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Biomedical subjects

N J Schmidt

Publications and source records attributed to N J Schmidt.

At least 109 records · Page 6Linked to original sources
PubMed1971

Relative sensitivity of gel diffusion, complement fixation, and immunoelectroosmophoresis tests for detection of hepatitis-associated antigen and antibody.

The immunoelectroosmophoresis (IEOP) test was compared with gel diffusion and complement fixation (CF) tests for sensitivity in detecting hepatitis-associated antigen (HAA) in the sera of hepatitis patients, for titration of HAA, and for detection of antibody to HAA. The IEOP test was found to be slightly more sensitive than either gel diffusion or CF tests for detection of antigen in the patients' sera. Titers of HAA demonstrated by IEOP were higher than those seen in gel diffusion tests but lower than CF titers. The gel diffusion test with an "enhancement" pattern was found to be more reliable than the other two procedures for detection of low levels of anti-HAA, due to the greater inhibitory effect of an antigen excess in the IEOP system and the possible masking of low levels of antibody by anticomplementary activity in the CF test system. Staining of immunoprecipitates in the IEOP test contributed little to the sensitivity of the test for detection of HAA.

Animals↗
PubMed1971

Evaluation of enterovirus immune horse serum pools for identification of virus field strains.

Immune horse sera to 42 enterovirus immunotypes were pooled according to the Lim Benyesh-Melnick and the "intersecting serum" schemes. Each serum was diluted in the pools to contain 50 antibody units. After it was established that the pools correctly neutralized prototype virus strains, they were evaluated in tests against 273 enterovirus field strains representing most of the viral types included in the pools. With test virus doses of 10-100 TCD(50), most of the poliovirus and coxsackievirus field strains were correctly identified in both schemes, but a number of the echoviruses were neutralized by heterotypic pools, particularly in the Lim Benyesh-Melnick scheme. However, at higher test virus doses of 320-3200 TCD(50), little heterotypic neutralization occurred in either scheme, and 93-94% of the virus field strains were correctly identified in each scheme. With these larger virus doses, breakthrough tended to occur in homologous pools by the 7th day, but rarely by the 5th day. Since the Lim Benyesh-Melnick pool scheme employs 8 pools as compared with 13 for the intersecting serum scheme, and since the two schemes were equally satisfactory for identifying virus field strains at test virus doses of 320-3200 TCD(50), immune horse sera will be pooled by the former scheme, thus utilizing fewer pools, for distribution to qualified viral diagnostic laboratories.

Animals↗
PubMed1971

Comparison of various methods for preparation of viral serological antigens from infected cell cultures.

In efforts to prepare more potent and sensitive viral serological antigens, several aspects of the production of antigens from infected cell cultures were studied. Antigens derived from whole, infected culture material and from the cellular and fluid phases were compared. Freezing and thawing, sonication, and alkaline buffer extraction were compared for effectiveness in releasing antigen from host cells. The effect of the multiplicity of infection on titers of viral antigens produced in cell cultures was studied. Generally, higher titered antigens were derived from the infected cells than from the culture fluids, but for certain viruses complement-fixing (CF) antigens derived from the culture fluids gave higher antibody titers than did cell-associated antigens. With each virus-host cell system studied, treatment with alkaline buffers extracted appreciable amounts of CF antigen from the host cells, but in some instances more antigen was released by freezing and thawing or by sonication. Extraction of infected cells with alkaline buffers was not a satisfactory method for preparation of hemagglutinating (HA) antigens for any of the viruses studied. The highest-titered HA antigens were produced from infected cells disrupted by freezing and thawing or sonication. The highest titered CF and HA antigens were produced from cell cultures infected at multiplicities of one or greater. Complement-fixing antigens produced by infecting cells in suspension and then planting had lower titers than antigens produced in parallel by infecting developed monolayers. Optimal methods are summarized for preparation of serological antigens to a variety of viruses of man.

Animals↗
PubMed1970

Variables of the rubella hemagglutination-inhibition test system and their effect on antigen and antibody titers.

A systematic study was made of certain variables of the rubella hemagglutination-inhibition (HI) test system and their effect on antigen and antibody titers. Erythrocytes from pigeons and 1-day-old chicks gave similar antigen and antibody titers, but goose erythrocytes gave lower titers. Indicator erythrocytes could be stored in Alsever's solution at 4 C for as long as 2 weeks without losing sensitivity in hemagglutination (HA) and HI tests. Antigen titers varied by eightfold or more in different diluent systems; titers were generally higher at pH 6.2 than at pH 7.2. A diluent without Ca(2+) gave antigen titers as high as those obtained in diluents with added Ca(2+) ions. Antibody titers also varied in different diluent systems. HEPES diluents at pH 6.2 gave higher antibody titers than those obtained in other diluents, but occasional "false-positive" inhibition reactions were seen. Kaolin suspended in borate saline at pH 9.0 effectively removed inhibitor from sera without absorbing specific antibody, but at pH 7.3 it removed various amounts of specific antibody. Antibody titers of sera treated with kaolin at pH 9.0 were similar to those of sera treated with heparin-MnCl(2); treatment with dextran sulfate-CaCl(2) gave lower antibody titers. Antigens varied widely in sensitivity for detecting HI antibody and in the ability to detect diagnostically significant increases in antibody. Sensitivity in detecting antibody was not related to the HA titer of the antigens. Tween-ether-treated antigens gave lower antibody titers but were more reliable than corresponding untreated antigens for serological diagnosis of infection.

Animals↗
PubMed1969

Enzymes produced by a Pseudomonas species which inactivate inhibitors of certain viral hemagglutinins. I. Identification and purification of a proteinase and phospholipase C.

Filtrates from cultures of a psychrophilic Pseudomonas species, which inactivate serum inhibitors of certain viral hemagglutinins, were shown to contain both lecithinase (phospholipase C) and a proteolytic enzyme with elastase activity. The bacterium was cultivated under conditions favoring production of the respective enzymes, and the enzymes were purified by ammonium sulfate precipitation followed by column chromatography or by gel filtration. The elastase was obtained in crystalline form and was recrystallized. It has properties similar to those of a number of other bacterial elastases but is more heat-labile than most. Although a high degree of purification was achieved for the lecithinase, as evidenced by an increase in specific activity, it was not obtained in crystalline form. Partially purified preparations of the lecithinase had extremely high activity compared to that of commercial preparations of phospholipase C from Clostridium welchii.

Chemical Precipitation↗
PubMed1969

Rubella. Technical problems in the performance of hemagglutination-inhibition (HI) tests.

The rubella hemagglutination inhibition (hi) test is the most sensitive serologic method available for diagnosis of infection and for determination of immunity status. At present, however, it is not a well-standardized procedure and several modifications are in use. Comparison of results obtained on the same specimens by different laboratories has shown wide variations. The sensitivity and reliability of the technique is decidedly influenced by each of the variables of the test system; these include erythrocytes, antigen, methods employed for removal of non-specific inhibitors and natural agglutinins from test sera, the pH of the diluents and the temperature of incubation. The presence or absence of hi antibody cannot be determined reliably by screening a single low dilution of serum. Commercially available reagents and kits for rubella hi tests vary widely in their reliability. The test should be performed only by experienced persons who understand the principles of the technique and who are aware of the pitfalls and of the importance of using adequate controls in each run.

Hemagglutination Inhibition Tests↗