Immune System Function and its Relation to Depression

Using data of 2,057 participants in the Dutch Lifelines database we explore the relationship between innate immune system response and acute (depressed for 2 weeks) or chronic (depressed for 2 years) depression in people. We then explore how riding a bicycle, a popular sport and mode of transport in the Netherlands, moderates this relationship. Focusing on acute depression, we found it associated with higher eosinophil, neutrophil and basophilic granulocyte cell counts but not with monocyte cell count. Increased cell count in innate immune responses in the case of depressed people comes from the fact that depression increases pro-inflammatory cytokines (e.g., IL-1, IL-6 and TNF-α) which are secreted by innate immune system cells. However, when a depressed person regularly rides a bike, the cell counts of both eosinophil and neutrophil granulocyte increased to secrete anti-inflammatory cytokines like IL-6 and IL-10 which help to reduce the effects of depression. Chronic depression is associated with increased cell counts of basophilic, eosinophil, neutrophil granulocytes and monocytes. Again, regular cycling increases cell counts of eosinophil and neutrophil granulocytes and monocytes which leads to the secretion of anti-inflammatory cytokines to lessen the effects of depression. These findings allow us to better understand how depression, innate immune system and exercise (cycling) are related.