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Biomedical subjects

D C Wong

Publications and source records attributed to D C Wong.

18 recordsLinked to original sources
PubMed1992

Lack of protective immunity against reinfection with hepatitis C virus.

Some individuals infected with hepatitis C virus (HCV) experience multiple episodes of acute hepatitis. It is unclear whether these episodes are due to reinfection with HCV or to reactivation of the original virus infection. Markers of viral replication and host immunity were studied in five chimpanzees sequentially inoculated over a period of 3 years with different HCV strains of proven infectivity. Each rechallenge of a convalescent chimpanzee with the same or a different HCV strain resulted in the reappearance of viremia, which was due to infection with the subsequent challenge virus. The evidence indicates that HCV infection does not elicit protective immunity against reinfection with homologous or heterologous strains, which raises concerns for the development of effective vaccines against HCV.

Acute Disease↗
PubMed1992

Effect of pili-specific antibodies on the adherence of Haemophilus influenzae type b to human buccal cells.

Different strains of Haemophilus influenzae type b (Hib) produce antigenically distinct pili that mediate adherence to human buccal epithelial cells. This study determined the ability of antibodies specific for the LKP3 pili of Haemophilus influenzae type b to inhibit the adherence of Hib strain Eagan (p+). Antiserum was prepared by immunization of rabbits with pili purified from Hib strain Eagan (p+). The presence of pili-specific antibodies in the immune serum was shown by selective immunoprecipitation of pilin and by electron microscopy of cells labeled with immunogold. Immune serum, affinity-purified antibody, and Fab fragments from immune serum significantly inhibited (P less than .001) adherence of strain Eagan (p+) to human buccal epithelial cells whereas preincubation with preimmune rabbit serum or Fab fragments from preimmune serum had no significant effect on adherence. Dilution of the immune serum, affinity-purified antibodies, or Fab fragments from immune serum resulted in decreased inhibition of Hib adherence. These results indicate that antibodies specific for LKP3 pili can effectively inhibit adherence of Hib strain Eagan (p+) and probably other strains that express this pilus serotype.

Agglutination Tests↗
PubMed1992

The natural history of infection with hepatitis C virus (HCV) in chimpanzees: comparison of serologic responses measured with first- and second-generation assays and relationship to HCV viremia.

The sensitivity of first- and second-generation tests for antibody to hepatitis C virus (HCV) and the relationship among the patterns of antibody response and HCV viremia were examined in serial serum samples from 6 chimpanzees experimentally infected with HCV and followed less than or equal to 3 years. HCV infection was transient in 4 chimpanzees and became chronic in 2. All chimpanzees developed antibodies to HCV detectable by second-generation assays, while only 5 of the 6 became positive by first-generation assay. Second-generation were consistently more sensitive than first-generation assays for the early diagnosis of primary HCV infection. The pattern observed with second-generation assays was not influenced by the outcome of HCV infection, since antibodies remained persistently detectable throughout follow-up regardless of whether viremia was transient or persistent. In contrast, the first-generation antibody response was variable: It usually disappeared after loss of viremia, whereas its presence paralleled HCV viremia in chimpanzees with chronic infection.

Animals↗
PubMed1990

Early events in hepatitis C virus infection of chimpanzees.

The cytoplasmic antigen and ultrastructural changes we described previously for chimpanzees (Pan troglodytes) infected with hepatitis C virus (HCV) or with hepatitis D virus have recently been shown to be indirect measures of viral replication and appear to represent a host response to the expression or action of interferon. The time of appearance of these changes in hepatocytes during HCV infection, when compared with similar changes in hepatitis D virus infection, suggests a very early replicative phase for HCV. To investigate the early events in HCV infection, we infected two chimpanzees with HCV and obtained blood and liver biopsy samples from them daily during the first 10 days of infection. The early stage of infection with regard to HCV replication, antigen expression, and ultrastructural changes was similar in both chimpanzees. When tested by cDNA/polymerase chain reaction, HCV sequences became detectable in the serum as early as 3 days after inoculation and remained positive through the peak of aminotransferase elevations. In one chimpanzee the peak of virus production appeared to be 7 weeks after inoculation, which was coincident with rising enzyme values. The cytoplasmic antigen, detected by immunofluorescence, and ultrastructural changes, detected by electron microscopy, became positive in hepatocytes 3 and 6 days, respectively, after HCV sequences were first detected in serum. Circulating anti-HCV appeared 13 weeks and 32 weeks after inoculation, respectively, in the chimpanzees. These data indicate a very early replicative phase for HCV and a potentially long period of infectivity before the appearance of anti-HCV.

