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Rubella hemagglutination-inhibition test: false-positive reactions in sera contaminated with bacteria.

We have shown that bacterial contamination of sera can have a marked influence on the results of the rubella hemagglutination-inhibition (HI) test. In addition to increasing the levels of nonspecific agglutinins, a number of common bacterial species tested had a significant effect on the HI titers. When sera free from rubella-specific antibodies were contaminated with Bacillus subtilis or Pseudomonas fluorescens, HI titers ranged from 16 to 128 (expressed as the reciprocal of the highest serum dilution completely inhibiting hemagglutination) after treatment with heparin/MnCl2. Our observations demonstrate, therefore, that bacterial contamination can be one of the causes of false-positive reactions in this test.

Bacillus subtilis↗

Standardized viral hemagglutination and hemagglutination-inhibition tests. I. Standardization of erythrocyte suspensions.

A spectrophotometric procedure for standardizing red blood cell suspensions for use in viral hemagglutination tests is described. The procedure is based on highly reproducible cyanmethemoglobin absorbance readings at 540 nm on any suitable spectrophotometer. Target values for milligrams of cyanmethemoglobin per 100 ml are given for the red cell suspensions of all mammalian and avian species employed in viral hemagglutination tests. By use of these values and a cyanmethemoglobin standard curve for a particular photometer, approximate 4% erythrocyte suspensions can be diluted to any lesser concentration. Coefficients of variation for the various diluted suspensions range from 4 to 7%.

Animals↗

Evaluation of the hemagglutination-inhibition test for measuring the response of chickens to avian infectious bronchitis virus vaccination.

An infectious bronchitis virus (IBV) hemagglutination-inhibition (HI) test was used to assay serum-antibody titers after IBV vaccination of IBV-susceptible specific-pathogen-free broilers and commercial layers. Three-week-old broilers were vaccinated via eye-drop with IBV strains that represent the antigenic spectrum of commercial vaccines--Holland, Massachusetts 41 (41 Ms), Connecticut 46, Florida 18288, or JMK strain--and revaccinated 3 weeks later with either the same or a heterologous strain. Weekly serum samples were tested by IBV HI with homologous and heterologous antigens. Vaccinates, except for those vaccinated with the Holland strain, were HI-positive with homologous but not heterologous antigens by 1 to 2 weeks postvaccination. Sixteen-week-old IBV-vaccinated commercial layers were revaccinated with IBV Holland 52 (H 52) strain and subsequently infected with Arkansas 99 (Ark 99) and SE 17 strains. In contrast to the limited HI cross-reactivity of serum from IBV-vaccinated broilers, there were extensive cross-reactions in HI tests with 41 Ms, H 52, Ark 99, and SE 17 antigens of revaccinated layers. These results demonstrate that the IBV HI test is more strain-specific than previous reports indicate, especially when the test samples are from early postvaccination.

Animals↗