B-lymphocytes was confirmed by reverse transcriptase-polymerase chain reaction analysis of GHR messenger ribonucleic acid from isolated B-cells. Accordingly, the B-cell merits greater consideration as a GH target cell. The use of FITC-labeled mAb263 and hGH is of potential use for the study of GHR levels in patients exhibiting different types of growth disorders. Because of its high specificity for GHR, FITC-labeled mAb263 is also of considerable value for specifically demonstrating the presence of GHR, because hGH may interact with and act through PRL receptor, as shown previously in human neutrophils.

A novel monoclonal antibody recognizing human thymocytes and B-cell chronic lymphocytic leukemia cells.

This paper describes a new murine monoclonal antibody, UN5, raised against human thymocytes. This antibody recognizes a molecule of approximately 45 kDa on thymocytes. Flow cytometric analysis reveals a high intensity of labeling with the majority of thymocytes, whereas only CD20+ cells from peripheral whole-blood samples are weakly stained. Peripheral T cells, granulocytes, platelets and red blood cells do not express this antigen, while monocytes are only weakly labeled by UN5. Furthermore, the UN5 antibody discriminates between different types of B-cell malignancies, reacting with a subgroup of B-cell chronic lymphocytic leukemias and hairy cell leukemias, but not with the other kinds of hematopoietic malignancies tested. Antibody UN5 should prove a useful tool for the study of T-cell precursors and for analysis of both normal and neoplastic B cells.

Characterization of soybean endopeptidase activity using exogenous and endogenous substrates.

Endopeptidase activity in mature soybean seeds (Glycine max), has been measured using an exogenous substrate, [(125)I]iodoinsulin B chain. On the basis of pH optimum and the use of specific proteinase inhibitors, two distinct endopeptidase activities can be identified in both the embryonic axis and the cotyledons. One activity is characteristic of a neutral/alkaline metalloendopeptidase(s) and the other of an acidic carboxylendopeptidase(s). Neither activity is membrane-bound. The metalloendopeptidase(s), most probably working with neutral expopeptidases also present in the tissues, is capable of degrading certain subunits of the storage proteins. The beta subunit of conglycinin and additional seed polypeptides remain resistant to degradation. The carboxylpeptidase activity displayed a different specificity towards endogenous substrates; in particular, an acid-soluble polypeptide of apparent molecular weight 30,000 appeared to be the principal substrate for limited proteolytic degradation by the proteinase(s). Soybean agglutinin remained resistant to degradation by either class of endopeptidases.

Interactions of soya-bean agglutinin with purified glycoconjugates and soya-bean seed components.

A radioaffinity assay for lectin binding to receptors was developed and characterized by using the interactions between soya-bean agglutinin and four glycoconjugates, namely thyroglobulin, galactomannan, fetuin and asialofetuin. On application of the assay to soya-bean extracts a wide range of seed components were found to have the capacity to interact with soya-bean agglutinin. These included both trichloroacetic acid-soluble and trichloroacetic acid-insoluble glycoconjugates and two classes of particulate matter distinguished by their differential solubility in Triton X-100.

Characterization and purification of proteins which bind high-density lipoprotein. A putative cell-surface receptor.

High-density lipoprotein (HDL) is shown by ligand blotting to bind membrane-associated polypeptides with sizes of 60, 100 and 210 kDa. Binding was concentration-dependent and competed by excess unlabelled HDL. All the major apolipoproteins of HDL, apoA-I, apoA-II and apoA-IV, bound independently. The 100 kDa and 210 kDa HDL-binding activities were purified from membranes of Hep3B tumour cells by ion-exchange chromatography and gel filtration. The binding activities at 100 kDa and 210 kDa co-purified. After treatment with disulphide-reducing reagent, the 210 kDa band was no longer present and an increase was observed in the amount and binding ability of the 100 kDa polypeptide. The 100 kDa binding protein labelled at the cell surface with 125I could be immunoprecipitated after cross-linking to cell-surface-bound HDL. It is proposed that this HDL-binding activity, a putative cell-surface receptor for HDL, exists totally or in part as a high-molecular-mass complex composed of 100 kDa subunits.

A recombinant apoA-1--protein A hybrid reproduces the binding parameters of HDL to its receptor.

