CD47Low Status on CD4 Effectors Is Necessary for the Contraction/Resolution of the Immune Response in Humans and Mice

How do effector CD4 T cells escape cell death during the contraction of the immune response (IR) remain largely unknown. CD47, through interactions with thrombospondin-1 (TSP-1) and SIRP-alpha, is implicated in cell death and phagocytosis of malignant cells. Here, we reported a reduction in SIRP-alpha-Fc binding to effector memory T cells (T-EM) and in vitro TCR-activated human CD4 T cells that was linked to TSP-1/CD47-induced cell death. The reduced SIRP-alpha-Fc binding (CD47(low) status) was not detected when CD4 T cells were stained with two anti-CD47 mAbs, which recognize distinct epitopes. In contrast, increased SIRP-alpha-Fc binding (CD47(high) status) marked central memory T cells (T-CM) as well as activated CD4 T cells exposed to IL-2, and correlated with resistance to TSP-1/CD47-mediated killing. Auto aggressive CD4 effectors, which accumulated in lymph nodes and at mucosal sites of patients with Crohn's disease, displayed a CD47(high) status despite a high level of TSP-1 release in colonic tissues. In mice, CD47 (CD47(low) status) was required on antigen (Ag)-specific CD4 effectors for the contraction of the IR in vivo, as significantly lower numbers of Ag-specific CD47(+/+) CD4 T cells were recovered when compared to Ag-specific CD47(-/-) CD4 T cells. In conclusion, we demonstrate that a transient change in the status of CD47, i.e. from CD47(high) to CD47(low), on CD4 effectors regulates the decision-making process that leads to CD47-mediated cell death and contraction of the IR while maintenance of a CD47(high) status on tissue-destructive CD4 effectors prevents the resolution of the inflammatory response.