Introduction: Platelets express a number of immunologically important proteins including CD40, and when activated, CD154 (CD40L), CD62P (P-selectin) and its ligand, (PSGL-1) which together link platelets to innate immunity. While previous studies have demonstrated a role for CD62P in ischemia/reperfusion (I/R) injury, no studies have determined a central role for platelets and platelet CD154 or CD40. We hypothesize that expression of CD154 on activated platelet mediate local mesenteric and remote lung tissue damage after ischemia and reperfusion.

Methods: Wild type (WT; C57BL/6J), CD40 knock out (KO) mice, CD154KO mice, CD154KO mice passively transferred with normal gamma globulin and platelet-depleted WT mice transfused with CD154KO platelets underwent mesenteric ischemia for 30 minutes and reperfusion for 3 hours. Local intestinal and remote lung injury was evaluated by histology.

Results: Wild type mice that underwent mesenteric I/R injury had tissue damage characterized by loss of villi integrity and hemorrhage. Remote lung injury was characterized by increased vascular congestion consisting of erythrocytes, platelets, neutrophils and monocytes. In contrast, CD40KO and CD154KO mice that underwent I/R demonstrated significantly less villi damage and no remote injury to the lung when compared to WT mice. The CD154KO mouse is the equivalent to human hypergammaglobulinemia which is characterized by the presence of normal to high serum IgM and the absence of other Ig isotypes. CD154KO mice passively transferred with normal IgG underwent I/R. Replacement of IgG in these mice did not induce local nor remote tissue damage. We next determined whether platelet-depleted WT mice transfused with CD154KO platelets presented with local and remote tissue damage following I/R. Mesenteric tissue damage in WT mice transfused with CD154KO platelets was similar when compared to WT mice. In contrast, no remote lung tissue injury was apparent when compared to WT mice by histological examination.

Conclusions: These findings indicate that CD154 expression on platelets does not mediate local (intestinal) injury. In contrast,, platelet CD154 expression is a critical mediator in remote (lung) tissue injury. Replacement of IgG in CD154KO mice did not mediate either local or remote tissue injury suggesting that CD154 on immune cells other than platelets participate in this injury process. Together, these findings suggest that multiple mechanisms are involved in local and remote tissue injury and also identify platelets or platelet CD154 as a potential therapeutic target to limit remote tissue injury.