Interleukin-6 and Lung Inflammation: Evidences of A Causing Role in Inducing Respiratory System Resistance Increments

Interleukin-6 has been shown to be increased in various pathological conditions involving the lungs, both experimentally induced in animals, or spontaneously occurring in humans. Experimental data demonstrating a significant role of interleukin-6 in commonly occurring respiratory system inflammatory diseases are reviewed. These diseases, i.e. asthma and chronic obstructive pulmonary disease, are characterised by respiratory system mechanical derangement, most of all because increased elastance and airway resistance. Recent findings showing a causative role of interleukin-6 in determining an airway resistance increment are reviewed. By applying the end-inflation occlusion method to study respiratory system mechanical properties before and after interleukin-6 administration, it was shown that this cytokine induced significant increments in both the resistive pressure dissipation due to frictional forces opposing the airflow in the airway (ohmic resistance), and in the additional resistive pressure dissipation due to the visco-elastic properties of the system, i.e. stress relaxation (visco-elastic resistance). A dose-dependent effect was also demonstrated. No effects were instead detected on respiratory system elastance. Even solely administrated in healthy mammals, interleukin-6 exhibits a significant effect on respiratory system resistances, leading to increased inspiratory muscle mechanical work of breathing. Thus, IL-6 may play an active role in the pathogenesis of respiratory system diseases. The possible involved mechanisms are discussed.