Effect of transfusion of aged platelets on CD40L expression in lung tissue. Histologic sections of CD40L stained rat lungs at 20× magnification. (A) saline control; (B) LPS control; (C) saline plus fresh PLTs day 0; (D) LPS plus PLTs day 0; (E) saline plus aged PLTs (PLTs day 5); (F) LPS plus PLTs day 5. CD40L is indicated by brown staining. In all sections, except for the saline-negative control, CD40L staining is present on pulmonary T cells and on the endovascular wall (arrows).