CD40LG and infection: To further evaluate whether an increase of IgT+ B-cells in the olfactory organ of survivor fish that survived 75 days after first infection was derived from the process of local IgT+ B-cell proliferation or from influx of B cells from systemic lymphoid organs, we performed in vivo proliferation studies of IgT+ B-cells and IgM+ B-cells stained with EdU, which can incorporate into DNA during cell division [26].