Temporal pattern of humoral immune response in mild cases of COVID-19

BACKGROUND Understanding the humoral response pattern of coronavirus disease 2019(COVID-19)is one of the essential factors to better characterize the immune memory of patients,which allows understanding the temporality of reinfection,provides answers about the efficacy and durability of protection against severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),and consequently helps in global public health and vaccination strategy.Among the patients who became infected with SARS-CoV-2,the majority who did not progress to death were those who developed the mild COVID-19,so understanding the pattern and temporality of the antibody response of these patients is certainly relevant.AIM To investigate the temporal pattern of humoral response of specific immunoglobulin G(IgG)in mild cases of COVID-19.METHODS Blood samples from 191 COVID-19 real-time reverse transcriptase-polymerase chain reaction(RT-qPCR)-positive volunteers from the municipality of Toledo/Paraná/Brazil,underwent two distinct serological tests,enzyme-linked immunosorbent assay,and detection of anti-nucleocapsid IgG.Blood samples and clinicoepidemiological data of the volunteers were collected between November 2020 and February 2021.All assays were performed in duplicate and the manufacturers'recommendations were strictly followed.The data were statistically analyzed using multiple logistic regression;the variables were selected by applying the P<0.05 criterion.RESULTS Serological tests to detect specific IgG were performed on serum samples from volunteers who were diagnosed as being positive by RT-qPCR for COVID-19 or had disease onset in the time interval from less than 1 mo to 7 mo.The time periods when the highest number of participants with detectable IgG was observed were 1,2 and 3 mo.It was observed that 9.42%of participants no longer had detectable IgG antibodies 1 mo only after being infected with SARS-CoV-2 and 1.57%were also IgG negative at less than 1 mo.At 5 mo,3.14%of volunteers were IgG negative,and at 6 or 7 mo,1 volunteer(0.52%)had no detectable IgG.During the period between diagnosis by RT-qPCR/symptoms onset and the date of collection for the study,no statistical significance was observed for any association analyzed.Moreover,considering the age category between 31 and 59 years as the exposed group,the P value was 0.11 for the category 31 to 59 years and 0.32 for the category 60 years or older,showing that in both age categories there was no association between the pair of variables analyzed.Regarding chronic disease,the exposure group consisted of the participants without any comorbidity,so the P value of 0.07 for the category of those with at least one chronic disease showed no association between the two variables.CONCLUSION A temporal pattern of IgG response was not observed,but it is suggested that immunological memory is weak and there is no association between IgG production and age or chronic disease in mild COVID-19.

Antibody-Like Phosphorylation Sites in Focus of Statistically Based Bilingual Approach

In accordance with previous reports, the sequences related to phosporylated protein segments occur in conserved variable domains of immunoglobulins including first of all certain N-terminally located segments. Consequently, we look here for the sequences 1) composing human and mouse proteins different from antigen receptors, 2) identical with or highly similar to nucleotide sequence representatives of conserved variable immunoglobulin segments and 3) identical with or closely related to phosphorylation sites. More precisely, we searched for the corresponding actual pairs of DNA and protein sequence segments using five-step bilingual approach employing among others a) different types of BLAST searches, b) two in-principle-different machine-learning methods predicting phosphorylated sites and c) two large databases recording existing phosphorylation sites. The approach identified seven existing phosphorylation sites and thirty-seven related human and mouse segments achieving limits for several predictions or phylogenic parameters. Mostly serines phosporylated with ataxia-telangiectasia-related kinase (involved in regulation of DNA-double-strand-break repair) were indicated or predicted in this study. Hypermutation motifs, located in effective positions of the selected sequence segments, occurred significantly less frequently in transcribed than non-transcribed DNA strands suggesting thus the incidence of mutation events. In addition, marked differences between the numbers and proportions of human and mouse cancer-related sequence items were found in different steps of selection process. The possible role of hypermutation changes within the selected segments and the observed structural relationships are discussed here with respect to DNA damage, carcinogenesis, cancer vaccination, ageing and evolution. Taken together, our data represent additional and sometimes perhaps complementary information to the existing databases of empirically proven phosphorylation sites or pathogenically important spots.