Evaluation of a new enzyme immunoassay (TESTPACK rotavirus) for the detection of rotavirus in fecal specimens.

One hundred and forty fecal specimens were tested for rotavirus using two immunoassays, TESTPACK Rotavirus and Pathfinder Rotavirus. Five discordant specimens were evaluated by a blocking assay. The sensitivity, specificity, positive predictive value, and negative predictive value were 98, 100, 100, and 99% for TESTPACK and 92, 100, 100, and 96% for Pathfinder, respectively.

Interaction of bovine immunoglobulin gamma 2 (IgG2) with staphylococcal protein A: evidence for IgG2a and IgG2b sub-subclasses in the bovine.

The reactivity of bovine IgG with protein A is confusing with respect to which of the bovine IgG class and subclasses are reactive. We have, therefore, re-examined the interaction of bovine immunoglobulins with protein A. The results presented in this paper indicated that at pH 8.0 protein A binds only immunoglobulin of the IgG2 subclass. The bound IgG2 can be readily recovered from an immobilized protein A column at pH 5.0. Furthermore, the antigenic IgG2 eluted demonstrated two charged species which could readily be separated by ion-exchange chromatography. These results indicate that IgG2 in the bovine exists in two sub-subclasses, IgG2a and IgG2b. The two sub-subclasses of IgG2 could be rapidly isolated with a good yield in two-steps namely protein A affinity chromatography followed by ion exchange chromatography.

Solid-phase radioimmunoassay for the detection of immunoglobulins against bovine Brucella abortus.

A sensitive radioimmunoassay for the detection of Brucella abortus antibody is described. The assay, performed in flexible 96-well microplates coated with Brucella abortus antigens, utilizes 125I-labeled staphylococcal protein A to detect antibody to Brucella abortus. The parameters of the assay have been analyzed using well recognized statistical methods. Least squares analysis of antigen concentration, antiserum dilution, antigen by antiserum and replicates within antigen by antiserum, estimated an r2 of 0.98, a coefficient of variation of 3.58 and a standard deviation of 0.10. Results of regression analysis of serum dilution versus antigen concentration (ranging from 635 micrograms/ml to 6.35 ng/ml) indicated that an antigen concentration of 6.35 micrograms/ml was the most efficient for describing antibody variability (r2 = 0.98, with a coefficient of variation = 3.28). Regression analysis also revealed a closer correlation between the radioimmunoassay with complement fixation test (r2 = 0.98) than with the standard tube test (r2 = 0.84). Detection of specific antibody assessed by radioimmunoassay was 4 to 64 fold more sensitive than the standard tube test titer and 16 to 32 fold more sensitive than the complement fixation test titer. The results described here indicate that this radioimmunoassay is very sensitive and may be capable of discriminating between false positives and false negatives, thereby, improving the diagnostic efficiency of Brucella serologic tests.

Comparison of nine commercial immunoassays for the detection of rotavirus in fecal specimens.

One hundred fecal specimens obtained from patients with acute gastroenteritis were tested for rotavirus with nine commercial immunoassays to evaluate the sensitivity, specificity, predictive value, and diagnostic accuracy of these assays. Kits evaluated included two monoclonal antibody-based enzyme immunoassays (EIAs) (Rotaclone and Pathfinder Rotavirus), three polyclonal antibody-based EIAs (Rotavirus Immunoassay, Rotazyme II, and Wellcozyme Rotavirus), and four latex agglutination assays (Rotastat, Virogen Rotatest, Meritec-Rotavirus, and The Wellcome Latex Test). Thirty-eight of the 100 specimens were found to contain rotavirus by a reference microplate EIA. The accuracy of the reference assay was determined by RNA electrophoresis and a blocking assay on discordant specimens. The two monoclonal antibody EIAs had superior sensitivities (100%) and identified two positive specimens which were negative by the reference method but positive by the blocking assay. Among the polyclonal EIAs, all had sensitivities of greater than 90%, but specificities were variable; Rotazyme II, with a specificity of 50%, showed considerable discrepancy from other polyclonal EIAs. The latex tests had sensitivities ranging from 70 to 90% and specificities of 80 to 100%. Latex agglutination tests were more rapid than EIAs and did not require expensive equipment. The final choice of assay system will depend on the cost, speed, and accuracy requirements of the clinical laboratory.

Choice of reference assay for the detection of rotavirus in fecal specimens: electron microscopy versus enzyme immunoassay.

Two previously demonstrated sensitive and specific enzyme immunoassays (EIAs) for rotavirus, one using polyclonal and monoclonal antisera (TestPack Rotavirus [TPK]; Abbott Laboratories) and the other using only monoclonal anti-rotavirus antibodies (Rotaclone [RTC]; Cambridge BioScience Corporation), were evaluated as potential reference assays for rotavirus testing in comparison with direct negative-staining electron microscopy (EM), the current laboratory standard. Two hundred and seven stool samples collected consecutively during the winter of 1989 from children with acute diarrhea admitted to a ward for infants from 0 to 2 years of age were tested by the EIAs and by EM. TPK specimens were read visually; RTC results were read spectrophotometrically. Specimens with discordant EIA and EM results were further evaluated by a fluorescent focus assay. Specimens positive by EM and those negative by EM but positive by fluorescent focus assay were considered to be positive for rotavirus. Of the 207 stools tested, 35 (17%) were positive for rotavirus by these criteria. EM had a sensitivity of only 80%. Specificities were 100% for RTC and EM and 89% for TPK. These findings indicate that EM, although very specific, is relatively insensitive compared with a highly sensitive monoclonal antibody-based EIA. An EIA with high sensitivity and specificity, such as RTC, is a more appropriate reference standard for rotavirus testing.