Animals↗
PubMed1989

Selection of amidases with novel substrate specificities from penicillin amidase of Escherichia coli.

To obtain amidases with novel substrate specificity, the cloned gene for penicillin amidase of Escherichia coli ATCC 11105 was mutagenized and mutants were selected for the ability to hydrolyze glutaryl-(L)-leucine and provide leucine to Leu- host cells. Cells with the wild-type enzyme did not grow in minimal medium containing glutaryl-(L)-leucine as a sole source of leucine. The growth rates of Leu- cells that expressed these mutant amidases increased as the glutaryl-(L)-leucine concentration increased or as the medium pH decreased. Growth of the mutant strains was restricted by modulation of medium pH and glutaryl-(L)-leucine concentration, and successive generations of mutants that more efficiently hydrolyzed glutaryl-(L)-leucine were isolated. The kinetics of glutaryl-(L)-leucine hydrolysis by purified amidases from two mutants and the respective parental strains were determined. Glutaryl-(L)-leucine hydrolysis by the purified mutant amidases occurred most rapidly between pH 5 and 6, whereas hydrolysis by wild-type penicillin amidase at this pH was negligible. The second-order rate constants for glutaryl-(L)-leucine hydrolysis by two "second-generation" mutant amidases, 48 and 77 M-1 s-1, were higher than the rates of hydrolysis by the respective parental amidases. The increased rates of glutaryl-(L)-leucine hydrolysis resulted from both increases in the molecular rate constants and decreases in apparent Km values. The results show that it is possible to deliberately modify the substrate specificity of penicillin amidase and successively select mutants with amidases that are progressively more efficient at hydrolyzing glutaryl-(L)-leucine.

Amidohydrolases↗
PubMed1989

Alteration of the catalytic efficiency of penicillin amidase from Escherichia coli.

Ampicillin and cephalexin are beta-lactam antibiotics that are synthesized by the condensation of D-(-)-alpha-aminophenylacetic acid with 6-aminopenicillanic acid or 7-aminodeacetoxycephalosporanic acid, respectively. The rates at which the penicillin amidase of Escherichia coli catalyzes these reactions are too low to be of practical use. The objective of this study was to determine whether it is possible to alter the substrate specificity of penicillin amidase and select enzymes that efficiently hydrolyze substrates with alpha-aminophenylacetyl moieties at low pH, at which the alpha-amino group is nearly completely protonated. In this study, D-(-)-alpha-aminophenylacetyl-(L)-leucine (APAL) was used as a substrate analog of ampicillin and cephalexin. The gene for the penicillin amidase of E. coli ATCC 11105 was cloned and transferred to a leucine auxotroph of E. coli; numerous amidase mutants were selected by their ability to cleave APAL and provide leucine for growth in low-pH medium. The plasmid encoding one of the mutant amidases (pA135) was used to transform naive cells, and transformants that expressed the mutant amidase were shown to grow more rapidly in medium at pH 6.5 containing 0.1 mM APAL as the sole leucine source than did cells with the wild-type amidase. The mutant amidase was purified, and the second-order rate constant (kcat/Km) for APAL hydrolysis at pH 6.5 was found to be 10-fold greater than the rate observed with the wild-type enzyme. The difference between the rates of APAL hydrolysis by the mutant and wild-type amidases increased as the pH of the reactions decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Amidohydrolases↗
PubMed1979

Prevalence of antibody to hepatitis A and hepatitis B viruses in selected populations of the South Pacific.

Five island populations representing the three major cultural groups of the South Pacific--Polynesia, Micronesia, Melanesia--were studied for prevalence of antibody to hepatitis A virus (anti-HAV) and of antibody to the core antigen of hepatitis B virus (anti-HBc). Sera were collected in the late 1950s and early 1960s, selected where possible for appropriate age and sex distributions, and were tested by radioimmunoassay. Rather marked differences in prevalence were observed. Anti-HBc patterns confirmed that HBV is endemic in the Pacific populations. Furthermore, the patterns differed somewhat from each other and did not correlate with ethnogeographic area. Prevalence of anti-HAV was high in all populations studied. A Unique pattern was found for the island of Ponape (Micronesia): In a Ponape population bled in 1963, anti-HAV was not detected in any individual under 20 years of age, but almost all individuals over that age were found to be seropositive. On testing a second group of sera collected in 1975, all individuals aged 14--21 years were found to be antibody positive, indicating that HAV had returned to Ponape sometime prior to 1975. There was no significant difference in the prevalence of HAV or HBV infection between males and females in any of the populations studied.