We have constructed a plasmid, pLM8, containing the coding sequence of the mature human apoA-1 fused to the coding sequence of the IgG-binding domains of protein A (PA) from Staphylococcus aureus. The hybrid gene is transcribed in Escherichia coli under the control of a heat-sensitive repressor, leading to the synthesis of large amounts of hybrid protein (apoA-1--PA). The hybrid protein was purified by denaturation with urea and alkali, renaturation and affinity chromatography on an IgG Sepharose column. ApoA-1--PA is soluble and has an Mr of 316 kd, as determined by gel filtration. This is five times the monomer size of 62 kd, predicted from the sequence and found by SDS-PAGE analysis. Cell surface binding activity of the hybrid protein was tested using two different cell types (J774 macrophages and Fao hepatocytes) and compared to human high density lipoprotein (HDL). High-affinity binding was found for both ligands in both cell lines (Kd = 3.4 X 10(-8)M in Fao cells, 4.9 X 10(-8) M in J774 cells for apoA-1--PA and 3.0 X 10(-8) M in Fao cells, 2.8 X 10(-8) M in J774 cells for HDL), with approximately 2 X 10(5) high-affinity binding sites per cell. ApoA-1--PA and HDL effectively competed with each other for binding to the cell surface. Additionally, they both bound to a 110-kd polypeptide on a ligand blot, identifying an HDL receptor. The binding parameters of HDL were very similar to those of apoA-1--PA.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and characterization of a T cell growth inhibitory factor produced by K562 erythromyeloid cells.

Cells of the human erythroleukemia cell line K562 constitutively secrete a factor that inhibits human T lymphocyte proliferation induced via CD3/Ti. The factor, termed K-TIF (K562-derived T cell inhibitory factor) is produced in either the presence or absence of fetal calf serum in cultures of K562 cells and can be precipitated by 70% NH4SO4. Gel filtration chromatography on Superose 12 resin by FPLC showed that the inhibitory factor has a molecular weight of approximately 30-35 kDa. A protein of this size, metabolically labeled with [35S]methionine, specifically bound human peripheral blood mononuclear cells. Chromatofocusing with Mono P by FPLC (pH gradient 7.2-5) indicates that the inhibitory factor has an isoelectric point of 6.0-6.4.

Differential regulation of the expression of interleukin-2 receptor gamma-chain during the in vitro differentiation of human myeloid cells.

The common gamma-chain (gamma c) is a shared component of cell-surface receptors for the interleukins- 2, -4 and -7, and possibly others. We studied its expression in cells and cell lines of myeloid origin and found ubiquitous presence of gamma c mRNA in all cells examined. Differential regulation of gamma c expression was observed in myeloid cell lines induced to differentiate in vitro. In K-562 erythromyeloid cells, a sharp rise in the levels of gamma c mRNA and protein accompanied megakaryocytic, but not erythroid, differentiation. Surface binding of interleukin-2, as well as the transcripts for cognate receptor chains, were scarcely detectable in K-562 cells, whereas a significant increase in the binding of granulocyte-macrophage colony-stimulating factor specifically occurred during their megakaryocytic maturation. Our data indicate that expression of gamma c is a common feature of human myeloid cells, and suggest that its expression may be a requirement for human myelopoiesis.

Expression of growth hormone receptor by peripheral blood lymphocytes in children: evaluation in clinical conditions of impaired growth.

OBJECTIVE: It is widely accepted that the haematopoietic system is a target of growth hormone action and that GH may act as a lymphokine. The expression of GH receptors (GHR) on human peripheral blood lymphocytes (PBL) has been reported previously in adult donors by dual fluorochrome flow cytometry. The aim of this study was to apply the cytofluorimetric method to the analysis of GHR expression on PBL in various human conditions characterized by different patterns of growth due to age or physiopathological conditions. SUBJECTS AND DESIGN: PBL from 38 normal (control) subjects (7 newborns, 18 prepubertal children, 13 adults) were studied in order to provide age-related physiological data. Twenty-two short children (18 with idiopathic short stature, 4 with Ullrich-Turner syndrome) were studied to determine the expression of GHR in conditions of impaired longitudinal growth which may or may not require GH treatment. METHODS: Analysis was performed using a fluorescein isothiocyanate (FITC)-conjugated antibody specific for the GHR (mAb263) and phycoerythrin (PE)-anti CD2 (T and natural killer cells) or PE-anti CD2 (B cells) in dual fluorochrome flow cytometric assays. Results were expressed as mean fluorescent intensity (MFI). RESULTS: Adult CD2+ coils exhibited a significantly higher GHR expression (MFI 347 +/- 40) than that expressed in children and newborns (MFI 285 +/- 36 and 299 +/- 41, respectively, P < 0.001). A significantly increased expression of GHR on CD2+ cells was also found in short children (MFI 330 +/- 42 vs 285 42- 36, respectively; P < 0.002), whereas Ullrich-Turner syndrome patients did not show any difference from their age and gender matched controls (254 +/- 52 and 288 +/- 40, respectively). A negative relationship was found between GHR expression on CD2+ cells and height-SDS (r - 0.54, P < 0.0001) or BMI (r - 0.4, P < 0.015) in controls and short children, independent of their GH secretory status. Expression of GHR and CD20+ cells was higher than that expressed on CD2+ cells in all subjects. No appreciable differences were found in the MFI levels of GHR expression on CD20+ cells either among the different age group controls or between short children or Ullrich-Turner syndrome patients. A significant downregulation of expression was shown in CD20+ (P < 0.008) but not CD2+ cells after 6 months of GH treatment in 6 short children who had a poor response to GH provocative tests. CONCLUSIONS: GH receptor expression on immune cells in non-syndromic short children appears to be inversely related to the linear growth expression and BMI of the subjects, contrary to findings with hepatic derived serum GHBP. This finding may reflect alternate exon usage in lymphoid cells, and indicates that GH has a distinctive role in the immune system.

