CDB15:0000285 CD40LG — ITGAM

ABSTRACT: In addition to its classical CD40 receptor, CD154 also binds to αIIbβ3, α5β1, and αMβ2 integrins. Binding of CD154 to these receptors seems to play a key role in the pathogenic processes of chronic inflammation. This investigation was aimed at analyzing the functional interaction of CD154 with CD40, αIIbβ3, and α5β1 receptors. We found that the binding affinity of CD154 for αIIbβ3 is ∼4-fold higher than for α5β1. We also describe the generation of sCD154 mutants that lost their ability to bind CD40 or αIIbβ3 and show that CD154 residues involved in its binding to CD40 or αIIbβ3 are distinct from those implicated in its interaction to α5β1, suggesting that sCD154 may bind simultaneously to different receptors. Indeed, sCD154 can bind simultaneously to CD40 and α5β1 and biologically activate human monocytic U937 cells expressing both receptors. The simultaneous engagement of CD40 and α5β1 activates the mitogen-activated protein kinases, p38, and extracellular signal-related kinases 1/2 and synergizes in the release of inflammatory mediators MMP-2 and -9, suggesting a cross-talk between these receptors.

ABSTRACT: Antagonism of the CD154/CD40 pathway is a highly effective means of inducing long-term graft survival in preclinical models. Using a fully allogeneic murine transplant model, we found that CD154 blockade was more effective in prolonging graft survival than was CD40 blockade, raising the possibility that CD154 binds a second receptor. To test this, we queried the impact of CD154 antagonism in the absence of CD40. Data indicated that anti-CD154 functioned to reduce graft-infiltrating CD8+ T cells in both WT and CD40-/- hosts. Because it has recently been reported that CD154 can ligate CD11b, we addressed the impact of blocking CD154-CD11b interactions during transplantation. We utilized a specific peptide antagonist that prevents CD154 binding of CD11b but has no effect on CD154-CD40 interactions. CD154:CD11b antagonism significantly increased the efficacy of anti-CD40 in prolonging allograft survival as compared to anti-CD40 plus control peptide. Mechanistically, CD154:CD11b antagonism functioned to reduce the frequency of graft-infiltrating CD8+ T cells and innate immune cells. These data therefore demonstrate that blocking CD154 interactions with both CD40 and CD11b is required for optimal inhibition of alloimmunity and provide an explanation for why CD40 blockers may be less efficacious than anti-CD154 reagents for the inhibition of allograft rejection.