Perforin affects regeneration in a mouse spinal cord injury model

Purpose of study: To study the role of the immune response in spinal cord injury, we previously investigated the effects of genetic deletion of functional T- and B-lymphocytes in recombination activating gene 2 (Rag2)-deficient mice. To dissect out another defined and more restricted component of the immune system, we now analyzed mice deficient in perforin, an enzyme with proteolytic activity expressed mainly by natural killer and cytotoxic lymphocytes. Materials and methods: Locomotor outcomes in perforin-deficient (Pfp-/-) mice and wild-type littermate controls were measured after severe compression injury of the lower thoracic spinal cord up to six weeks after injury. Results: According to both the Basso mouse scale score and single frame motion analysis, motor recovery of Pfp-/- mice was similar to wild-type controls. Interestingly, immunohistochemical analysis of cell types at six weeks after injury showed enhanced cholinergic reinnervation of spinal motor neurons caudal to the lesion site and neurofilament-positive structures at the injury site in Pfp-/- mice, whereas numbers of microglia/macrophages and astrocytes were decreased compared with controls. Conclusions: We conclude that, although, loss of perforin does not change the locomotor outcome after injury, it beneficially affects diverse cellular features, such as number of axons, cholinergic synapses, astrocytes and microglia/macrophages at or caudal to the lesion site. Perforin’s ability to contribute to Rag2’s influence on locomotion was observed in mice doubly deficient in perforin and Rag2 which recovered better than Rag2-/- or Pfp-/- mice, suggesting that natural killer cells can cooperate with T- and B-cells in spinal cord injury.