Analysis of proposed human B1 cells

The recent discovery of the human B1 cells, identified by the expression of CD20, CD27 and CD43 in absence of expression of CD70 and CD69 has been subject of debate. Some studies have raised the possibility that these cells are B cells differentiating towards the plasmablast and plasma cell stage rather than being the human counterpart of murine B1 cells. No further in depth studies have been performed. Therefore, a functional comparison was made between, the proposed B1 cells and plasmablasts. We observed that for several functional characteristics (distribution of isotypes of spontaneously producted antibodies, production of antigen-specific antibodies after vaccination with both T-cell dependent as well as T-cell independent antigen, the proposed B1 cells behaved similar to plasmablasts. In addition, we were able to differentiate the proposed B1 cells in vitro, indicating that they are not from a distinct lineage as the murine B1 cells. Gene expression analysis revealed that these cells cluster between memory B cells and plasmablasts, contradicting them being the genuine human counterpart of murine B1 cells, rather revealing a preplasmablast phenotype. Different B cells subsets were isolated from PBMC from healthy donors by a combination of magnetic and fluorescence activated cell sorting