Assessment of pyrogenic response of lipoteichoic acid by the monocyte activation test and the rabbit pyrogen test.

Lipoteichoic acid (LTA) is a non-endotoxin pyrogen of a great importance in the pathogenesis of sepsis. The Rabbit Pyrogen Test (RPT) is able to detect all types of pyrogens but involves the use of animals. The Bacterial Endotoxin Test (BET) cannot fully replace the RPT because it only detects endotoxins. The Monocyte Activation Test (MAT) is sensitive to all types of pyrogens and it is based on the same biological mechanism that is responsible for the fever reaction in humans. Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) has recommended its use for other pyrogens than endotoxin because its equivalence to RPT can be demonstrated. The aim of this study was to evaluate the pyrogenic responses of the RPT and MAT that was induced by LTA. Different LTA concentrations were assayed by the MAT in parallel to the RPT. The results showed that the MAT was more sensitive than the RPT, demonstrating that the MAT detected LTA. This result may contribute to the acceptance of this test by the Brazilian regulatory agencies as a replacement for the animals used in the RPT.

Potency evaluation of rabies vaccine for human use: the impact of the reduction in the number of animals per dilution.

In order to evaluate the effects of reducing the number of animals used in the NIH mouse protection test for potency determination of inactivated rabies vaccines for human use, a retrospective study of the results obtained in the Brazilian National Control Laboratory, Instituto Nacional de Controle de Qualidade em Saúde (INCQS), was performed, comprising 214 vaccine lots. The INCQS Standard Operating Procedure establishes the use of three vaccine dilutions and 18 animals per dilution, separated into two cages with 9 mice each. The results of the two cages of each dilution were considered as two different groups (C1 and C2), and therefore, for each vaccine lot, three results were obtained: one for the standard test (ST) with 18 mice, one using the C1 cages with 9 mice and another using the C2 cages with 9 mice. The results were evaluated as repeated measures of the same method on the same samples. In this study, the effects of the reduction in: (a) the measurement error and its association with the size of measurement, (b) the agreement between the results using the concordance coefficient of correlation, (c) the agreement of categorized results as "Pass" or "Fail" using the Kappa index, (d) the precision of potency determinations using the 95% confidence interval and (e) the incidence of statistically invalid assays due to non-linearity and non-parallelism were evaluated. It was concluded that the results from the NIH mouse protection test using 9 mice per dilution are in good agreement with the results obtained using 18 mice per dilution. Therefore, nine animals per dilution is a suitable number to meet the statistical requirement for valid assays.

Validation of a virus neutralization potency test in BHK-21 cells for rabies immunoglobulins in a two-center study.

A rabies virus neutralization potency test (VNPT), adapted to microplates from the rapid fluorescent focus inhibition test (RFFIT) for rabies therapeutic immunoglobulin potency evaluation, was standardized and validated in a two-center study in Brazil. The two institutes involved in the study were: Instituto Nacional de Controle de Qualidade em Saúde (Fundação Oswaldo Cruz) and Instituto Butantan. Two equine rabies immunoglobulin samples, all diluted to 1IU/ml, were tested against the WHO 2nd Rabies Human Ig International Standard. Four dilutions of the samples and standards were tested with the VNPT. The potency of the samples was calculated in IU/ml using the probit method; linearity, accuracy, repeatability (intra-assay variation), intermediate precision (inter-assay variation) and reproducibility (inter-laboratory variation) were assessed to evaluate the reliability of the VNPT. Laboratories were arbitrarily coded as Laboratory A and Laboratory B. The following results were obtained with the International Standard: (a) linearity, the overall coefficient of correlation of the dose-response curve was -0.97; (b) accuracy, % error of -0.70 (IU/ml); (c) repeatability, 17.06% (Laboratory A) and 11.61% (Laboratory B); (d) intermediate precision, 16.99% (Laboratory A) and 22.05% (Laboratory B); (e) reproducibility, 14.5%. The final conclusion was that VNPT presents satisfactory linearity, accuracy, repeatability, intermediate precision and reproducibility and is a reliable and suitable method by which to evaluate rabies immunoglobulin potency.