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Q H Meng

Publications and source records attributed to Q H Meng.

29 records · Page 2Linked to original sources
PubMed1993

Apolipoprotein A-I domains involved in the activation of lecithin:cholesterol acyltransferase. Importance of the central domain.

The reaction of highly purified lecithin:cholesterol acyltransferase (LCAT) with defined reconstituted discoidal apoA-I-containing lipoproteins (LpA-I) with 2, 3, or 4 apoA-I molecules/particle (Lp2, 3, or 4A-I) has been studied in the presence of a number of specific anti apoA-I antibodies. Among nine anti-apoA-I monoclonal antibodies (mAbs) reacting with epitopes distributed over 80% of the sequence, three significantly inhibit the LCAT reaction with all particles. The position of their epitopes located in the middle to COOH-terminal region between residues 96-121 (3G10), 135-148 (A03), and 149-186 (A44) is compatible with an inhibition by steric hindrance over a central domain. Antibody 4H1 binding to the NH2 terminus (residues 2-8) profoundly increases (5-fold) the LCAT reaction with Lp2A-I (7.8 nm), but not with other particles. Other mAbs, A11 and 5F6, binding to epitopes (residues 99-139 and 118-141) enhance LCAT reactivity with the small Lp2A-I (7.8 nm) and Lp3A-I (10.8 nm) but not with their larger counterparts. Most mAbs have similar effects on LCAT reaction with native high density lipoprotein3 as with LpA-I. The inhibitory or enhancing effects of these mAbs are also observed with Fab fragments and not related to their binding affinity for apoA-I containing reconstituted lipoprotein particles. The intercalation of epitopes for mAbs that inhibit or enhance LCAT reaction with small LpA-I is compatible not with steric hindrance but with conformational modifications of apoA-I and indirectly of the lipids in small particles. We propose that enhancing mAbs act by stabilization of an apoA-I conformation which is not favored in small LpA-I, i.e. by increasing binding of amphipathic helices to lipids or by interfering with the mobility of a hinged domain. The epitopes for the inhibitory mAbs can be shown to overlap on several LpA-I models, indicating that steric hindrance over a single site is a possible mechanism of inhibition.

Antibodies, Monoclonal↗
PubMed1993

Apolipoprotein A-I conformation in discoidal particles: evidence for alternate structures.

To define the conformation of apolipoprotein A-I in discoidal particles, the immunoreactivity of a series of epitopes distributed along the apoA-I sequence has been evaluated in lipid-free apoA-I and in lipid-bound form. To this end, reconstituted discoidal lipoproteins, here called LpA-I, and defined by number of apoA-I per particle (e.g., Lp2A-I), have been prepared with palmitoyloleoylphosphatidylcholine, cholesterol, and apoA-I. Four LpA-I have been obtained and studied: two in the Lp2A-I class, 7.8 and 9.6 nm in diameter, and two in the Lp3A-I class, 10.8 and 13.4 nm. The immunoreactivity of all the epitopes tested was significantly different in LpA-I particles compared to lipid-free apoA-I, demonstrating that binding to lipids produces a drastic change in apoA-I conformation. Specific domains in the primary sequence become highly exposed while others are masked. Although the variation in immunoreactivity of the epitopes between various LpA-I was not drastic, significant differences in the calculated ED50 values were observed for a number of antibodies in small versus large particles within each class (Lp2A-I or Lp3A-I), indicating that particle size can modulate apoA-I conformation. In addition, when the competition between pairs of mAbs was analyzed in order to understand the relative position of epitopes, highly significant differences were observed as a function of particle size within each class. In particular, the competition between mAbs recognizing epitopes in the central region of apoA-I was greater in the larger particles than in their small counterparts.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗
PubMed1993

Etiological investigation of acute post-transfusion non-A, non-B hepatitis in China.

