scRNA-seq revealed the special IG H&L V(D)J allelic inclusion rearrangement and the high proportion dual BCR expressing B cells

Since the first report of V (D) J " allelic exclusion/inclusion"and" dual BCR "in 1961, despite continuous new discoveries, the proportion and source mechanism of dual BCR under physiological conditions have been puzzling immuologists. This study takes advantage of the single cell V (D) J sequencing technology, which can perfectly match the heavy and light chains of BCR at the level of a single B cell, and obtain the full length mRNA sequence of the CDR3 region. By analyzing the pairing of functional IGH and IGL chains in single B cell from human and mouse bone marrow and peripheral blood, it was found that dual BCR B cells exhibit stable and high levels of expression. Among them, human bone marrow and peripheral blood contain about 10% dual (or multiple) BCR B cells, and mouse peripheral blood and bone marrow memory B cells contain about 20% dual (or multiple) BCR B cells. At the same time, we innovatively found that in each research sample of humans and mice, there are three (or more) functional rearrangements (mRNA level) of a single chain in a single B cell. By analyzing the position, direction and other compositional characteristics of the V(D)J gene family, we found that at least two(or more) of them are derived from over two(or more) specific allelic inclusion rearrangements of a single chromosome. (mRNA molecular level evidence). The results of this article provides new insights, new methods and modeling references for evaluating the proportion, molecular characteristics and source mechanisms of dual BCR B cells, as well as potential significance of allelic inclusion (exclusion escape) of V(D)J rearrangement.