Cutting edge: Human B cell function is regulated by interaction with soluble CD14: Opposite effects on IgG1 and IgE production

The mechanism(s) controlling activation of naive B cells, their proliferati on, Ag receptor affinity maturation, isotype switching, and their fate as m emory or plasma cells is not fully elucidated. Here we show that between 24 and 60% of CD19(+) cells in PBMC bind soluble CD14 (sCD14), Tonsillar B ce lls also bind sCD14, but preferentially the CD38(-ve/low) cells. Interactio n of sCD14 with B cells resulted in higher levels of IgG1 and marked inhibi tion of IgE production by activated tonsillar B cells and Ag-stimulated PBM C. We found that sCD14 interfered with CD40 signaling in B cells, inhibited IL-6 production by activated B cells, and increased the kinetics and magni tude of CD40 ligand expression on T cells. Together with the previously rep orted effects on T cells, these findings define sCD14 as a novel soluble re gulatory factor capable of modulating cellular and humoral immune responses by interacting directly with T and B cells.