Role of IL-12 in overcoming the low responsiveness of NK cells to missing self after traumatic brain injury

- TBI induces a decreased expression of HLA class II on blood monocytes.
- TBI is associated with a decreased expression of HLA class I on blood monocytes.
- A mature phenotype and a low responsiveness of NK cells to missing self is observed.
- IL-12 is able to restore functions of NK cells after TBI.

Blood samples from 32 patients with severe Traumatic brain injury (TBI) were studied and compared with 11 cardiac surgery patients, and 29 healthy controls. A dramatic decreased expression of HLA class I molecules on monocytes was associated with increased KIR + NK cell frequency in TBI patients. Overall, the phenotype of TBI NK cells marked by KIR and CD57 expression and lower level of NKp46 and DNAM-1 reflected a differentiated state. The NK-cell response to missing self was marked by lower degranulation and lower IFN-γ production after stimulation with HLA class I deficient cell line. In contrast, the NK-cell ADCC was not altered. IL-12 was able to restore both IFN-γ production and the cytotoxicity capacities of NK cells. This study provides the first extensive description of the phenotype and functions of NK cells in TBI patients. Further evaluation of IL-12 treatment to overcome immunosuppression-induced nosocomial infections is warranted.