CD36 is rapidly and transiently upregulated on phytohemagglutinin (PHA)-stimulated peripheral blood lymphocytes. Analysis by a new monoclonal antibody (UN7).

The monoclonal antibody (mAb) UN7, clustered as an anti-CD36 mAb, has been used to test the cell surface expression of CD36 on peripheral blood lymphocytes (PBL) following mitogenic stimulation. CD36, scarcely expressed on resting cell membranes, was rapidly upregulated on PBL after phytohemagglutinin (PHA) stimulation. The antigen was detected on the cell surface after 15 min of stimulation, increased rapidly by 60 min and peaked between 3 and 12 h, declining thereafter. The inhibition of protein synthesis by cycloheximide did not modify the PHA-induced expression of CD36. Neither the anti-CD3 OKT3 mAb nor the anti-CD2 BIL 2.29 and 9.1 mAbs induced any significant upregulation of the molecule. The addition of anti-CD28 15E8 mAb or IL-2 or IFN-gamma to PHA or anti-CD3 or anti-CD2 mAbs did not influence the pattern of CD36 expression. The phorbol-2-myristate-13-acetate (PMA), alone or in combination with ionomycin, was unable to activate the expression of CD36, while it inhibited the PHA-induced upregulation. The PHA-induced upregulation of CD36 was partially inhibited by the addition of LY294002 or wortmannin, while not affected by that of calphostin C. Thus, CD36 was found to be early and transiently upregulated by PHA stimulation on PBL. The rapid modulation of the molecule was not related to new protein synthesis, but was probably due to the insertion into the plasma membrane of a presynthetized protein pool.

Purification and characterization of a human sialoglycoprotein antigen expressed in immature thymocytes and fetal tissues.

The monoclonal antibody UN1 was previously produced in our laboratory on the basis of selective reactivity with human thymocytes and has been classified as unclustered by the 5th and 6th International Workshop and Conference on Human Leukocyte Differentiation Antigens. The antigen recognized by mAb UN1 was found to be expressed on the cell surface of immature human thymocytes, a subpopulation of peripheral T lymphocytes and on several fetal tissues including thymus. The UN1 antigen is purified from children's thymus by ion-exchange and affinity chromatography. Two-dimensional electrophoresis shows that the purified antigen displays microheterogeneity appearing as multiple spots over a pI range 4.4-5.0 at 100-120 kDa. Treatment with neuraminidase results in a retarded migration in SDS-PAGE, an increase in isoelectric point and a reduction in carbohydrate content, indicating a substantial content of sialic acid. Glycosidase digestion and lectin-binding analysis indicate that the carbohydrate residues are essentially O-linked. A preliminary analysis has detected the UN1 antigen in human breast carcinoma tissues but not in normal breast. The biochemical features and the pattern of expression of the UN1 antigen indicate that this molecule may have the characteristics typical of the family of cell-membrane-associated mucin-like glycoproteins; a number of these molecules are thought to have a role in cell-cell interaction, tumor progression and metastasis.

Regulation of cell survival in CD95-induced T cell apoptosis: role of NF-kappa B/Rel transcription factors.

The activity of NF-kappa B/Rel transcription factors can inhibit the apoptosis induced by TNF, UV or cancer therapy drugs in a number of cell types, including human T lymphocytes. Furthermore, the NF-kappa B/Rel inducer, phorbol-12-myristate-13-acetate (PMA), has been reported to suppress the CD95-induced apoptosis of human T lymphocytes. To verify whether the survival-enhancing effect of PMA required NF-kappa B/Rel activity, we generated two Jurkat cell sublines (AL.7 and AL.8) transfected with a pCMV4-I kappa B alpha construct, and two (AL.3 and AL.5) with the void pCMV4 vector. Compared to wild type, AL.3 and AL.5 cells, the AL.7 and AL.8 sublines displayed markedly lower amounts of NF-kappa B/Rel nuclear complexes and a reduced expression of a kappa B-controlled CAT reporter gene after 1 and 4 h of incubation with PMA, respectively. All the five cell types displayed negligible levels of apoptosis when cultured with medium or PMA alone; when stimulated with the mAb CH-11, the AL.7 and AL.8 sublines displayed apoptotic responses only slightly (<0.5 fold) higher than control cells. On the other hand, the salvage activity of PMA was partially impaired in the AL.7 and AL.8 sublines. PMA inhibited apoptosis by >85% in wild type, AL.3 and AL.5 cells and by <60% in the AL.7 and AL.8 sublines; the apoptosis percentages in the mAb CH-11 + PMA cultures of the I kappa B alpha-transfected cells were >4-fold higher than in control cells. We conclude that the inhibition of the CD95-induced apoptosis by PMA relies on both NF-kappa B/Rel-dependent and -independent mechanisms. The partial contribution of these nuclear factors to the suppression of apoptosis indicates that the NF-kappa B/Rel activity can influence the extent of the CD95-induced T cell death.

