Circulating lymphocyte subsets, natural killer cell cytotoxicity, and components of hypothalamic-pituitary-adrenal axis in Croatian war veterans with posttraumatic stress disorder: cross-sectional study

Aim

To determine peripheral blood lymphocyte subsets – T cells, helper T cells, cytotoxic T cells, B cells, and natural killer cells, natural killer cell cytotoxicity, serum cortisol concentration, and lymphocyte glucocorticoid receptor expression in Croatian combat veterans diagnosed with chronic posttraumatic stress disorder (PTSD); and to examine the relationship between the assessed parameters and the time passed since the traumatic experience.

Methods

Well-characterized group of 38 PTSD patients was compared to a group of 24 healthy civilians. Simultaneous determination of lymphocyte subsets and the expression of intracellular glucocorticoid receptor was performed using three-color flow cytometry. Natural killer cell cytotoxicity was measured by ⁵¹Cr-release assay and the serum cortisol concentration was determined by radioimmunoassay.

Results

We found higher lymphocyte counts in PTSD patients than in healthy controls (2294.7 ± 678.0/μL vs 1817.2 ± 637.0/μL, P = 0.007) and a positive correlation between lymphocyte glucocorticoid receptor expression and the number of years that passed from the traumatic experience (r_s = 0.43, P = 0.008). Lymphocyte glucocorticoid receptor expression positively correlated with serum cortisol concentration both in PTSD patients (r = 0.46, P = 0.006) and healthy controls (r = 0.46, P = 0.035).

Conclusion

This study confirmed that the immune system was affected in the course of chronic PTSD. Our findings also indicated that the hypothalamic-pituitary-adrenal axis profile in PTSD was associated with the duration of the disorder. Due to the lack of power, greater sample sizes are needed to confirm the results of this study.Prolonged or frequently repeated stress response during symptomatic episodes in chronic posttraumatic stress disorder (PTSD) can result in neuroendocrine and immune alterations, posing serious threat to mental and physical health (1,2). Evidence suggests that PTSD is related to increased medical morbidity, particularly from cardiovascular and autoimmune diseases (3). With controversial findings when neurobiology of PTSD is concerned, the patophysiological mechanisms underlying increased susceptibility to disease are not clear (4,5). However, it has been implicated that the sympathetic-adrenal-medullary (SAM) and the hypothalamic-pituitary-adrenal axes are the key mediators in this process (6,7).The immune system interacts with the hypothalamic-pituitary-adrenal axis in a bidirectional fashion to maintain homeostasis. Being the primary effector of the stress response, cortisol modifies the complex cytokine network and, consequently, leukocyte function and recirculation (8). These effects are achieved through its interaction with the specific intracellular glucocorticoid receptors (9).Studies of the leukocyte recirculation (10,11), immune cells function (12), and hypothalamic-pituitary-adrenal axis activity (5) in PTSD yielded controversial results. Overall findings support the hypothesis that immune activation in PTSD may be associated with Th2 cytokine shift and alterations in the proinflammatory cytokine system (4). Besides, it is believed that PTSD is linked with low plasma cortisol levels and higher glucocorticoid receptor expression, suggesting enhanced feedback sensitivity to cortisol (13). In contrast to these findings, Gotovac et al (14) showed that Croatian combat veterans with PTSD, approximately 6 years after traumatic event, had lower expression of glucocorticoid receptor in lymphocyte subsets, with higher serum cortisol concentration than healthy subjects. Majority of other studies did not take into account the time passed since the trauma and their samples mainly included Vietnam veterans (15) or Holocaust survivors (16), who had greater time gap since the traumatic experience than Croatian war veterans.Considering the strong discrepancies in the results published to date, we performed a cross-sectional study to evaluate the correlation between PTSD in Croatian combat war veterans and the percentages of circulating lymphocyte subsets, natural killer cell cytotoxicity as a measure of immune function, and the serum cortisol concentration with lymphocyte glucocorticoid receptor expression as components of hypothalamic-pituitary-adrenal axis. The emphasis was put on the relationship between the assessed parameters and the time passed since the traumatic experience.