Chronic Mental Stress Induces Reversible Reduction of Natural Killer Cells and CD56^dim Subpopulation

Generally, studying to be a health care provider is a stressful and demanding field and the students have to face many stressors that may affect their general health status including the immune system. This work aimed at studying the effect of prolonged naturalistic life-stress exposure on the percentage of peripheral blood T-lymphocytes and Natural Killer (NK) cells in female laboratory medicine students. 52 peripheral blood samples in the last week of the final written exam (stress time point) and 27 samples after 12 weeks rest (control) were withdrawn and analyzed by flow cytometry. At the stress time point, there was a significant high T helper cells percentage with elevation of T helper/T cytotoxic ratio, P value <0.001. Also, significant low percentages of NK cells and CD56^dim  together with high CD56^bright subpopoulations were detected, P value <0.001. Lymphocyte analysis of the subgroup that had an attach of common cold (34.6%) revealed significant reduction in the number of T cytotoxic and NK cells, P values 0.042 and 0.001 respectively. This study concluded that in humans, naturalistic chronic stress as expressed in academic exams has the potential to negatively affect the immune system, but normality is regained after sufficient stress relieve measures. Replication in larger and more diverse sample populations with inclusion of males for comparison is required, Also assessments of NK cell cytotoxicity and T helper cell subsets especially T regulatory cells are required for future studies.