CD4 and infection: A variety of immuno-suppressive mechanisms have been proposed to explain the link between allogeneic transfusion and postoperative infection, including decreased CD4 and interleukin 2 (IL-2) receptor-positive helper cells, increased CD8 suppresser cells, decreased natural killer cells, increased numbers of B cells, decreased IL-2 production, and increased prostaglandin E2 production [2, 6, 17].