Of depression and immunity: does sex matter?

It is firmly established that women experience major depression (MD) at roughly twice the rate of men. Contemporary research has indicated that sex hormones comprise crucial orchestrators of the differences in susceptibility associated to sex in MD, as well as in certain infectious and autoimmune diseases. Interestingly, it has been suggested that altered functioning of the immune system may be implicated in the medical morbidity of this affective disorder. To make matters more complicated, data accumulated largely during the last two decades advocate the innate inflammatory immune response as a mechanism that may contribute to the pathophysiology of MD, mainly through alterations in the ability of immune cells to secrete pro-inflammatory cytokines. Although the literature is limited, the bi-directional influences between the brain and the immune system appear to present sex-related motifs whose elucidation is far from being completely achieved but comprises a matter of intensive research. Herein, we provide a first critical glimpse into if and how sex differences in immunity may be implicated in the pathophysiology of MD. The review's major aim is to sensitize clinical scientists of different disciplines to the putative impact of immune sexual dimorphism on MD and to stimulate basic research in a need to delineate the neuroimmunological substrate in the appearance, course and outcome of this stress-related disorder.