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@#Objective To prepare the second generation internal control reference(B2)for Ig G antibody against severe acute respiratory symptom coronavirus 2(SARS-CoV-2)and evaluate its applicability in ELISA detection method. Methods Among the volunteers vaccinated with SARS-CoV-2 inactivated vaccine(BBIBP-Cor V)produced by Beijing Institute of Biological Products Co.,Ltd.,19 Ig G antibody positive plasma samples with ELISA-Ig G dilution ratio of 20 ～ 60 were screened,and the Ig G antibody,IgM antibody and neutralizing antibody were detected by ELISA,B2 was prepared from nonlipid plasma with ELISA-Ig G dilution ratio of 32 ～ 45,IgM negative and similar neutralizing antibody inhibition rate. The neutralizing antibody potency of the first generation internal control reference(B1)and B2 detected by ELISA was calibrated with the first generation WHO international standard of anti-SARS-CoV-2 immunoglobulin(NIBSC 20/136),and the accelerated stability(storage at 2 ～ 8 ℃ for 5,8,14,20,and 30 d respectively),the service stability(storage at 18 ～25 ℃ for 1,2,and 3 h respectively),the freeze-thaw stability(1,2 and 3 times)and the long-term stability(storage at-25 ℃ for10 months)of B2 were tested. B2 was used as standard to detect plasma after single vaccine immunization and mixed plasma was prepared according to different ELISA-Ig G dilution ratio. The correlation and linear regression analysis between ELISA-Ig G dilution ratio and neutralizing antibody potency of pseudovirus in mixed plasma were carried out. Results Among 19 plasma samples,5 samples were non-lipid plasma with ELISA-Ig G dilution ratio of 32 ～ 45,IgM negative and similar neutralizing antibody inhibition rate. B2 was prepared by mixing every plasma in equal volume fraction,and the dilution ratio of ELISA-Ig G was assigned to 32. The neutralizing antibody potency of B1 calibrated with NIBSC 20/136 was 133. 38 EIU/m L and that of B2 was 122. 14 EIU/m L. The recovery rates of accelerated stability,service stability,freeze-thaw stability and long-term stability of B2 were all in the range of(100 ± 15)%. The ELISA-Ig G dilution ratio of the mixed plasma from the same source was significantly correlated with the neutralizing antibody potency of pseudovirus.(each R~2> 0. 99,each P < 0. 000 1).Conclusion B2 prepared from plasma immunized with SARS-CoV-2 inactivated vaccine can replace B1 prepared from plasma of COVID-19 convalescent patients.
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【Objective】 To determine the ELISA kit for screening convalescence plasma with high potency of SARS-CoV-2 IgG by comparing and analyzing the plasma detection results of convalescent plasma collected in different periods via ELISA kits from two manufacturers and the results of mixed plasma with different potency via pseudovirus neutralization experiments. 【Methods】 Two ELISA kits from different manufacturers(named A, B) were used to detect the plasma of 269 convalescent patients collected from Feb.2020~Jan.2022. The correlation and concordance rate of the two results were analyzed to determine the kit preliminarily. According to the titers of diluted series of standard of the preliminary selected kit, 5 mixed plasma samples (G4-G128) with different potency were prepared. The correlation of ELISA IgG results of product A/B, as well as the pseudovirus neutralization test of the original strain, Omicron mutant BA.1 and BA.2 strains were analyzed. Combined with the outside-well dilution mode of the strongly positive samples, the kit for high potency of SARS-CoV-2 IgG screening was determined. 【Results】 When the internal control reference B2 was used as the standard, the detection sensitivity of product A and B was 1∶32 vs 1∶8; the detection sensitivity of product A was 4 times that of product B. The correlation Pearson r between the results given by two kits was 0.944 1(P<0.000 1). Product B with low sensitivity was primarily selected as an alternative kit. The ELISA IgG results of samples from mixed plasma showed that the order of correlation r between product A and B was 0.988. The correlation r between product A and neutralization antibody potency of the three viruses was original strain (0.978)>BA.2(0.970)>BA.1(0.799); the order of correlation r between ELISA IgG results of product B and neutralization antibody potency of the three viruses was original strain(0.994)>BA.2(0.968)>BA.1(0.804). If twice-diluted B2 was taken as the excellent standard, 55.4% of product B met the criterion, while 47.2% of product A met.For positive plasma with high IgG potency, the product B kit required a lower dilution of the sample, which was more convenient to operate. 【Conclusion】 Both of the ELISA IgG kit from product A and B can be used to screen IgG antibodies of SARS-CoV-2, while product B is more suitable for screening positive plasma with high IgG potency.
