Introduction
The circadian rhythm is characterized by biological oscillations occurring into a period of 24 hours, being responsible for a normal functioning of all organic systems, which may be influenced by variations in the light, temperature, sleeping timing and quality and different types of stress1 Shiftwork scale is characterized by working time outside the standard hours of 7:00 am to 6:00 pm and it is believed to negatively affects circadian rhythm, resulting in impairment of different organs and physiological systems2.
In this way, is widely accepted that alterations in the circadian rhythm can negatively affects the immune system3,4 endocrine and metabolic response5, cardiovascular response5 and also the pulmonary response6. Specifically, on the immune-regulated pulmonary response, it has been demonstrated that circadian rhythm drives bronchoconstriction/bronchodilatation, airway resistance, respiratory symptoms, which in summary may leads to exacerbation of respiratory diseases, particularly to chronic respiratory diseases, such as asthma4 and chronic obstructive pulmonary disease (COPD)7. However, concerning the immune-regulated pulmonary response, the effects of altered circadian rhythm on pulmonary cytokines, has been never investigated.
In fact, the alterations of circadian rhythm may lead to dysfunction of pulmonary but certainly of the systemic immune response3,4,6. In this context, it has been demonstrated that human monocytes obtained from individuals during the night, specifically during the sleep timing, release increased amounts of IL-12 (a pro-inflammatory cytokine) in response to endotoxin stimulation, while monocytes obtained during the day, responded to increased release of IL-10 (a immunoregulatory and anti-inflammatory cytokine)8. In the same way, establishing a causal nexus, some studies have demonstrated that the frequency and severity of exacerbations of COPD and asthma are increased specially during the night and in the early hours of the morning, which are hallmarks of the interference of circadian rhythm4,7. However, concerning the key role of humoral response, measured by analysis of cytokines, at the moment, no study has evaluated the possible alterations in the cytokine’s levels in the lungs in response to chronic stress.
Thus, the present study investigated for the first time the effects of chronic alteration of circadian rhythm in shiftwork scale policemen compared to civil men working in a diurnal constant scale, on the pulmonary immune response and function, as well as on the cellular and humoral systemic immune response.