Unveiling distinct neuroimmune responses in mouse models of cervical spinal cord injury: Hemisection versus...

Traumatic cervical spinal cord injury (cSCI) causes severe neurological deficits and long-term disability. Preclinical models such as cervical vertebrate level 2 (C2) hemisection (C2HS), which disrupts communication between respiratory centers and the phrenic motoneurons pool, have been used for decades to study respiratory dysfunction and neuroinflammation after cSCI. Recently, contusive injuries such as cervical vertebrate level 3 hemicontusion (C3HC) have been increasingly employed, as they induce phrenic motoneuron damage and offer a more clinically relevant model of SCI. However, these two different models may engage distinct pathophysiological cascades, raising concerns about the generalizability of findings across injury paradigms. In this study, we compared neuroimmune responses following C2HS or C3HC in mice. Animals underwent either lesion, and spinal cord segments (C1-C8) were collected seven days post-injury for immuno-histological analyses around the lesion level and flow cytometry analyses at the lesion level. We observed that C2HS preserved more neurons accompanied by an upregulation of CD86 and F4/80 in macroglia, markers of activated macrophages, suggesting a response oriented toward phagocytic and reparative functions. This phenotype was associated with limited pro-inflammatory cell infiltration and normalized level of systemic IL-6 level. Conversely, C3HC induced more extensive tissue damage, heightened microglial activation, a trend toward increased astrocytic reactivity, and significantly elevated CSPG levels on the contralateral side. Moreover, a persistent NK cell, neutrophil, and CD43⁺ infiltrating cells, along with sustained elevation of circulating IL-6 These findings demonstrate distinct neuroinflammatory signatures and repairing mechanisms between models. This study underscores, for the first time, how injury type shapes neuroimmune mechanisms, reinforcing the need for lesion-specific therapeutic strategies in cervical spinal cord injury.