The etiology of acute post-transfusion hepatitis (PTH) non-A, non-B (NANB) in China was investigated with the combination of advanced techniques, including a second generation of enzyme immunoassay for detection of the antibodies to hepatitis C virus (anti-HCV), a reverse transcription and nested polymerase chain reaction (RT-nPCR) for HCV RNA, and a PCR for hepatitis B virus DNA. Of the 57 patients who were diagnosed as acute PTH-NANB, 46 (80.7%) were positive for anti-HCV and 41 (71.9%) had HCV RNA. Combining together, 53 (93.0%) were seropositive for anti-HCV and/or HCV RNA. Surprisingly, 18 of these with HCV markers were also positive for HBV DNA, although they were negative for HBsAg, suggesting that a portion of the patients with acute PTH NANB were coinfected by both HCV and HBV. In addition, 4 (7%) of the patients with acute PTH-NANB had no detectable HCV and HBV markers with the use of the above-mentioned techniques. These results indicate that etiologic agents(s) other than HCV and HBV may also cause acute PTH-NANB or that the current techniques may still not be sensitive enough to detect trace levels of HCV and HBV markers.

Adolescent↗
PubMed1992

Two distinct pathways of interferon induction as revealed by 2-aminopurine.

Activation and repression of IFN gene expression are controlled primarily at the transcriptional level. In order to elucidate some aspects of the induction mechanism of the IFN genes, we examined the effects of different treatments on IFN production in L929 cells, a well-characterized system, and in primary spleen cells. Our results indicate that 2-Aminopurine (2-AP) inhibits type I IFN (IFN-alpha and IFN-beta) induction in L929 cells but not in spleen cells. In L929 cells, 2-AP inhibited the induction of the MuIFN-beta promoter and of promoters containing tetrahexamer and PRDII sequences linked to a reporter gene. Inhibition of activation of the inducible factors binding to the MuIFN-beta promoter and sub-elements was also observed. In contrast, factors binding to the MuIFN-beta promoter are present constitutively in spleen cell nuclei and their activity is not inhibited by 2-AP. These results suggest that 2-AP inhibits IFN-beta gene induction in L929 cells through blocking of activation of the inducible DNA-binding factors which interact with the IFN-beta promoter.

2-Aminopurine↗
PubMed1991

A systemic lupus erythematosus-derived human hybridoma autoantibody reactive with antigens expressed on ADP-activated platelets.

Hematological complications seen in systemic lupus erythematosus (SLE) patients may be caused by the binding of specific autoantibodies to platelets, but the epitopes on platelets responsible for antibody binding and the mechanisms by which autoantibodies induce hemostatic abnormalities in SLE patients remain unknown. We have previously demonstrated that polyspecific platelet-binding antibodies can be derived from SLE patients. In the present study, we have characterized an SLE-derived polyspecific hybridoma antibody, 9604, which was previously shown to be strongly cytotoxic to platelets in vitro and to have weak lupus anticoagulant activity. We demonstrated that this antibody does not bind to fixed intact platelets in an enzyme-linked immunoassay (ELISA), but does react with lysed, washed or ADP-activated platelets. By Western blotting analysis, antibody 9604 was unique among other platelet-binding autoantibodies in that it reacted mainly with polypeptides of approximately 200,000 and 32,000 molecular weight (MW) in platelets. In blots of endothelial cell proteins, 9604 reacted with a band of approximately 200,000 MW, but no 32,000 MW reactive band was observed. Based on these findings, we postulate that antibody 9604 may bind to a protein or proteins of 32,000 MW exposed on the platelet surface during activation. To our knowledge, this is the first demonstration of a human hybridoma monoclonal antibody derived from an SLE patient which distinguishes between activated and resting platelets. Further characterization of the proteins recognized by this autoantibody may provide insight into the mechanisms responsible for the production and pathogenesis of anti-platelet autoantibodies in patients with SLE.

Adenosine Diphosphate↗
PubMed1991

Detection of endothelial cell-reactive immunoglobulin in patients with anti-phospholipid antibodies.

