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C T Chu

Publications and source records attributed to C T Chu.

At least 37 records · Page 2Linked to original sources
PubMed1996

Human cytomegalovirus as a potential etiologic agent in recurrent aphthous ulcers and Behçet's disease.

In a preliminary study on anti-human cytomegalovirus (HCMV) antibody (Ab) by ELISA, the serum anti-HCMV/IgG Ab concentrations in 22 patients with recurrent aphthous ulcers (RAU) in the remission stage were found to be significantly higher than in 22 control subjects (121 +/- 42 vs 100 +/- 27, P < 0.05) and in 39 patients with RAU in the active stage (121 +/- 42 vs 88 +/- 45, P < 0.01). Therefore, the potential of HCMV as an etiologic agent in RAU was proposed and studies using the polymerase chain reaction (PCR) and in situ hybridization (ISH) have been performed to investigate the possible presence of HCMV DNA in pre-ulcerative oral aphthous lesions in patients with RAU or Behçet's disease (BD) of the mucocutaneous type. For this purpose, formalin-fixed biopsy specimens were obtained from 13 pre-ulcerative oral aphthous lesions, 2 samples of normal oral mucosa and 1 ileal mucosal lesion from 9 RAU patients and 4 BD patients. Five specimens of normal oral mucosa from 5 normal control subjects and 12 specimens of oral erosive or ulcerative lesions from 12 patients with erosive lichen planus (ELP) were also included. By PCR, HCMV DNA was detected in 5 of the 13 (38.5%) pre-ulcerative oral aphthous lesions, 3 from RAU patients and 2 from BD patients. The ileal mucosa specimen was also HCMV DNA-positive, whereas HCMV DNA was not demonstrated in any of the 7 specimens of normal oral mucosa from RAU patients and normal control subjects; 12 specimens of oral lesions from ELP patients were similarly negative. ISH did not detect HCMV DNA in any of the biopsy specimens from RAU patients and control subjects. Our findings suggest that HCMV may be an etiologic agent in some cases of RAU and BD.

Adolescent↗
PubMed1995

Activated alpha 2-macroglobulin promotes mitogenesis in rat vascular smooth muscle cells by a mechanism that is independent of growth-factor-carrier activity.

Vascular smooth muscle cell (vSMC) proliferation is important in atherosclerosis. We previously demonstrated that methylamine-activated alpha 2-macroglobulin (alpha 2M) and transforming growth factor beta 1 (TGF-beta 1) cause a synergistic proliferative response in quiescent rat aortic vSMCs [Stouffer, G. A., La-Marre, J., Gonias, S. L. & Owens, G. K. (1993) J. Biol. Chem. 268, 18,340-18,344]. The first goal of this study was to determine whether the synergy is due to the ability of alpha 2M-methylamine (alpha 2M-MeNH2) to bind TGF-beta 1 and target the growth factor to vSMCs that express the alpha 2M receptor. Receptor-recognized alpha 2M derivatives without TGF-beta 1-binding activity, including ternary alpha 2M-trypsin, an 18-kDa proteolytic fragment of the alpha 2M subunit, and the corresponding recombinant receptor-binding fragment (rRBF) increased vSMC [3H]thymidine incorporation and cell number in a manner similar to alpha 2M-MeNH2. In combination with TGF-beta 1, each alpha 2M derivative caused a synergistic vSMC proliferative response. vSMCs responded comparably when treated with alpha 2M-MeNH2 and TGF-beta 1 simultaneously or in sequence. Furthermore, alpha 2M-MeNH2-TGF-beta 1 complexes increased [3H]thymidine incorporation no more than alpha 2M-MeNH2 alone. These results indicate that TGF-beta 1 binding to alpha 2M is not responsible for the synergistic mitogenic activity. Additional studies were undertaken to determine whether activated alpha 2M independently induces a signal-transduction response in vSMCs. alpha 2M-MeNH2 and rRBF caused a rapid, transient increase in vSMC inositol 1,4,5-trisphosphate. This response was pertussis-toxin insensitive. Receptor-associated protein (RAP; 170 nmol/L) inhibited 91-95% of the specific binding of 125I-alpha 2M-MeNH2 and 125I-rRBF to vSMC; however, RAP did not affect the inositol 1,4,5-trisphosphate response or the mitogenic response. These studies suggest that vSMCs express a receptor, other than low-density-lipoprotein-receptor-related protein, that transduces a signal in response to activated alpha 2M. This receptor may mediate the mitogenic activity of alpha 2M in vSMC culture.

