- Costimulation via OX40L expressed by B cells is sufficient to determine the extent of primary CD4 cell expansion and Th2 cytokine secretion in vivo. Linton, P.J., Bautista, B., Biederman, E., Bradley, E.S., Harbertson, J., Kondrack, R.M., Padrick, R.C., Bradley, L.M. J. Exp. Med. (2003)