- Interleukin-21 receptor (IL-21R) is up-regulated by CD40 triggering and mediates proapoptotic signals in chronic lymphocytic leukemia B cells. de Totero, D., Meazza, R., Zupo, S., Cutrona, G., Matis, S., Colombo, M., Balleari, E., Pierri, I., Fabbi, M., Capaia, M., Azzarone, B., Gobbi, M., Ferrarini, M., Ferrini, S. Blood (2006)