Animals↗
PubMed1995

The effect of residue 1106 on the thioester-mediated covalent binding reaction of human complement protein C4 and the monomeric rat alpha-macroglobulin alpha 1 I3.

The histidine at position 1106 of the C4B isotype of human complement is involved in catalyzing the covalent binding of the thioester to glycerol and water. By replacing the histidine with other residues, it was found that tyrosine is also capable of mediating the reaction. We propose that they act as nucleophiles by first attacking the thioester, upon activation, to form acyl intermediates, which subsequently react with the hydroxyl groups of glycerol or water. The monomeric alpha-macroglobulin, alpha 1I3 of the rat, was also studied. Unlike alpha 2-macroglobulin, which is a tetramer, alpha 1I3 has binding properties similar to those of C4A.

Amino Acid Sequence↗
PubMed1995

NKG2-C is a receptor on human natural killer cells that recognizes structures on K562 target cells.

NKG2-C is a member of the recently discovered NKG2 family of genes and proteins, which are preferentially expressed on human natural killer (NK) cells. These potential NK cell receptors belong to a larger class of type II transmembrane proteins with a C-type lectin domain. We show here that NKG2-C is expressed as a 36-kDa glycoprotein by translation in vitro, recombinant expression and immunoprecipitation from a human NK cell clone. Further, a recombinant soluble NKG2-C-receptor binds specifically to K562 cells, which are target cells for NK cell killing, and to RPMI 8866 cells, which are feeder cells for NK cells; several other hematopoietic cell lines tested do not show any binding. The binding structures on the surface of K562 cells disappear, concomitant with a loss in susceptibility to killing when the cells are induced to differentiate with phorbol ester and Ca2+ ionophore. Our data suggest the presence of specific target molecules for NKG2-C on K562 cells, since overall glycosylation, Lewis X and Lewis Y structures, as well as the mucin-like CD43 molecule, do not change following induction of the cells. We propose that NKG2-C mediates a specific interaction of NK cells and their target cells with functional importance for NK cell killing.

Animals↗
PubMed1994

The relationship between low density lipoprotein-related protein/alpha 2-macroglobulin (alpha 2M) receptors and the newly described alpha 2M signaling receptor.

alpha 2-Macroglobulin (alpha 2M)-methylamine binding to macrophages appears to involve two receptors. Binding of alpha 2M-methylamine to low density lipoprotein-related protein (LRP) results in cellular uptake and degradation, while binding to a newly described alpha 2M signaling receptor elevates intracellular calcium ([Ca2+]i) and inositol phosphates. We now demonstrate that binding of lactoferrin, Pseudomonas exotoxin A, and lipoprotein lipase to LRP on macrophages results in increased [Ca2+]i and inositol 1,4,5-triphosphate. Receptor-associated protein, which binds to LRP but not the alpha 2M signaling receptor, blocks the lactoferrin signal but has no effect on alpha 2M-methylamine signaling. The latter observation supports our hypothesis that a distinct signaling receptor binds alpha 2M-methylamine. We further demonstrate that the signaling events induced by lactoferrin may involve a pertussis toxin-sensitive G protein, while the alpha 2M signaling receptor appears to be coupled to a pertussis toxin-insensitive G protein.

Animals↗
PubMed1994

Evidence for a second alpha 2-macroglobulin receptor.

alpha 2-Macroglobulin (alpha 2M)-methylamine binds to purified low density lipoprotein receptor-related protein (LRP), and it is assumed that LRP functions as the alpha 2M receptor in vivo. Binding of alpha 2M-methylamine to macrophage receptors elevates intracellular calcium ([Ca2+]i), inositol phosphates, and cyclic AMP. We have employed human alpha 2M-methylamine and recombinant receptor binding fragment (RBF) to study transduction mechanisms. Macrophages exposed to either ligand demonstrated a rapid rise in [Ca2+]i. Since the 39-kDa LRP/alpha 2M receptor-associated protein (RAP) blocks alpha 2M binding to LRP, we explored the effects of RAP upon signaling. Pretreatment of macrophages with RAP did not block the increase in [Ca2+]i elicited by alpha 2M-methylamine or RBF, suggesting a distinct binding site. RBF also elicited a transient 1.5-2.0-fold increase in inositol 1,4,5-triphosphate. In permeabilized macrophages, GTP gamma S and Gp-p(NH)p potentiated and sustained this inositol 1,4,5-triphosphate increase. Preincubation of permeabilized macrophages with GDP beta S abrogated the effects of GTP gamma S. Our results suggest that the signaling alpha 2M receptor is coupled to a pertussis toxin-insensitive G protein and possibly to a cholera toxin-sensitive G protein. We conclude that macrophages contain a second alpha 2M receptor that is G protein-coupled.

