Zhongguo shuxue zazhi (Oct 2022)
Establishment and evaluation of a fluorescent antibody assay against varicella-zoster virus membrane antigen based on Vero E6 cells
Abstract
Objective To establish and evaluate a fluorescent antibody to membrane antigen (FAMA) method for detecting antibodies against varicella-zoster virus (VZV) based on Vero E6 cells. Methods Based on the adapted VZV-Oka-E6 strain that VZV-Oka live attenuated varicella vaccine strain grew in Vero E6 cells, Vero E6 cells were infected with VZV-Oka-E6 of three different doses (104.65, 104.95 and 105.25 TCID50), and the cytopathic effect was observed under a microscope to determine the optimal infection dose of VZV-Oka-E6 strain. Then the detectable sensitivity of the infected cell antigen slides prepared after fixing the infected cells with different fixatives was compared to determine the optimal fixative. As a result, the FAMA method based on Vero E6 cells for the determination of neutralizing anti-VZV has been developed. The established FAMA assay was used to detect the international standard for varicella zoster immunoglobulin with different titers to determine the sensitivity of the assay. The specificity of the assay was evaluated by detecting specific antibodies against human herpes simplex virus (HSV) type 1 and type 2. The neutralizing anti-VZV antibodies of the international standard for varicella zoster immunoglobulin were detected using VZV-infected cell antigen slides prepared in the same batch and four different batches, respectively, to determine the intra-assay repeatability and inter-assay repeatability. The international standard for varicella zoster immunoglobulin with three known titers was detected to evaluate the relative accuracy of this assay. The anti-VZV titers in 20 apheresis plasma samples were determined with the newly established FAMA test and ELISA test, respectively, and the detection results of the two methods were compared using Spearman’s correlation test. Results The optimal infection dose of the VZV-Oka-E6 strain in FAMA assay was determined to be 105.25 TCID50, and acetone precooled at -20℃ was used as the fixative. The FAMA test has a high sensitivity with a detecting limit of 31.25 mIU/mL for neutralizing anti-VZV titers. The negative result was observed when detecting herpes simplex virus (HSV) type 1 and 2 specific antibodies. The international standard for varicella zoster immunoglobulin was detected by VZV infected cell antigen slides prepared in the same batch and 4 different batches, with the coefficient of variation being 29.95% and 26.71%, respectively. The detection value of the international standard for varicella zoster immunoglobulin with three different titer levels was consistent with their theoretical value. The correlation coefficient of the detection results of 20 apheresis plasma samples by the FAMA test and ELISA test was 0.268. Conclusion The VZV FAMA assay has good sensitivity, specificity, repeatability, and relative accuracy in detecting neutralizing anti-VZV titers. It can be applied for detecting neutralizing anti-VZV titers in apheresis plasma samples as well as the varicella-zoster immunoglobulin (VZIG) preparations.
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