CD40L expression by CD4 but not CD8 T cells regulates antiviral immune responses in acute LCMV infection in mice.

CD40-CD40 ligand (CD40L) signaling plays multiple indispensable roles in cellular and humoral immunity. Impaired memory T-cell responses in the absence of CD40L have been well documented, but the requirement of this interaction for efficient priming of CD8 T cells especially under inflammatory conditions has been under debate. In contrast to previous publications, we report here that virus-specific CD8 T-cell responses as well as viral clearance are affected not only in the memory but also in the effector phase in CD40L mice infected with lymphocytic choriomeningitis virus (LCMV) Armstrong strain.

IL-12-mediated STAT4 signaling and TCR signal strength cooperate in the induction of CD40L in human and mouse CD8+ T cells.

CD40L is one of the key molecules bridging the activation of specific T cells and the maturation of professional and nonprofessional antigen-presenting cells including B cells. CD4(+) T cells have been regarded as the major T-cell subset that expresses CD40L upon cognate activation; however, we demonstrate here that a putative CD8(+) helper T-cell subset expressing CD40L is induced in human and murine CD8(+) T cells in vitro and in mice immunized with antigen-pulsed dendritic cells. IL-12 and STAT4-mediated signaling was the major instructive cytokine signal boosting the ability of CD8(+) T cells to express CD40L both in vitro and in vivo.