XbaI polymorphism of the apolipoprotein B gene in patients with hyperlipidemia and echo-Doppler evidence of arterial lesions.

This study was designed to assess whether the XbaI restriction fragment length polymorphism (RFLP) for apolipoprotein B (apo B) gene could be related with a genetic predisposition to develop hyperlipidemia and atherosclerosis. Relationships between XbaI RFLP and serum cholesterol were evaluated by comparing hyperlipidemic patients with healthy controls. Statistical analysis (chi-square test) showed no significant difference in either genotype distribution or allele frequencies. Hyperlipidemic patients were then divided according to triglycerides, either above or below 200 mg/dl and XbaI genotype frequencies were measured. No significant differences in genotype distribution or allele frequencies were found. The hyperlipidemic patients were tested for the presence of arterial disease by echo-Doppler and angina questionnaire. The XbaI genotype frequencies were determined in patients with arterial disease and compared to those without evidence of disease. No significant differences were found between the two groups.

Identification by differential display of transcripts regulated during hematopoietic differentiation.

The polymerase chain reaction-based differential display method (DDRT-PCR) was used to identify mRNAs differentially expressed during the maturation of human CD34+ progenitor cells stimulated to differentiate in vitro towards granulomonocytic or erythroid lineages with a mixture of hemopoietins (kit ligand + interleukin 3 + GM-CSF in the absence or presence of erythropoietin, respectively). Three cDNA transcripts (B32, B41, and B56) display differential expression during cytokine-induced maturation of CD34+ cells. These clones have no homology with already-described sequences. Primer extension cofirmed the presence of the corresponding mRNA. The levels of mRNA corresponding to B32 are enhanced in the later phases of the granulomonocytic as well as in the erythroid differentiation of CD34+ cells. The mRNA identified by B41 was induced by a late stage in only granulomonocytic differentiation of CD34+ cells. The mRNA corresponding to B56 was instead present in nonstimulated CD34+ cells, declined in the early stages of differentiation, and reappeared at later stages in cells treated with both combinations of cytokines. Expression of these genes was detected in a number of acute myelogenous leukemias, as well as in some leukemic cell lines. B32 and B41 were downregulated in KG-1 cells induced to differentiate towards the monocytic lineage, whereas the levels of B56 were unchanged. In K562 cells, clones B41 and B56 were downregulated only in the late phases of PMA-induced megakaryocytic differentiation and during erythroid differentiation. B32 was rapidly downregulated when K562 cells were induced to differentiate towards either megakaryocytic or erythroid phenotypes. These transcripts represent novel hematopoietic cDNAs that should prove of value for the study of human blood cells and their disorders.

A 5' regulatory sequence containing two Ets motifs controls the expression of the Wiskott-Aldrich syndrome protein (WASP) gene in human hematopoietic cells.

The recently-identified Wiskott-Aldrich syndrome protein gene (WASP) is responsible for the Wiskott-Aldrich X-linked immunodeficiency as well as for isolated X-linked thrombocytopenia (XLT). To characterize the regulatory sequences of the WASP gene, we have isolated, sequenced and functionally analyzed a 1.6-Kb DNA fragment upstream of the WASP coding sequence. Transfection experiments showed that this fragment is capable of directing efficient expression of the reporter chloramphenicol acetyltransferase (CAT) gene in all human hematopoietic cell lines tested. Progressive 5' deletions showed that the minimal sequence required for hematopoietic-specific expression consists of 137 bp upstream of the transcription start site. This contains potential binding sites for several hematopoietic transcription factors and, in particular, two Ets-1 consensus that proved able to specifically bind to proteins present in nuclear extracts of Jurkat cells. Overexpression of Ets-1 in HeLa resulted in transactivation of the CAT reporter gene under the control of WASP regulatory sequences. Disruption of the Ets-binding sequences by side-directed mutagenesis abolished CAT expression in Jurkat cells, indicating that transcription factors of the Ets family play a key role in the control of WASP transcription.