Caspase-8 and cFLIP maintain B Cell populations and architecture 3766

Description Caspase-8 is a cysteine protease which, when activated, induces apoptosis and inhibits necroptosis. While previous studies have shown roles for Caspase-8 in B Cell development, survival, and function, these were performed before Caspase-8’s role in driving necroptotic cell death was appreciated. Thus, it is necessary to untether the functions of Caspase-8 in B Cells from the effects of necroptosis. Using mice lacking Caspase-8 and the necroptotic effector MLKL, we confirm previous reports of decreased splenic B Cell populations. We further identify deficits in B Cell development via deficits in late-stage Hardy Fractions in the bone marrow. We next use mice with a mutant of Caspase-8 which cannot oligomerize and additionally maintaine or ablate the Caspase-8 binding partner cFLIP. Here, we determine that decreases of both peripheral circulating B Cells as well as B Cell precursors in the bone marrow are dependent upon both Caspase-8 and cFLIP signaling. Finally, to remove the confounding variable of lymphoproliferation which occurs in DKO (Caspase-8-/-, MLKL-/-) mice, we performed bone marrow transplants in RAG recipients. We again saw decreased peripheral B Cells after one month, abnormal splenic architecture after 2 months, and a persisting decrease in early B Cell populations in the bone marrow 10 months later. Taken together, these data highlight a novel and persisting hematopoietic-intrinsic role of Caspase-8 and CFlip to maintain B Cell populations and architecture.