Adenosine Diphosphate Ribose↗
PubMed1994

Adjuvant-free in vivo targeting. Antigen delivery by alpha 2-macroglobulin enhances antibody formation.

The proteinase "inhibitor" alpha 2-macroglobulin (alpha 2M) is able to entrap and form covalent linkages with diverse proteins during a transient proteinase-activated state. These complexes are rapidly endocytosed after binding to receptors present on macrophages and other cells. We have previously shown that compared to free hen egg lysozyme (HEL), alpha 2M-complexed HEL undergoes enhanced macrophage uptake, processing, and presentation to T hybridoma clones in vitro. Inasmuch as it is not clear whether T hybridoma responses accurately reflect primary immune responses in vivo, we studied antibody production in rabbits using two Ag complexed with either human alpha 2M (H alpha 2M) or a homologous protein purified from rabbit plasma, alpha 1-macroglobulin (R alpha 1M). Pathogen-free NZW rabbits received s.c. injections with adjuvant-free preparations of free HEL or porcine pancreatic elastase (PPE), H alpha 2M-HEL-PPE complexes, R alpha 1M-HEL-PPE complexes, or mixtures of the uncomplexed proteins. Complexing the Ag to alpha 2M resulted in 10 to 500-fold higher IgG titers compared to uncomplexed controls. Injection of Ag complexed to either H alpha 2M or R alpha 1M resulted in levels of anti-HEL IgG comparable to those elicited by emulsification in CFA. Inasmuch as inflammatory proteinases such as neutrophil elastase can initiate covalent complex formation with alpha 2M, we propose that "proteinase-activated" alpha 2M may mediate receptor-enhanced Ag uptake by macrophages, resulting in augmented Ag processing and antibody production.

Animals↗
PubMed1993

Receptor-recognized alpha 2-macroglobulin-methylamine elevates intracellular calcium, inositol phosphates and cyclic AMP in murine peritoneal macrophages.

Human plasma alpha 2-macroglobulin (alpha 2M) is a tetrameric proteinase inhibitor, which undergoes a conformational change upon reaction with either a proteinase or methylamine. As a result, a receptor recognition site is exposed on each subunit of the molecule enabling it to bind to its receptors on macrophages. We have used Fura-2-loaded murine peritoneal macrophages and digital video fluorescence microscopy to examine the effects of receptor binding on second messenger levels. alpha 2M-methylamine caused a rapid 2-4-fold increase in intracellular Ca2+ concentration ([Ca2+]i) within 5 s of binding to receptors. The agonists induced a focal increase in [Ca2+]i that spread out to other areas of the cell. The increase in [Ca2+]i was dependent on the alpha 2M-methylamine concentration and on the extracellular [Ca2+]. Both sinusoidal and transitory oscillations were observed, which varied from cell to cell. Neither alpha 2M nor boiled alpha 2M-methylamine, forms that are not recognized by the receptor, affected [Ca2+]i in peritoneal macrophages under identical conditions of incubation. The alpha 2M-methylamine-induced rise in [Ca2+]i was accompanied by a rapid and transient increase in macrophage inositol phosphates, including inositol tris- and tetrakis-phosphates. Native alpha 2M did not stimulate a rise in inositol phosphates. Finally, binding of alpha 2M-methylamine to macrophages increased cyclic AMP transiently. Thus receptor-recognized alpha-macroglobulins behave as agonists whose receptor binding causes stimulation of signal transduction pathways.

Animals↗
PubMed1993

Receptor-mediated antigen delivery into macrophages. Complexing antigen to alpha 2-macroglobulin enhances presentation to T cells.

