Cross-reactivity and antigenic heterogeneity among Actinobacillus pleuropneumoniae strains of serotypes 4 and 7.

Actinobacillus pleuropneumoniae strains of serotypes 4 and 7 were studied for their antigenic properties by means of agglutination, coagglutination, indirect hemagglutination, immunodiffusion, and counterimmunoelectrophoresis tests. Strains of serotype 4 showed cross-reactivity with those of serotype 7 in various serological tests. Serotype 7 strains were antigenically heterogeneous and shared common antigens with several other serotypes. By using boiled whole-cell saline extract as the antigen in the immunodiffusion test, serotype 7 strains could be divided into four subgroups. Subgroup I strains did not have antigens in common with other serotypes, whereas subgroup II strains had antigens in common with serotype 4; subgroup III strains had antigens in common with serotype 10, and subgroup IV had antigens in common with serotypes 1, 9, and 11. The indirect hemagglutination test using unheated whole-cell saline extract as the antigen detected serotype-specific activity. Quantification of serotype-specific and group-specific antigens by coagglutination and immunodiffusion tests was found useful for identifying strains that belonged to serotype 4 or 7.     

Identification and serotyping of Haemophilus pleuropneumoniae by coagglutination test

A coagglutination test for the identification and serotyping of Haemophilus pleuropneumoniae is described. A total of 360 H. pleuropneumoniae strains were isolated from pulmonary tissues of feeder pigs which died of acute pleuropneumonia. All of the isolates were serotyped by coagglutination, and the results were confirmed by the ring precipitation test. The most common serotype isolated in Quebec was serotype 1, followed by serotypes 5, 2, and 7. None of the isolates belonged to serotypes 3, 4, or 6. Mixed infections due to H. pleuropneumoniae of more than one serotype in the same animal were encountered. Serotype 1 was the only common isolate among the mixed-serotype infections. The coagglutination test was more sensitive than was the ring precipitation test. Serotyping by the coagglutination test is inexpensive, rapid, reliable, and easy to perform.     

Modified colony indirect epifluorescence test for serotyping Ureaplasma urealyticum and an adaptation to detect common antigenic specificity.

A microtiter method for efficiently serotyping colonies of Ureaplasma urealyticum by immunofluorescence is described. Prior detergent treatment allowed identification of common group determinants.     

Cross-reactions between Actinobacillus (Haemophilus) pleuropneumoniae strains of serotypes 1 and 9.

Actinobacillus pleuropneumoniae strains of serotypes 1 and 9 were studied for their serological properties by means of agglutination, coagglutination (CoA), indirect hemagglutination (IHA), Co-IHA, ring precipitation (RP), and immunodiffusion (ID) tests. Particulate and soluble antigens of unheated and heat-treated bacterial cells were used in various serological tests. Agglutination, CoA, and RP tests demonstrated common antigens between strains of serotypes 1 and 9. Quantitative estimation of serotype-specific antigenic activity by CoA, RP, and ID tests proved useful in differentiating strains of serotypes 1 and 9. IHA and Co-IHA tests using sheep erythrocytes sensitized with unheated or heat-treated whole-cell saline extract and the ID test using boiled whole-cell saline extract as antigen distinguished the strains of serotypes 1 and 9. In studies of absorption of rabbit antisera with heterologous whole-cell antigens there was no absorption of antibodies in tube agglutination and IHA tests, suggesting that serotype 1 and 9 strains belong to two distinct serogroups. It appears that the cross-reactivity between serotype 1 and 9 strains could be due to common epitopes associated with cell wall antigens.     

Evaluation of an indirect hemagglutination test for the diagnosis of human leptospirosis.

A presumptive hemagglutination test for the serological diagnosis of leptospirosis in humans is described. The antigen was prepared from a soluble alcohol extract of an andamana strain sorbed to human O-negative erythrocytes and preserved by pyruvic aldehyde fixation. In this study, the overall sensitivity of the hemagglutination test was 92% in contrast to 69% for the presumptive slide agglutination test. The specificity was 95% for the hemagglutination test in comparison with 83% for the slide test.     