Individuals with anti-phospholipid antibodies are at increased risk for the development of thrombosis and fetal loss. The pathogenesis of these syndromes is unknown, but may involve antibody-mediated alterations in endothelial cell coagulant activity. To address this possibility, we determined the incidence of endothelial cell-reactive antibodies in 76 patients whose plasma contained anti-phospholipid antibodies, but who had no clinically-evident immune disorder. Plasma from 47 patients deposited significantly more immunoglobulin on cultured endothelial cells than control plasma. Positive tests were more frequent in patients with a history of thrombosis than in those without (17/19 v 23/48; P = 0.004). However, we observed no correlation between immunoglobulin deposition on cardiolipin and endothelial cells by individual plasmas. Furthermore, endothelial cell reactivity was not diminished by adsorption of anti-cardiolipin antibodies from patient sera using liposomes. Immunoglobulin fractions prepared from 5/6 patient sera immunoprecipitated a approximately 70 kDa endothelial cell surface protein; 4/5 of these fractions also induced the release of von Willebrand factor from endothelial cells. These results demonstrate that plasma from many patients with anti-phospholipid antibodies, but no clinically-evident autoimmune disease, also contains endothelial cell-reactive antibodies. Detection of such antibodies might help identify individuals in this patient population at greatest risk for thrombosis.

Antibodies↗
PubMed1990

Differences between human hybridoma platelet-binding antibodies derived from systemic lupus erythematosus patients and normal individuals.

The binding and functional activities of platelet-binding hybridoma autoantibodies from SLE patients were compared with those derived from normal individuals. Twenty-nine SLE-derived hybridoma antibodies and 20 normal-derived hybridoma antibodies were analyzed for binding to glutaraldehyde fixed platelets, dDNA and phospholipids, and for lupus anticoagulant activity. Twenty-four of the 29 SLE-derived antibodies and 9 of the 20 normal-derived antibodies showed one or more activities in these assays. Of the 24 SLE-derived antibodies, 8 (33.3%) were reactive in only one assay (monospecific), while the other 16 (66.7%) had more than one of these activities (polyspecific). In contrast, none (0%) of the 9 normal-derived antibodies with known activities were monospecific, while all 9 (100%) showed polyspecificity. Statistical analyses demonstrated that there was no correlation of anti-DNA activity with anti-platelet and most anti-phospholipid activities for the SLE-derived antibodies, and strong positive correlations between these reactivities for the normal-derived antibodies. Similarly, differences were observed in Western blotting analyses; SLE-derived antibodies bound more specifically to individual platelet proteins than normal-derived antibodies. Moreover, in chromium-51 release assays, all of the SLE-derived platelet-binding antibodies were cytotoxic to platelets, while none of the normal-derived platelet-binding antibodies showed significant cytotoxicity. Our results suggest that hybridoma platelet-binding autoantibodies derived from SLE patients exhibit greater antigen specificity and functional activity than similar antibodies derived from normal individuals.

Antibodies, Antinuclear↗
PubMed1987

Lupus anticoagulant and antiplatelet properties of human hybridoma autoantibodies.

The clinical association of lupus anticoagulant antibodies with thrombocytopenia and thrombosis was the rationale for investigating the in vitro reactivity of these human hybridoma lupus anticoagulant antibodies with platelets. Fifty human hybridoma antibodies from 13 patients with systemic lupus erythematosus, 2 women with multiple spontaneous abortions, and 4 normal individuals were analyzed for lupus anticoagulant, antiplatelet, anti-DNA, and antiphospholipid reactivities. Of the hybridoma antibodies studied, 25 had lupus anticoagulant activity, 21 had antiplatelet reactivity, and 7 of these antibodies had both lupus anticoagulant and antiplatelet properties. No correlation was found between lupus anticoagulant antibody activity and antiplatelet, anti-denatured DNA, anticardiolipin, anti-egg phosphatidylethanolamine, antiphosphatidylserine, antiphosphatidylinositol, and antiphosphatidylcholine reactions. In contrast, antiplatelet activity was strongly correlated with antiphosphatidylethanolamine (rho = 0.761, p less than 0.001), anticardiolipin (rho = 0.748, p less than 0.001), and anti-dDNA (rho = 0.745, p less than 0.001) reactivities. Pretreatment of platelets with deoxyribonuclease, ribonuclease, trypsin, or phospholipases A2 and C resulted in different effects on the binding of individual hybridoma antibodies to platelets, suggesting that antiplatelet antibodies may recognize different epitopes on the platelet membrane. Our data demonstrate that most hybridoma lupus anticoagulant antibodies did not bind directly to platelets in vitro. This suggests that additional serum factors may be required in vivo to explain the association of these antibodies with thrombocytopenia and thrombosis.

Antibody Specificity↗