An unconventional VH1-2 antibody tolerates escape mutations and shows an antigenic hotspot on SARS-CoV-2 spike.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein continues to evolve antigenically, impacting antibody immunity. D1F6, an affinity-matured non-stereotypic VH1-2 antibody isolated from a patient infected with the SARS-CoV-2 ancestral strain, effectively neutralizes most Omicron variants tested, including XBB.1.5. We identify that D1F6 in the immunoglobulin G (IgG) form is able to overcome the effect of most Omicron mutations through its avidity-enhanced multivalent S-trimer binding. Cryo-electron microscopy (cryo-EM) and biochemical analyses show that three simultaneous epitope mutations are generally needed to substantially disrupt the multivalent S-trimer binding by D1F6 IgG. Antigenic mutations at spike positions 346, 444, and 445, which appeared in the latest variants, have little effect on D1F6 binding individually. However, these mutations are able to act synergistically with earlier Omicron mutations to impair neutralization by affecting the interaction between D1F6 IgG and the S-trimer. These results provide insight into the mechanism by which accumulated antigenic mutations facilitate evasion of affinity-matured antibodies.

Investigation of Antibody Levels During Three Doses of Sinopharm/BBIBP Vaccine Inoculation.

Levels of neutralizing antibodies (NAb) after vaccine against coronavirus disease 2019 (COVID-19) can be detected using a variety of methods. A critical challenge is how to apply simple and accurate methods to assess vaccine effect. In a population inoculated with three doses of the inactivated Sinopharm/BBIBP vaccine, we assessed the performance of chemiluminescent immunoassay (CLIA) in its implementation to detect severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) specific antibodies, as well as the antibody kinetics of healthcare workers throughout the course of vaccination. The antibody levels of NAb, the receptor-binding-domain (RBD) antibodies and IgG peaked one month after the second and remained at a relatively high level for over three months after the booster injection, while IgM and IgA levels remained consistently low throughout the course of vaccination. The production of high-level neutralizing antibodies is more likely when the inoculation interval between the first two doses is within the range of one to two months, and that between the first and booster dose is within 230 days. CLIA showed excellent consistency and correlation between NAb, RBD, and IgG antibodies with the cytopathic effect (CPE) conventional virus neutralization test (VNT). Receiver operating characteristic (ROC) analysis revealed that the optimal cut-off levels of NAb, RBD and IgG were 61.77 AU/ml, 37.86 AU/ml and 4.64 AU/ml, with sensitivity of 0.833, 0.796 and 0.944, and specificity of 0.768, 0.750 and 0.625, respectively, which can be utilized as reliable indicators of COVID-19 vaccination immunity detection.

Broad and durable antibody response after vaccination with inactivated SARS-CoV-2 in individuals with a history of 2003 SARS-CoV infection.

In vaccinees who were infected with SARS-CoV in 2003, we observed greater antibody responses against spike and nucleoprotein of both SARS-CoV-2 and SARS-CoV after a single dosage of inactivated SARS-CoV-2 vaccine. After receiving the second vaccination, antibodies against RBD of SARS-CoV-2 Wuhan, Beta, Delta, and recently emerged Omicron are significantly higher in SARS-CoV experienced vaccinees than in SARS-CoV naïve vaccinees. Neutralizing activities measured by authentic viruses and pseudoviruses of SARS-CoV, SARS-CoV-2 Wuhan, Beta, and Delta are greater in SARS-CoV experienced vaccinees. In contrast, only weak neutralizing activities against SARS-CoV-2 and variants were detected in SARS-CoV naïve vaccinees. By 6 months after the second vaccination, neutralizing activities were maintained at a relatively higher level in SARS-CoV experienced vaccinees but were undetectable in SARS-CoV naïve vaccinees. These findings suggested a great possibility of developing a universal vaccine by heterologous vaccination using spike antigens from different SARS-related coronaviruses.

Differential anthocyanin accumulation in radish taproot: importance of RsMYB1 gene structure.

KEY MESSAGE: RsMYB1a was the crucial MYB, and RsbHLH4 is the essential partner in regulating the anthocyanin biosynthesis in radish. There are four color types of radish according to whether or not the anthocyanin accumulates in the skin and flesh of taproot. Red radishes accumulate a substantial amount of anthocyanins in both the skin and flesh. It is well known that the MYB-bHLH-WD40 transcription factor(s) complex regulates the biosynthesis of anthocyanin in plants. Here in, four candidate MYB and bHLH genes, RsMYB1a, RsMYB1b, RsbHLH2 and RsbHLH4, were isolated from red radish 'Hongxin 1'. The expression of RsbHLH4 and the two structural genes RsANS and RsUFGT was significantly positively correlated with anthocyanin contents. The expression of RsMYB1a was also highly correlated with anthocyanin accumulation, particularly when the white flesh sample of 'Hongxin 1-1' was excluded. The transient expression of RsMYB1a in the radish cotyledon and leaf induced anthocyanin accumulation with even stronger promoting role when expression in combination with RsbHLH4. These results suggested that RsMYB1a was the crucial MYB, and that RsbHLH4 is an essential partner in regulating the biosynthesis of anthocyanins in radish. The low or undetectable RsbHLH4 expression paralleled the lack of anthocyanin accumulation in the white flesh of 'Hongxin 1-1' and 'Shaguan 1'. Assays demonstrated that RsMYB1a interacted with RsbHLH4 and activated the expression of RsbHLH4. Notably, all the dark red radish cultivars have a longer RsMYB1a genomic DNA sequence, while the short and nonfunctional RsMYB1a is present in non-red cultivars. The length of the first intron and the presence of an early stop codon of RsMYB1 might underlie the differential anthocyanin accumulation in the radish taproot.