Freeze-dried erythrocytes for an indirect hemagglutination test for detection of cytomegalovirus antibodies.

An indirect hemagglutination test with lyophilized, fixed, tanned, and cytomegalovirus (CMV)-sensitized sheep erythrocytes for the detection of CMV antibodies is reported. To avoid nonspecific hemagglutination, cells were fixed with glutaraldehyde or Formalin directly in whole blood. The lyophilized, CMV-sensitized erythrocytes obtained by this technique were stable up to 9 months at 37 degrees C and retained the same reactivity at fresh, CMV-sensitized cells. Indirect hemagglutination performed with lyophilized, sensitized cells was highly efficient in detecting CMV-antibodies as compared with complement fixation and enzyme immunoassay.     

Value of indirect hemagglutination and coagglutination tests for serotyping Haemophilus parasuis

An indirect hemagglutination test (IHA) and a coagglutination test (CA) were evaluated using saline, boiled, and autoclaved extracts for serotyping Haemophilus parasuis. CA showed several cross-reactions, whereas IHA gave rise to specific reactions, with minor exceptions. IHA was further compared with the immunodiffusion test (the "gold standard") for the serotyping of 67 field isolates. As a conclusion, IHA is recommended as a useful method for sensitive and specific serotyping of H. parasuis.     

Serotype specificity and immunogenicity of the capsular polymer of Haemophilus pleuropneumoniae serotype 5.

Serotyping of Haemophilus pleuropneumoniae and serologic assays for detection of serotype-specific antibody are problematic due to the potential cross-reactivity of the crude antigens used for raising immune serum or for serology. The capsular polymer (CP) of H. pleuropneumoniae serotype 5 was investigated for serotype-specific activity with antiserum to whole cells or with antiserum made monospecific to CP by adsorption with a capsule-deficient mutant. When antiserum to whole cells or monospecific antiserum to CP was tested against purified CP from serotypes 1 to 7 by immunodiffusion or enzyme-linked immunosorbent assay, only capsules of serotype 5 were reactive. In addition, only encapsulated serotype 5 cells reacted with serum monospecific to CP in an indirect immunofluorescent-antibody assay. Serotype-specific antibody was completely inhibited in each assay by preincubation of purified CP with the serum. Antiserum to whole cells of H. pleuropneumoniae serotype 5 contained antibodies to proteins and lipopolysaccharide; these antibodies cross-reacted with antigens of heterologous serotypes by dot-blot enzyme-linked immunosorbent assay and immunoblotting. The antigenic activity of CP was stable after heating for at least 30 min at 100 degrees C. High titers of antibody to CP were present in the sera of rabbits immunized intravenously with whole log-phase cells or in the convalescent sera of pigs experimentally infected with H. pleuropneumoniae serotype 5. However, the purified CP was poorly immunogenic in rabbits and swine. Our results indicate that the capsule is the serotype-specific antigen of H. pleuropneumoniae and that a monospecific antiserum to capsule or purified capsule should be used for serotyping or serologic assays, respectively.     

Rickettsial indirect hemagglutination test: isolation of erythrocyte-sensitizing substance.

The erythrocyte-sensitizing substances (ESS) of Rickettsia prowazekii and R. conorii were characterized by biological and chemical criteria. ESS could be derived from either soluble or particulate complement-fixing antigens obtained by ether extraction of rickettsiae. The soluble complement-fixing antigen exhibited two peaks of serological activity in potassium tartrate density gradients. The particulate complement-fixing antigen coincided with the more dense peak but was distinguishable by its sedimentation in rate-zonal sucrose gradients. ESS was obtained from each of the complement-fixing-reactive gradient peaks by extraction with hot alkali and was quantified by a modified indirect hemagglutination test. These ESS preparations sedimented similarly in potassium tartrate gradients and were shown to contain protein and carbohydrate, both by colorimetric tests and by incorporation of radioactive precursors. The serological activity of ESS was unaffected by trypsin, but both antigenicity and erythrocyte-binding capacity were reduced after exposure to sodium metaperiodate. Highly purified ESS was rapidly inactivated by potassium tartrate and required stabilization with bovine plasma albumin.     

