Influence of neurological level on immune function following spinal cord injury: a review

Due to the high incidence of lifelong infections in persons with spinal cord injury (SCI), the authors examined level of injury-related immune characteristics in a cohort of subjects with chronic SCI. Since the sympathetic nervous system and the endocrine system are known to be modulators of immune function, one possible explanation for heightened incidence of infections includes dysregulation of sympathetic outflow tracts in individuals with tetraplegia or high paraplegia. Natural killer cell cytotoxicity (NKCC) and bactericidal function of circulating neutrophils were assayed in a group of 10 individuals with chronic complete cervical SCI, a group of 8 individuals with paraplegia with injuries below the main sympathetic outflow (T-10 and below) and a group of 18 age- and sex-matched controls. In addition, a psychiatric assessment of depression was performed as well as assays of pituitary and adrenal functions. Analyses revealed no significant differences in immune function between all subjects with SCI combined and their matched controls. Further analyses stratifying based on presence or absence of sympathetic dysregulation revealed significantly impaired phagocytic ability and a trend toward reduced NKCC in the group with tetraplegia compared with their controls. Hormonal assays showed that dehydroepiandrosterone (DHEA), and dehydroepiandrosterone sulfate (DS) were higher in individuals with tetraplegia than controls, but no such differences were observed in individuals with paraplegia compared with their controls. The results of this study suggest that individuals sustaining complete cervical SCI experience alterations in immune function, while those with lesions at or below T-10 do not. These findings of level of injury related immune alteration could not be explained by mood differences. This paper is a review of previously published work and the authors' current thinking regarding increased acquisition of infections in this population.