Macrophages secrete alpha 2-macroglobulin (alpha 2M), a protein that may facilitate early Ag handling. alpha 2M is able to entrap and form covalent linkages with diverse proteins during a transient proteinase-activated state. The resulting complexes are rapidly endocytosed after binding to high affinity receptors. Such a system could be capable of efficiently delivering a multitude of proteins to macrophages. We have used T hybridoma clones that respond only to hen egg lysozyme, in a MHC-restricted manner, to probe the effect of complex formation on Ag uptake and processing by murine macrophages. Radiolabeled lysozyme was internalized more rapidly and to a greater extent when bound to alpha 2M than when unbound. Macrophages pulsed with lysozyme-alpha 2M-elastase complexes required 200 to 250 times less Ag than those pulsed with free lysozyme to achieve effective presentation to T cells. Adding equimolar amounts of alpha 2M-elastase complexes, or of alpha 2M-methylamine, to free lysozyme had no effect on basal lysozyme presentation. Receptor-recognized forms of alpha 2M, but not lysozyme or BSA, competed effectively for both uptake and presentation of lysozyme-alpha 2M-elastase complexes. These results indicate that proteinase-activated alpha 2M can enhance Ag processing by carrying Ag into macrophages through a receptor-mediated process.

Animals↗
PubMed1993

HLA-DR and DQ antigens in Chinese patients with Behçet's disease.

The frequencies of HLA-DR and DQ antigens in 24 Chinese patients with Behçet's disease (BD) were calculated and compared with those in 130 healthy control Chinese and those in 80 Chinese patients with recurrent oral ulcers (ROU). Although an increased trend of DRw6 and DRw8 antigens in patients with BD was noted, there was no significant difference in frequencies of HLA-DR and DQ antigens between patients with BD and healthy control subjects or patients with ROU after correction of P values (Pc > 0.05). Further analysis of our data of the phenotype frequencies of DRw6 and DRw8 antigens according to the subtypes of BD also showed the increased frequencies of DRw6 and DRw8 antigens in patients with mucocutaneous type of BD as compared with those in healthy control subjects. However, only the phenotype frequency of DRw8 antigen in patients with mucocutaneous type of BD was significantly higher than that in patients with ROU (P < 0.005, Pc < 0.05, relative risk = 17.7, and etiologic fraction = 0.30). This significant increase of the phenotype frequency suggests that the gene coding for HLA-DRw8 antigen in patients with ROU was only partially (30%) responsible for susceptibility to the mucocutaneous type of BD.

Adolescent↗
PubMed1991

Mechanism of insulin incorporation into alpha 2-macroglobulin: implications for the study of peptide and growth factor binding.

In recent years, many studies have suggested a direct role for alpha 2-macroglobulin (alpha 2M), a plasma proteinase inhibitor, in growth factor regulation. When coincubated in the presence of either trypsin, pancreatic elastase, human neutrophil elastase, or plasmin, 125I-insulin rapidly formed a complex with alpha 2M which was greater than 80% covalent. The covalent binding was stable to reduction but abolished by competition with beta-aminopropionitrile. Neither native alpha 2M nor alpha 2M pretreated with proteinase or methylamine incorporated 125I-insulin. Experiments utilizing alpha 2M cross-linked with cis-dichlorodiammineplatinum(II) indicated that 125I-insulin must be present during alpha 2M conformational change to covalently bind. A maximum stoichiometry of 4 mol of insulin bound per mole of alpha 2M and the short half-life of the alpha 2M intermediate capable of covalent incorporation were consistent with thiol ester involvement. Protein sequence analysis of unlabeled insulin-alpha 2M complexes, together with results of beta-aminopropionitrile competition, confirmed that insulin incorporation occurs via the same gamma-glutamyl amide linkage responsible for covalent proteinase and methylamine binding to alpha 2M. Although intact insulin apparently incorporated through its sole lysine residue on the B chain, we found that isolated A chain also bound covalently to alpha 2M. Phenyl isothiocyanate derivatization of the N-terminus had no effect on A-chain binding, supporting the possibility of heretofore unreported gamma-glutamyl ester linkages to alpha 2M.

Binding Sites↗
PubMed1991

Mechanisms of depressed natural killer cell activity in recurrent aphthous ulcers.

