IL-6 and APRIL in concert with CD138 expression promote ASC survival. (A-E) Purified transgenic B cells from WT and sdc1^−/− mice were injected into host mice in which the hematopoietic cells were either WT, IL-6 deficient (IL-6^−/−), or APRIL deficient (APRIL^−/−), and immunized and examined for YFP⁺ ASCs on day 7. (A) Graph depicts the percentage of WT and sdc1^−/− ASCs from the LN in the different host mice. (B) WT ASCs were examined for apoptosis by Annexin V staining. Representative contour plots are shown (left). Graph depicts percentage of apoptosis in the CD138⁺ compartment of WT ASCs in WT, IL-6^−/−, or APRIL^−/− hosts. (C) As in Figure 3H, intravital two-photon microscopy was performed on the surgically exposed popliteal LNs of immunized mice. Apoptotic events were recorded and quantified in a blinded manner. Graph represents the number of apoptotic events observed per hour. (D-E) WT and sdc1^−/− ASCs from the LN in the different host mice were examined for intracellular expression of Bcl-2 (D) and Mcl-1 (E). Graphs depict the MFI. *P < .05; **P < .01. ns, not significant.