Small intestinal submucosa induces loss of mitochondrial integrity and caspase-dependent apoptosis in human T cells

Porcine small intestinal submucosa (SIS) is a cell-free biomaterial used in humans for wound healing and as scaffold material for constructive remodeling of damaged or missing tissue. We have previously shown that SIS contains a factor that suppresses human helper T cell subset differentiation and expansion by inducing programmed cell death. Our aims here were to identify in detail the processes involved in SIS-induced T cell apoptosis and to perform the first characterization of the apoptosis-inducing factor present in SIS. In in vitro experiments, we utilized human T cell lines, Jurkat and CEM, to identify the processes involved in SIS-induced T cell apoptosis. Two types of sterile SIS material were used: hydrated sheets and rehydrated clinical-grade sheets. We found that SIS-mediated apoptosis as detected by induction of membrane annexin V staining involved the loss of mitochondrial membrane potential and was dependent on caspase activation. We eliminated transforming growth factor beta (TGF-beta), Fas ligand (FasL), and galectin family members as factors in SIS-mediated T cell apoptosis. We further established that processes required to prepare SIS for clinical use, freeze-drying, and gas sterilization destroyed the apoptosis-inducing factor. SIS contains a factor that induces loss of mitochondrial integrity and caspase-dependent apoptosis in human T cells. This factor is destroyed by freeze-drying and gas sterilization and is not TGF-beta, FasL, or a galectin family member. Normal T cell homeostasis in gut-associated tissues may be regulated in part by this unknown factor.