Modulation of the BCL-2 Family Blocks Sepsis-Induced Depletion of Dendritic Cells and Macrophages

This study examined the fate of dendritic cells (DCs) and macrophages (M Phi) in vivo in a murine model of sepsis. Wild-type, knockout, and transgenic mice were used to examine the role of Bcl-2 family members on the regulation of splenic DCs and M Phi survival. Bim knockout (Bim) mice and mice overexpressing Bcl-2 in selected hematopoietic cells were used: (a) overexpression of Bcl-2 in all hematopoietic cells using a vav promoter (Vav-Bcl-2) and (b) overexpression of Bcl-2 in all Major histocompatibility complex (MHC) class I cells (H-2K-Bcl-2). Mice underwent sham surgery or cecal ligation and puncture, and absolute numbers of splenic DCs and M Phi were determined. Importantly, two distinct M Phi populations, that is, well-differentiated "mature" M Phi population and a less differentiated "immature," "monocyte-like" (IM Phi) population were identified that demonstrated differential susceptibility to apoptosis. In wild-type mice, sepsis induced a 64% +/- 7% and a 77% +/- 3% decrease in absolute cell numbers of splenic DCs and IM Phi, respectively (n = 7, P < 0.05). Mature M Phi were not depleted in sepsis. No significant cell depletion was evident in Vav-Bcl-2, H-2K-Bcl-2, or Bim mice. We conclude that sepsis induces a major depletion of developing M Phi as well as DCs, and this depletion may be an important mechanism of immune suppression in sepsis.