Background 24The COVID-19 pandemic caused by SARS-CoV-2 coronavirus threatens global public 25 health. Currently, neutralizing antibodies (NAbs) versus this virus are expected to 26 correlate with recovery and protection of this disease. However, the characteristics of 27 these antibodies have not been well studied in association with the clinical 28 manifestations in patients. 30 Methods 31Plasma collected from 175 COVID-19 recovered patients with mild symptoms were 32 screened using a safe and sensitive pseudotyped-lentiviral-vector-based neutralization 33 assay. Spike-binding antibody in plasma were determined by ELISA using RBD, S1, 34 and S2 proteins of SARS-CoV-2. The levels and the time course of SARS-CoV-2-35 specific NAbs and the spike-binding antibodies were monitored at the same time. 36 37 Findings 38 SARS-CoV-2 NAbs were unable to cross-reactive with SARS-CoV virus. SARS-CoV-39 2-specific NAbs were detected in patients from day 10-15 after the onset of the disease 40 and remained thereafter. The titers of NAb among these patients correlated with the 41 spike-binding antibodies targeting S1, RBD, and S2 regions. The titers of NAbs were 42 variable in different patients. Elderly and middle-age patients had significantly higher 43 plasma NAb titers (P<0.0001) and spike-binding antibodies (P=0.0003) than young 44 patients. Notably, among these patients, there were ten patients whose NAb titers were 45 under the detectable level of our assay (ID50: < 40); while in contrast, two patients, 46 showed very high titers of NAb, with ID50 :15989 and 21567 respectively. The NAb 47 titers were positive correlated with plasma CRP levels but negative correlated with the 48 lymphocyte counts of patients at the time of admission, indicating an association 49 between humoral response and cellular immune response.50 51 Interpretation 52The variations of SARS-CoV-2 specific NAbs in recovered COVID-19 patients may 53 raise the concern about the role of NAbs on disease progression. The correlation of 54 NAb titers with age, lymphocyte counts, and blood CRP levels suggested that the 55 interplay between virus and host immune response in coronavirus infections should be 56 further explored for the development of effective vaccine against SARS-CoV-2 virus. 57 Furthermore, titration of NAb is helpful prior to the use of convalescent plasma for 58 prevention or treatment. Sciences 64 65 66 67 All rights reserved. No reuse allowed without permission.

In the Acknowledgements section of this Article, the grant number 'SQ2019FY010009' should have been '2019FY101500'; this has been corrected online.

In this communication we present the detailed disulfide structure of IgG2 molecules. The consensus structural model of human IgGs represents the hinge region positioned as a flexible linker connecting structurally isolated Fc and Fab domains. IgG2 molecules are organized differently from that model and exhibit multiple structural isoforms composed of (heavy chain-light chain-hinge) covalent complexes. We describe the precise connection of all the disulfide bridges and show that the IgG2 C H1 and C-terminal C L cysteine residues are either linked to each other or to the two upper hinge cysteine residues specific to the IgG2 subclass. A defined arrangement of these disulfide bridges is unique to each isoform. Mutation of a single cysteine residue in the hinge region eliminates these natural complexes. These results show that IgG2 structure is significantly different from the conventionally accepted immunoglobulin structural model and may help to explain some of the unique biological activity attributed only to this subclass.

Hydrophobic interaction chromatography (HIC) was used to separate populations of recombinant IgG2 antibody that were created as a result of prolonged incubation at 40 degrees C. Antibody was separated by HIC into three major and seven minor fractions. All but one fraction was composed of antibody with distinct chemical modifications that resulted from exposure to elevated temperature. The results of intact and reduced mass analysis as well as peptide map data derived from the three major HIC fractions indicated that the antibody was being chromatographically separated into populations containing a succinimidyl intermediate in complementarity determining region 1 (CDR1) on zero, one, and two light chain arms. Lower level species purified by HIC were analyzed by intact and reduced mass analysis and laser-induced fluorescence capillary electrophoresis (CE-LIF) and consisted of an antibody that was clipped in four different places in the heavy chain as well as misfolded and aggregated antibody. The potency of the recombinant antibody containing a succinimidyl intermediate on zero, one, and two light chain arms was analyzed by LANCE binding assay and a cell based in vitro bioassay, and the occurrence of this modification on one or both light chain arms was associated with a reduction in the binding affinity of the molecule to the target by approximately 10%. We show that HIC has the unique ability as a first step purification method to separate populations of antibody which are covalently modified under stability programs. The method conditions that have been developed for the HIC assay are ideal for purifying antibodies with labile modifications for the purpose of further characterization.

In order to investigate the effects of molybdenum (Mo) on sperm parameters and testicular oxidative stress, the ICR strain of adult mice were exposed to different doses of molybdenum for a sub-acute toxicity test. Compared to the control, our results showed that the sperm parameters, including the epididymis index, sperm motility, sperm count, and morphology, increased by a moderate dose of Mo (25 mg/L), but were negatively affected at high doses (≥ 100 mg/L). In addition, the changes of sperm parameters were accompanied with changes of the superoxide dismutase (SOD) activities, the glutathione peroxidase (GPx) activities, and the malondialdehyde (MDA) levels in testes. In conclusion, Mo affects the sperm quality through regulating the testicular oxidative stress in a complex manner.