Furthermore, while under in vitro culture conditions FoBs showed only minimal PC differentiation upon T-independent stimulation, FoBs exhibited formation of IgM+ PCs with similar efficiency as MZBs in the in vivo adoptive transfer model, which likely is related to the observed transdifferentiation of FoBs to MZB-like cells in this system of lymphopenia-induced homeostatic proliferation. This evidence concerns the gene CD40LG and lymphopenia.