When comparing μS−/−/Eμ-TCL1, Eμ-TCL1, and AID−/−/Eμ-TCL1 CLL cells freshly purified from the spleens of these mice, we found that although there was significant clonal variation between samples, AID-deficient CLL cells produced the most secretory IgM and XBP1s, while secretory IgM-deficient CLL cells produced the least XBP1s (Fig. 4H). The gene discussed is CD40LG; the disease is B-cell chronic lymphocytic leukemia.