Objective: To compare quality control (relative purity and specific activity) and process control [plasminogen (Pg) antigen recovery and potency recovery] indexes of samples before and after adding the Q chromatography step to the full chromatography process of human Pg, thereby determining whether the addition of this step could improve Pg recovery by affinity chromatography. Methods: A Q chromatography step was added before the Pg affinity chromatography in the original Pg chromatography process. The loading solution, flow through solution and eluate of Q chromatography and Pg affinity chromatography were collected. The potency of coagulation factor Ⅱ (FⅡ), Ⅶ (FⅦ), Ⅷ (FⅧ), Ⅸ (FⅨ), and Ⅹ(FⅩ) were detected by the coagulation method, the total protein content was detected by the BCA method, and the Pg potency was detected by the chromogenic substrate method. The content of specific plasma proteins was detected by immunoturbidimetry, the potency recovery of coagulation factors was calculated, and the flow direction of coagulation factors was analyzed. The recovery of different plasma protein antigens were calculated, and the distribution of impurity proteins was analyzed. The relative purity and specific activity of Pg, antigen content, and potency recovery in the target fractions were calculated and compared with the original process indicators, so as to determine the effect of adding Q chromatography on the original process. Furthermore, the reproducibility after process modification was assessed. Results: 100% of FⅡ, FⅩ, and FⅨ, 87.81% of FⅧ, and 40.44% of FⅦ in filtered plasma were removed by Q chromatography. The residual FⅦ (53.26%) and FⅧ (13.30%) in Q flow-through fraction were completely removed by Pg affinity chromatography. In both the original process (without Q-chromatography) and the modified process (with Q-chromatography), non-target plasma proteins mainly existed in the flow-through fraction of Pg affinity chromatography. The antigen recovery of IgM, ceruloplasmin (CER), and fibronectin (FNC) in Q-chromatography flow-through fraction were reduced. In contrast, antigen recovery of other plasma proteins [IgG, IgA, Pg, albumin (AlB), alpha-1-antitrypsin (AAT), and fibrinogen (Fg)] were all >90%, which were consistent with the protein composition and proportion in the original affinity chromatography loading solution. Compared with the recovery rate of Pg antigen in the original process (74.4%), the total recovery of Pg antigen in the modified process was significantly increased (89.97%). Compared with the recovery of IgG (97.48%) and Fg (95.32%) in the Pg affinity flows-through fraction of the original process, the modified process resulted in a slight reduction in the recovery of IgG (94.60%), while the recovery of Fg was not affected (95.05%). The potency recovery rate, specific activity, and relative purity of Pg after Q chromatography were 99.3%, 0.016 U/mg, and 0.15%. These values were the same as those of Pg affinity chromatography loading solution by the original process, indicating that introduction of Q chromatography did not affect subsequent Pg affinity chromatography. Compared with the recovery of Pg antigen in three batches of the original process (66.49±1.02)%, the recovery of Pg antigen in the affinity chromatography eluent of the modified process [five batches; (77.43±4.43)%] was significantly improved. Furthermore, the potency recovery was (86.80±4.28)%, the relative purity was (81.99±1.25)%, the specific activity was (8.679±1.073)U/mg, and the process was reproducible. Conclusion: The addition of Q chromatography could improve the recovery of Pg affinity chromatography in the full chromatography process.

【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.