[Objective] To determine the feasibility of preparing plasminogen (Pg) with Fraction Ⅲ precipitation (hereinafter referred to as FⅢ-P) from low-temperature ethanol process by full chromatography (hereinafter referred to as FⅢ-P process). [Methods] The FⅢ-P was diluted with dissolution buffer at different dilution times and stirring time. The potency and antigen concentration of Pg in dissolution sample were detected and the dissolution and clarification conditions were determined. Pre-treatment of loading sample and pre-experiment of affinity chromatography were carried out on the FⅢ-P dissolution sample to judge whether the loading sample had an impact on the chromatography by observing the performance of the affinity chromatography column and to evaluate whether the affinity chromatography could achieve the purpose of purifying Pg by detecting the plasma protein antigen concentration and Pg potency of the samples in the process. Two batches of FⅢ-P process were studied step by step, and the specific activity, steps and total recovery, and the output of Pg per ton of plasma were calculated. The feasibility of preparing Pg by FⅢ-P process was evaluated by comparing with the data of full chromatography process using plasma as raw material (hereinafter referred to as plasma process). [Results] The FⅢ-P was dissolved with 10 times of dissolution buffer, stirred for 1 hour, centrifuged at room temperature of 10 000×g for 15 minutes. The supernatant was first filtered with a screen, then clarified with an 8/0.8 μm filter, and finally filtered with a 0.45/0.2 μm filter and loaded. Pre-test showed that from clarification and filtration to Pg affinity chromatography, the step recovery of activity and antigen was 39.51% and 108.64%, respectively, the antigen concentration of Pg increased by 31.16 times and the activity increased by 11.39 times after affinity chromatography, which reaching the effect of affinity chromatography purification of Pg. The results of 2 batches of step-by-step scale-up FⅢ-P process showed that the total recoveries of antigen and activity from plasma to SP chromatography of FⅢ-P process were (45.76±1.10)% and (24.15±0.59)%, respectively, which had a total loss of about 1/3 of antigen and about 2/3 of activity compared to the plasma process. The Pg specific activity of SP chromatography eluent was (4.68±0.25) U/mg, which was about half of that of plasma process, but meeted the internal standard of > 4 U/mg. The output of Pg antigen per ton of plasma in the FⅢ-P process was 68.73% of that in the plasma process, and the output of Pg activity per ton of plasma in the plasma process was 29.82% of that in the plasma process, which basically achieved the purpose of waste utilization of FⅢ-P. [Conclusion] The technical route of preparing Pg from FⅢ-P by full chromatography is feasible.

【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.

【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.