Evaluation of a modified complement fixation test and an indirect hemagglutination test for the serodiagnosis of melioidosis in pigs.

A complement fixation test modified by the addition of porcine serum and an indirect hemagglutination test were used to detect antibodies to Pseudomonas pseudomallei in pigs. These tests together with cultural examinations were carried out with 250 pigs. The sensitivity and specificity values were 79.3 and 99.5% and 82.8 and 93.2% for the modified complement fixation and hemagglutination tests, respectively. When results from the combination of both tests were considered, the values were 86.2 and 92.8%, respectively.     

Evaluation of an indirect hemagglutination test for Legionella pneumophila serogroups 1 to 4

Parallel testing of 895 sera by indirect hemagglutination and indirect fluorescent-antibody techniques showed 97.3% agreement. Although the indirect hemagglutination technique usually showed more cross-reactivity among serogroups than the indirect fluorescent-antibody technique with Formalin-fixed antigens and a conjugate which detected primarily immunoglobulin G antibodies, heterologous serogroup reactions were significantly lower than homologous serogroup titers and the etiological serogroup could be easily defined. The indirect hemagglutination techniques showed no cross-reactivity with a crude extract of Escherichia coli O13:K92:H4. Since the indirect hemagglutination technique was shown to detect both immunoglobulin M and immunoglobulin G antibodies and was found to be rapid, simple, and inexpensive, it appears to be an excellent alternative to the indirect fluorescent-antibody test for serodiagnosis of legionellosis.     

Detection of cytomegalovirus antibody with two commercially available assays, an indirect hemagglutination test and an enzyme immunosorbent assay.

By the use of two reference procedures, an indirect hemagglutination assay and a complement fixation test, the presence or absence of cytomegalovirus (CMV) antibody was determined for 221 human sera. Ninety-nine sera (44.8%) were found to contain CMV antibody. The remaining 122 sera (55.2%) lacked detectable CMV antibody. These same sera were then analyzed by two recently introduced, commercially available CMV antibody assays, an indirect hemagglutination test (IHA-c; Cetus Corp., Emeryville, Calif.) and an enzyme-linked immunosorbent assay (ELISA; M. A. Bioproducts, Walkersville, Md.). With the results of the reference procedures as true evidence of the presence or absence of CMV antibody, the sensitivity of the IHA-c was found to be 100%; the specificity was 98.4%. The sensitivity of the ELISA was also 100%; the specificity was 96.7%. The overall accuracies of these procedures were 99.1 and 98.2%, respectively. Time and motion studies revealed the IHA-c procedure to be faster and technically less demanding than the ELISA procedure.     

Detection of rubella antibodies by hemagglutination inhibition, indirect fluorescent-antibody test, and enzyme-linked immunosorbent assay.

Using hemagglutination inhibition (HAI) as a reference method, 292 (40 nonimmune, 252 immune) human serum samples were tested by indirect fluorescent antibody (IFA) and enzyme-linked immunosorbent assay (ELISA) for immune status and quantitation of rubella antibodies. The overall agreement with HAI for immune status was 99.7% (291/292) with IFA and 98.6% (288/292) with ELISA. Two specimens (0.7%, 2/292), negative by HAI, were equivocal by ELISA. Initially a 6.5% (19/292) overall disagreement was obtained for immune status evaluation between HAI and IFA, which was reduced to 0.3% (1/292) upon repeat testing. All of these samples were near the immune/nonimmune cutoff point (95 samples), reflecting an initial disagreement of 20% (19/95) in this category (HAI titers less than 1:20). Likewise, an initial overall disagreement of 4.5% (13/292) was obtained between HAI and ELISA which was reduced to 0.7% (2/292) upon repeated testing. Eleven of the 13 samples were near the immune/nonimmune cutoff point, reflecting an initial disagreement of 11.6% (11/95) with sera having an HAI antibody titer of less than 1:20. Quantitation of rubella antibodies by IFA showed an overall correlation with HAI of 86.6% within less than twofold titer and 99.3% within less than fourfold titers. In testing the ability of ELISA to quantitate antibody, a correlation coefficient (r) of 0.996 was obtained by plotting the measured average optical density (405 nm) of ELISA against the corresponding log of HAI titer. Both IFA and ELISA showed good correlation with HAI for immune status evaluation and for quantitation of rubella antibodies. Technically the HAI was the most cumbersome to perform, whereas IFA was the least technically demanding. Originally, 308 samples were tested; 16 samples (5.2%) could not be evaluated by IFA because of a high level of nonspecific fluorescence. The strict requirement of controlling the temperature range (23 to 24 degrees C) during substrate hydrolysis proved to be a problem with the ELISA test in our laboratory.     