Natural killer (NK) cell activity was studied serially in the peripheral blood obtained from 35 patients with recurrent aphthous ulcers (RAU) and from 46 age/sex-matched normal healthy controls. The NK cell activity was assayed by a 4-hr 51Cr release assay using K562 cells as targets. The results showed that the patients in remission (2 weeks of convalesence) had normal NK cell activity compared to that of normal controls. Four stages of evolution (early, exacerbation, postexacerbation, and convalescence) in these patients were further evaluated. Increased NK cell activity in the exacerbation of major aphthous ulcer was noted. In contrast, depressed NK cell activity in postexacerbation and in 1 week of convalescence was found at different effector/target (E/T) ratios. The depressed NK cell activity was interpreted as temporary and a secondary phenomenon in the immunopathogenesis of this disease. Partial restoration of depressed NK cell activity by adding recombinant interleukin-2 (rIL-2) suggests that other factors are also involved in the process or that IL-2 deficiency exists in RAU patients. However, no deficiency of plasma IL-2 and interferon-gamma (IFN-gamma) was noted. The percentage of large granular lymphocytes (LGL, NK/K) was correlated with NK cell activity, with both parameters being depressed in the postexacerbation of RAU patients. NK cell activity of RAU patients was still depressed after the depletion of plastic adherent cells. Suprisingly, in contrast to the remission stage, unresponsiveness to rIL-2 of normal NK cell activity in the exacerbation stage was found. The discrepancy was not associated with different subpopulations of NK heterogeneous cells. Immunopathogenesis of RAU on the NK-IFN-IL-2-IL-2R system needs further clarification.

Adolescent↗
PubMed1991

Strong association of HLA-DRw9 in Chinese patients with recurrent oral ulcers.

The frequency of HLA-DR and -DQ antigen occurrence was investigated in 80 Chinese patients with recurrent oral ulcers and 107 matched healthy control subjects of the same ethnic group. No significant differences in the presence of HLA-DQ antigens were found. However, the HLA-DRw9 antigen occurs more frequently in patients with recurrent oral ulcers (p less than 0.0001, corrected p less than 0.005) and may be considered as a genetic marker of the disease in the Chinese population.

Adult↗
PubMed1991

Lysis of herpes simplex virus-infected cells by lymphokine-activated killer cells.

Activation of human peripheral blood mononuclear cells (PBMC) or murine splenocytes with recombinant interleukin-2 (rIL-2) has been found to be able to generate cells which are lytic in vitro for a variety of cells infected by herpes simplex virus (HSV). Lymphokine-activated killer (LAK) cells were generated by the incubation of human PBMC or murine splenocytes with 500 u/ml of rIL-2 for 3 to 4 days in a CO2 incubator at 37 degrees C. These cells were lytic to cultured tumor cell lines, yet sparing normal primary cell cultures as has been reported. Human PBMC infected with HSV, however, were susceptible to the lytic effect of these LAK cells. From 30 to 50 percent lysis of HSV-infected human PBMC was observed when the effector-to-target ratios were 40:1 and 100:1 respectively by four hr 51Cr-release assays. Similar cytolytic effect was observed when mouse embryonic fibroblasts (MEF) were infected with HSV and used as targets when rIL-2-activated mouse splenocytes were used as effectors. The cytolytic effects of LAK cells on the HSV-infected cells can be demonstrated even after lowering of NK activities by the treatment of effector cells with anti-NK antibody Leu-11b plus complement. Cytolytic effects were not restricted to the autologous system, and could be demonstrated in the heterologous system as well. Human LAK cells killed not only HSV-infected autologous PBMC but also infected mouse embryonic fibroblasts. However, mouse LAK cells exhibit species-specific cytotoxicity. In conclusion, it was demonstrated that LAK cells are cytolytic to HSV-infected cells in both human and murine systems.

Animals↗
PubMed1991

Effect of fetal sex on maternal and fetal human chorionic gonadotropin levels and comparison of their levels in paired umbilical arteries and veins.

There were discordant results regarding the effect of fetal sex on human chorionic gonadotropin (hCG) concentrations in maternal or fetal circulation and regarding whether the levels in umbilical arteries are equal to those in umbilical veins. Totally, 188 singleton pregnancies at 36 to 42 weeks of gestation without any obstetrical or medical complication were studied. The hCG levels were measured by radioimmunoassay specific for hCG using Sb3 antibody raised against beta-subunit of hCG. The maternal ages and parities between those who gave birth to a male or a female baby were not different statistically. The birth weights between male and female babies were also not different. The serum hCG levels had a wide range in maternal circulation (200-75,200 mIU/ml) and their distribution was positively skewed. The mean value (geometric mean, G.M.) in maternal circulation for those who carried a female fetus (11,500 mIU/ml) was significantly higher than that for those carrying a male fetus (6,470 mIU/ml) (P less than 0.001, Student's t-test). The hCG concentrations in umbilical veins of female fetuses were also higher than in those of male fetuses (G.M., 26.8 vs 19.5 mIU/ml, P less than 0.01, Student's t-test). Umbilical arterial hCG levels (G.M., 10.05 mIU/ml) were statistically not different from umbilical venous levels (G.M., 10.92 mIU/ml) (paired t-test).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