The major role of junctional diversity in the horse antibody repertoire.

The antibody repertoire (Rep-seq) sequencing revolutionized the diversity of antigen B cell receptor studies, allowing deep and quantitative analysis to decipher the role of adaptive immunity in health and disease. Particularly, horse (Equus caballus) polyclonal antibodies have been produced and used since the century XIX to treat and prophylaxis diphtheria, tuberculosis, tetanus, pneumonia, and, more recently, COVID-19. However, our knowledge about the horse B cell receptors repertories is minimal. We present a deep horse antibody heavy chain repertoire (IGH) characterization of non-infected horses using NGS (Next generation sequencing). This study obtained a mean of 248,169 unique IgM clones and 66,141 unique IgG clones from four domestic adult horses. Rarefaction analysis showed sequence coverage was between 52 % and 82 % in IgM and IgG isotypes. We observed that besides horses antibody can use all functional IGHV genes, around 80 % of their antibodies use only three IGHV gene segments, and around 55 % use only one IGHJ gene segment. This limited VJ diversity seems to be compensated by the junctional diversity of these antibodies. We observed that the junctional diversity in horse antibodies is widespread, present in more than 90 % of horse antibodies. Besides this, the length of this region seems to be higher in horse antibodies than in other species. N1 and N2 nucleotides addition range from 0 to 111 nucleotides. In addition, around 45 % of the antibody clones have more than ten nucleotides in both the N1 and N2 junction regions. This diversity mechanism may be one of the most important in providing variability to the equine antibody repertoire. This study provides new insights regarding horse antibody composition, diversity generation, and particularities compared to other species, such as the frequency and length of N nucleotide addition. This study also points out the urgent need to better characterize TdT in horses and other species to better understand antibody repertoire characteristics.

Shared B cell memory to coronaviruses and other pathogens varies in human age groups and tissues.

Vaccination and infection promote the formation, tissue distribution, and clonal evolution of B cells, which encode humoral immune memory. We evaluated pediatric and adult blood and deceased adult organ donor tissues to determine convergent antigen-specific antibody genes of similar sequences shared between individuals. B cell memory varied for different pathogens. Polysaccharide antigen-specific clones were not exclusive to the spleen. Adults had higher clone frequencies and greater class switching in lymphoid tissues than blood, while pediatric blood had abundant class-switched convergent clones. Consistent with reported serology, prepandemic children had class-switched convergent clones to severe acute respiratory syndrome coronavirus 2 with weak cross-reactivity to other coronaviruses, while adult blood or tissues showed few such clones. These results highlight the prominence of early childhood B cell clonal expansions and cross-reactivity for future responses to novel pathogens.

The N gene of SARS-CoV-2 was the main positive component in repositive samples from a cohort of COVID-19 patients in Wuhan, China.

BACKGROUND: Repositivity of SARS-CoV-2 nucleic acid in discharged COVID-19 patients was reported recently. However, the characteristics of repositive results are still not well understood, leading to a lack of effective monitoring strategies. METHODS: In the present study, a total of 59 COVID-19 patients were enrolled, and the characteristics of the repositive samples were analyzed. RESULTS: The repositive rate in this cohort was 15.79%. The N gene was the main target gene that was positive in the repositive results as well as in the last positive results of all patients. The median duration from diagnosis to the last positive test was 20 days (IQR, 16-31 days), and the longest duration was 40 days. Repositivity was only observed in IgM single- or both IgM- and IgG-positive patients, instead of IgG single-positive patients. CONCLUSIONS: There was a significant proportion of repositives in the recovered COVID-19 patients, and increasing the required number of negatives for consecutive nucleic acid tests may reduce the incidence of repositives. The recommended monitoring strategy for repositivity is monitoring the N gene in IgM-positive patients. This can ensure high sensitivity while reducing the time and cost of nucleic acid detection.