Adolescent↗
PubMed1978

Enzyme-linked immunosorbent assay for detection of hepatitis A antigen in stool and antibody to hepatitis A antigen in sera: comparison with solid-phase radioimmunoassay, immune electron microscopy, and immune adherence hemagglutination assay.

Previously described techniques for detection of hepatitis A antigen (HA Ag) and antibody (anti-HA) have required purified HA Ag and expensive equipment. Herein is described an enzyme-linked immunosorbent assay (ELISA) for specific detection of HA Ag in human stool filtrates and of anti-HA in sera by using selected HA Ag-containing human stool filtrates as the antigen source. Because human stools often react nonspecifically in serological tests for HA Ag, blocking with preexposure and hyperimmune anti-HA sera from a chimpanzee inoculated with hepatitis A virus was used to confirm specific detection of HA Ag. The sensitivity of ELISA was found to be comparable to that of solid-phase radioimmunoassay (SPRIA) and immune electron microscopy (IEM). Of 37 acute-phase stools collected from nine patients, 16 were positive for HA Ag by ELISA. In 13 of these, HA Ag particles were found by IEM, and an additional 3 stools negative by ELISA contained HA Ag particles by IEM. Eight control stools were negative by both ELISA and IEM. Anti-HA was measured in sera by demonstrating its ability to block binding of the enzyme conjugate to HA Ag in a stool without detectable nonspecificity. This test (blocking ELISA) was as sensitive and specific as blocking SPIRA, IEM, and immune adherence hemagglutination and, like SPRIA and IEM, detected early-developing antibody. The ELISA is simple to perform and requires only a minimum of equipment. It is useful for screening stools for HA Ag and for monitoring HA Ag during purification, as well as for detecting early and late anti-HA in sera.

Acute Disease↗
PubMed1977

Non-A, non-B post-transfusion hepatitis.

To clarify the role of hepatitis-A virus (H.A.V.) in the aetiology of post-transfusion hepatitis unrelated to hepatitis-B virus, we have tested and titred pre-transfusion and convalescent serum samples from 32 patients for antibody to hepatitis-A antigen (anti-HA) by quantitative immune adherence haemagglutination. 12 patients had no detectable anti-HA in either pre-transfusion or late convalescent serum; the other 20 had anti-HA in pretransfusion serum and no significant chance in titre during convalescence. This study excludes H.A.V. as the agent responsible for these cases of post-transfusion hepatitis and supports the existence of "non-A, non-B" hepatitis virus(es).

Antibodies, Viral↗
PubMed1976

Modification of chronic hepatitis-B virus infection in chimpanzees by administration of an interferon inducer.

Chimpanzees chronically infected with hepatitis-B virus showed transient changes in several markers of infection when treated with the interferon inducer polyriboinosinic-polyribocytidylic acid-poly-l-lysine carboxymethyl cellulose. Serum Dane-particle-associated D.N.A. polymerase, e antigen and hepatitis-B surface antigen, and intrahepatic hepatitis-B surface and core antigens diminished during treatment. Defective (D.N.A.-polymerase-negative) Dane particles increased in titre transiently during treatment; these may play a role in the modulation of hepatitis-B virus infection. Humoral immune responses in chronic hepatitis-B carrier chimps were unaffected. Interferon inducers (or exogenous interferon) may be useful for the treatment of chronic hepatitis-B virus infection.

Animals↗
PubMed1976

Distribution of antibody to hepatitis a antigen in urban adult populations.

To investigate the prevalence and distribution of antibody to hepatitis A antigen we tested 947 randomly selected people in the Greater New York City area; 45 per cent were antigen positive, as determined by the immune adherence method. Antibody was detected two to three times more frequently in lower social classes (72 to 80 per cent) than in middle and upper-middle classes (18 to 30 per cent). The rate of antibody detection was strongly correlated with age; the prevalence gradually increased throughout adulthood and reached its peak level in people 50 years of age and older. Those with serologic evidence of past exposure to hepatitis B virus were significantly more often antibody positive than those without such evidence (61 vs. 40 per cent; P less than 0.001). Very few of the positive subjects had had hepatitis. The prevalence of this antibody varies among different population groups, increases with age, decreases with rise in socioeconomic status, is independent on sex and race, and correlates with serologic evidence of hepatitis B virus infections.

Adolescent↗
PubMed1976

Mussel-associated viral hepatitis, type A: serological confirmation.

