Lack of affinity signature for germinal center cells that have initiated plasma cell differentiation (Figure2)

Long-lived plasma cells (PCs) secrete antibodies that can provide sustained immunity against infection. It has been proposed that high affinity cells are preferentially selected into this compartment, potentiating the immune response. We used single cell RNA-seq to track the germinal center (GC) development of Ighg2A10 cells, specific for the Plasmodium falciparum circumsporozoite protein (PfCSP). Following immunization with Plasmodium sporozoites we identified 3 populations of cells in the GC light zone. One population expressed a gene signature associated with the initiation of PC differentiation and had an enhanced propensity to form PCs in vitro. Unexpectedly, the estimated affinity of this putative pre-PC population was indistinguishable from cells in the GC generally. This was also true when high- or low-avidity recombinant PfCSP proteins were used as immunogens. Immunization with low-avidity PfCSP did, however, induce increased affinity maturation. Collectively these findings suggest that the initiation of PC development in the GC occurs via an affinity independent process. Overall design: Probe+ IgD- Ighg2A10 B cells stained with TotalSeq-C hashtag antibodies were isolated by Fluorescence-activated cell sorting (FACS) from recipient mice that had been immunized with irradiated sporozoites either 7 or 21 days prior. The transcriptome and VDJ sequences of sorted cells was then analyzed using scRNAseq.