[Depression, myocardial infarction and the immune system--the chicken before the egg problem].

Major depression is a risk factor, associated with a twofold increase in the incidence of ischemic heart disease (IHD). One of every 6 patients suffers from major depression following acute myocardial infarction (AMI). This connection is of major concern, considering that major depression is an independent risk factor for cardiac morbidity and mortality after AMI, increasing overall mortality fourfold. Activation of the immune system has a significant role in the pathogenesis of IHD and depression. Vast physiological responses, mediated mostly by activation of the immune system, accompany post MI depression and may account for increased prevalence of arrhythmias and high mortality. This includes activation of the hypothalamic-pituitary-adrenocortical axis, endothelial dysfunction, platelets activation and alterations of phospholipid composition in cell membranes. On the other hand, activation of the immune system after AMI includes elevated levels of interleukin-1 and interleukin-6. which induce "sickness behavior", characterized by symptoms similar to those observed in major depression. The key question raised by this data, whether inflammation is the common ground for both AMI and depression, or if it is accompanying one and sets the ground for the other, remains unanswered at this time. The significance of major depression as an independent risk factor for post MI mortality and morbidity raises the practical question, whether treatment of depression can reduce mortality after AMI. Several recent studies that evaluated this presumption, failed to prove it. In this review we present an overview of the cross interaction between depression, AMI and inflammation and its diagnostic and therapeutic implications.