7 members of a family of 14 developed acute viral hepatitis approximately one month after a family outing. Epidemiological investigation incriminated incompletely cooked mussels (Mytilus edulis) as the vehicle of infection and revealed a statistically significant difference in attack-rates between mussel-ingesters (70%) and non-ingesters (0%) (P=0-035). The aetiological role of hepatitis-A virus, suspected on epidemiological grounds, was serologically confirmed by the demonstration of rises in titres of serum-antibody to hepatitis-A antigen (serologically related to the MS-1 strain of hepatitis-A virus), determined by immune adherence haemagglutination.

Acute Disease↗
PubMed1976

Purification of hepatitis A antigen from feces and detection of antigen and antibody by immune adherence hemagglutination.

Hepatitis A antigen (HA Ag) was purified from feces collected during acute illness from patients with naturally occurring viral hepatitis, type A. Positive fecal specimens were identified by immune electron microscopy, but for detection of HA Agduring purification immune adherence hemagglutination (IAHA) and microtiter solid-phase radioimmunoassay were used. Isopycnic banding in cesium chloride, rate-zonal separation in sucrose, and preparative zonal electrophoresis were used in various combinations for successive purification, and the purified antigen was successfully used in a test for antibody by IAHA. Seronconversions to HA Ag were demonstrated by IAHA in 20 instances of hepatitis A virus infection, but in none of six cases of type B hepatitis or three cases of post-transfusion hepatitis unrelated to heaptitis A or B viruses, nor in two individuals without hepatitis. In addition, the temporal pattern of antibody development during type A hepatitis was studied in serial sera from an experimentally infected chimpanzee. Antibody titers by IAHA correlated well with antibody ratings determined by immune electron microscopy.

Antibodies, Viral↗
PubMed1976

Comparison of serological tests for antibody to hepatitis A antigen, using coded specimens from individuals infected with the MS-1 strain of hepatitis A virus.

To compare serological tests for antibody to hepatitis A antigen (anti-HA), we tested 15 paired serum specimens, submitted under code, from individuals infected with the MS-1 strain of hepatitis A virus. Immune electron microscopy (IEM), immune adherence hemagglutination (IAHA), and solid-phase radioimmunoassay (RIA) tests for anti-HA were performed with hepatitis A antigen (HA Ag) derived from human stool; results were also compared with previously reported titers determined by IAHA with HA Ag derived from marmoset liver. Antibody titers (IAHA and RIA) and ratings (IEM) determined with stool-derived HA Ag compared favorably, and a seroresponse to HA Ag was detected by all three methods for every serum pair tested. Differences in titers were noted between IAHA tests with liver-derived and with stool-derived HA Ag, but the discrepancies could be accounted for by differences in test technique. The agreement found in this study among the three techniques was quite good and confirms the specificity and sensitivity of tests for anti-HA that are done with stool-derived HA-Ag.

Antibodies, Viral↗
PubMed1976

A microtiter solid-phase radioimmunoassay for hepatitis A antigen and antibody.

A microtiter solid phase radioimmunoassy for hepatitis A antigen (HA Ag) and antibody (anti-HA) was developed. The test was more sensitive than immune adherence hemagglutination for detecting HA Ag and almost as sensitive for detecting anti-HA. The specificity and sensitivity of reagents were examined and optimum conditions for the test were determined. Radioimmunoassay, immune adherence hemagglutination, and immune electron microscopy were compared for detecting anti-HA. A serologic response to HA Ag was detected in paired sera from patients with type A hepatitis but not from patients with type B or non-A, non-B hepatitis by all three techniques.

Animals↗
PubMedDate not supplied

Serologic and animal inoculation studies of a communal outbreak of viral hepatitis, type A.

Sera from individuals in an outbreak of viral hepatitis in a multifamily household, probably spread by contaminated food, were studied for antibodies to hepatitis A virus (anti-HAV), and selected acute phase sera were inoculated into marmosets. Significant rises in anti-HAV titers between acute and convalescent sera occurred in all of 15 individuals in the outbreak who experienced serum enzyme elevations and in one of 14 individuals whose serum enzyme levels remained normal. The remaining 13 individuals in the latter group had antibody levels in both early and late sera compatible with residual immunity from prior HAV infections and correlating with resistance to reinfection. Groups of marmosets were infected with acute phase sera from two of the cases; in both instances the inoculated sera contained substantial levels of anti-HAV. The marmosets developed specific anti-HAV seroconversions as well as enzyme elevations.

Alanine Transaminase↗