Expression of cytolytic protein–perforin in peripheral blood lymphocytes in severe traumatic brain injured patients

Abstract Purpose The purpose of this study was to investigate the changes of cytotoxic protein–perforin in peripheral blood lymphocytes in severe TBI patients and possible correlation between severity of TBI and perforin expression. Methods Flow cytometry was used for simultaneous detection of intracellular perforin and cell surface antigens of peripheral blood lymphocytes of 20 severe TBI patients on day 1, 4 and 7 after the onset of injury. Peripheral blood mononuclear cells from 20 healthy volunteers were used as control. Clinical and laboratory parameters were also recorded. Results There was a statistically significant decrease of perforin-positive lymphocytes including T, natural killer (NK) and NKT cells on day 4 as compared with day 1 after the brain injury or healthy controls. On day 7, perforin expression was restored in lymphocyte of cytotoxic phenotype (CD8 + T lymphocytes, NK cells, and NKT cells) compared with day 1. High positive correlation was found between the severity of TBI and frequency of perforin-positive cells on day 4 when the occurrence of the intra-hospital infections was the highest. Conclusion Severe TBI significantly decreases perforin expression in T lymphocytes, NK and NKT cells, which indicate a possible mechanism underlying the high susceptibility to infections.