Altered innate immunity following spinal cord injury

Study Design: Cross-sectional, paired cohort study. Objectives: To replicate the finding of impaired immunocyte function following spinal cord injury (SCI). To determine whether cellular immune function in SCI subjects with decentralized sympathetic nervous system (SNS) (T6 and above) varies from SCI subjects with intact SNS (below T6). Setting: University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, NJ, USA. Method: In vitro immune assays: (1) natural killer (NK) cell cytotoxicity using a K562 target cell line in a 4-h chromium(51) release assay. The mean of three samples for each effector-to-target (E: F) ratio (25: 1, 50: 1, 100: 1) was used in the analyses. (2) Cell enumeration was performed using commercially available antibodies and standard flow cytometry techniques. Results: Participation of 36 SCI subjects and 36 individually age- and sex- matched healthy controls. SCI subjects were stratified into two groups, that is, neurologic level of injury (NLI) at T6 or above (26 subjects) and NLI below T6 (10 subjects). No statistically significant differences were identified between NLI T6 and above and NLI below T6 groups for the NK cytotoxicity assay. There was a statistically significant reduction in NK cell numbers in all subjects with SCI as compared to their paired controls. There was a statistically significant reduction in NK cell cytotoxicity in SCI subjects, relative to the controls for E: F ratio of 100: 1 (F = 6.18, d. f. = 34, P = 0.02). Conclusion: We replicated the finding of decreased NK cell number and cytotoxicity in SCI subjects. The mechanism behind these findings needs to be further investigated, with the long-term goal of developing therapeutic strategies to improve immune function.