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【Objective】 To determine the best collection time period of plasma which can be used for human COVID-19 immunoglobulin for intravenous injection through SARS-CoV-2-IgG change and neutralizing antibody distribution against different virus strain in representative mixed plasma before and after Omicron strain infection by ELISA and pseudovirus neutralization test. 【Methods】 An ELISA method for quantitative detection of SARS-CoV-2-IgG was established and its linear range,accuracy and precision was verified. SARS-CoV-2-IgG potency was detected in 25 convalescent plasma which were collected 20-40 days after confirmed Omicron infection, two groups of mixed plasma samples WP1 and WP2 were prepared according to the SARS-CoV-2-IgG results, and pseudovirus neutralization experiments with different virus strain (prototype strain, BA. 1,BA.2, BA.4/5, BF.7, BQ.1.1) were carried out to determine the distribution of neutralizing antibodies against different virus strain. SARS-CoV-2-IgG potency of representative mixed plasma collected from 14 plasma stations subordinate to the company before and after Omicron strain infection was detected, including Omicron convalescent plasma (OP) collected from different plasma stations from December 2022 to May 2023 and normal pool plasma (VN) feed in March 2023 which collected from March 2022 to December 2022. According to the results, the difference and the change rule with time of SARS-CoV-2-IgG before and after Omicron strain infection were analyzed. 【Results】 The linearity of SARS-CoV-2-IgG ranged from 6.25 to 200 EIU/mL, the accuracy in-batch ranged from 81.793% to 106.985%, the precision in-batch ranged from 1. 100% to 13.000%, and the total error in-batch ranged from 2.988% to 22.679%. The accuracy between batches ranged from 90.788%to 96.893%, the precision between batches ranged from 4.870% to 6.272%, and the total error between batches ranged from 9.192% to 15.399%. The results of pseudovirus neutralizing antibody showed that the potency of different virus strain neutralizing antibodies were in the order of prototype strain>BA.2>BA.4/5>BF.7≈ BQ.1.1>BA.1 and the correlation between WP1 and WP2 was high (Pearson r=0. 931 1, P=0.002 3) which indicated that the potency distribution of neutralizing antibodies of different virus strain in Omicron convalescent plasma was basically stable. Compared with the mixed convalescent plasma sample G128 collected in June 2022, the potency of Omicron neutralizing antibodies of WP series were significantly higher, the ratio of BA.2 antibody to prototype antibody increased from 26.9% (before infection) to 82.6%-87.5% (after infection). The results of VN series before Omicron infection were < 100 EIU/mL, and the results of OP series after Omicron infection showed that the plasma collected from the beginning of December 2022 was the peak of antibody in the same month,and then dropped sharply, entering a short plateau in February-March 2023 (potency was about 40% of the peak value),and then dropped sharply again in April (potency was about 20% of the peak value). 【Conclusion】 The potency and proportion of neutralizing antibody against Omicron subtype in convalescent plasma after COVID-19 Omicron strain infection increased significantly. IgG antibody of plasma donors in different regions reached its peak in the month of infection, then continued to dropped sharply. The best collection period of plasma that can be used for human COVID-19 immunoglobulin for intravenous injection was 1 to 2 months after infection.