Depression-Associated Cellular Components of the Innate and Adaptive Immune System

Abstract Major depressive disorder (MDD) is a serious and debilitating mood disorder that affects millions of people each year worldwide. A convergence of evidence has indicated that patients with MDD exhibit altered immune responsivity. The cytokine hypothesis of depression proposed in the 1990s is based on numerous studies showing elevated circulating proinflammatory cytokine levels and impaired cellular immunity in patients with MDD and in animal models of depression. In this section, we highlight aspects of innate and adaptive immunity that have been implicated in the pathophysiology of MDD and depression-associated behavior. We further discuss the significance of key immune cell types that lie at the interface between innate to adaptive immunity in the context of MDD. Finally, we introduce T-helper cell subsets of the adaptive immune responses, while their specific role in depression will be discussed in greater detail in a separate chapter.