Modified indirect hemagglutination test for detection of treponemal antibodies in finger-prick blood.

A modified indirect hemagglutination test for the detection of treponemal antibodies was developed for use with finger-prick blood. By using paired serum and absorbed finger-prick blood from 58 patients from an area previously endemic for yaws and 12 patients without yaws, the modified hemagglutination test was compared with a hemagglutination test for Treponema pallidum and the fluorescent treponemal antibody absorption test. The modified hemagglutination test showed 100% specificity and an overall agreement of 96.5% with the hemagglutination test for T. pallidum and 94.8% with the fluorescent treponemal antibody test. The modified hemagglutination test appears to be a simple and economical test that is suitable for use in large epidemiological surveys for yaws.     

Outer membrane protein profiles of Haemophilus pleuropneumoniae.

Outer membrane protein profiles of Haemophilus pleuropneumoniae were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cells were disrupted by sonication, and outer membrane-enriched fractions were prepared by differential centrifugation and selective solubilization of the inner membrane with sodium N-lauroyl sarcosinate. Colony type, growth medium, time of harvest, and in vitro or in vivo passage had no appreciable effect on the protein profiles of the strains examined. Seven patterns were distinguished among the reference strains of the nine capsular serotypes. These patterns were based on the mobility of the major outer membrane proteins migrating in the 39,000- to 44,000-molecular-weight region of the gel, a 16K to 16.5K protein, and a heat-modifiable 29K protein. Strains of serotypes 1 and 9 had identical outer membrane protein profiles, as did strains of serotypes 2 and 6. The reference strains of the remaining five serotypes each had a distinct pattern. The outer membrane protein profiles of 95 field isolates belonging to serotypes 1, 5, 7, and 9 from swine in the midwestern United States were determined and compared with the reference patterns. The results indicate that the population of H. pleuropneumoniae is clonal, with three predominant clones distinguished by both serotype and outer membrane protein profile responsible for the majority of H. pleuropneumoniae disease occurring in swine in the United States.     

Improved indirect hemagglutination test for cytomegalovirus using human O erythrocytes in lysine.

A modified indirect hemagglutination test for cytomegalovirus antibodies is described in which glutaraldehyde-fixed human O cells, rather than sheep cells, are used. Nonspecific hemagglutination was reduced by use of the optimal tannic acid concentration for each cell batch and the addition of 0.1 M lysine to the phosphate-buffered saline in which the fixed, tanned, sensitized cells were resuspended for use in the test. Three of 349 sera showed nonspecific hemagglutination by this technique. Antigen made by freezing phosphate-buffered saline (pH 7.2) over an infected monolayer can be used at dilutions of 1:8 to 1:15. Fixed, tanned, sensitized cells ready for use in the test can be stored in liquid nitrogen for up to 8 months. Use of cryoprotectants and washing after thawing is unnecessary. Simplification of the assay permits one person to screen 300 sera in 1 day or to determine the immune status of a potential donor or recipient in 45 min after the test is set up. The modified assay compares favorably in sensitivity with the complement fixation test and with previously described methods for performing the indirect hemagglutination test.