The ability of B-1 cells to become positively selected into the mature B cell pool, despite being  weakly self-reactive, has puzzled the field since its initial discovery. Here, we explore changes  in B cell positive selection as a function of developmental time by exploiting a link between  CD5 surface levels and the natural occurrence of self-reactive B cell receptors (BCRs) in BCR  wildtype mice. We show that the heterochronic RNA-binding protein Lin28b potentiates a  neonatal mode of B cell selection characterized by enhanced overall positive selection and the  developmental progression of CD5+ immature B cells in particular. Importantly, Lin28b  achieves this through amplifying the CD19/PI3K/c-Myc positive feedback loop and ectopic  Lin28b expression restores both positive selection and mature B cell numbers in CD19/ adult  mice. Thus, the temporally restricted expression of Lin28b alters the rules for B cell selection  during ontogeny through modulating tonic signaling. We propose that this neonatal mode of B  cell selection represents a cell intrinsic cue to accelerate the de novo establishment of the  adaptive immune system and incorporate a layer of natural antibody mediated immunity  throughout life. SOURCE: Jonas Ungerback (jonas.ungerback@med.lu.se) - Mikael Sigvardsson Lund University

Pluto Bioinformatics

GSE135603: Lin28b controls a neonatal to adult switch in B cell positive selection