When I was in 6th grade, I was diagnosed with a form of juvenile arthritis, a chronic autoimmune disorder that causes inflammation and pain in any number of joints. Causes may be hereditary and the onset often involves an accident. My arthritis began in my left wrist, but it spread to my right wrist, ankles, knees, back, hips quickly. Since it is a relatively uncommon disease, it took 9 months for a proper diagnosis, in which we had no idea what was wrong with me. I missed a lot of school to go to doctor’s appointments and my teachers were not happy. I began to develop symptoms of depression do to the isolation I felt on a daily basis. My parents and doctors were not surprised by this since I had just learned that I would probably have chronic pain for the rest of my life; however, when I was doing research for my third paper, I came across an article that explained another reason for these sudden symptoms. This article explains that cancer and rheumatoid (juvenile) arthritis can lead depression due to the effects of the immune system’s cytokines on the brain.
In 1990, scientists noticed that some patients suffering from clinical depression had higher concentration of inflammatory biomarkers in their blood, which led to the hypothesis that pro-inflammatory cytokines released from the immune system are responsible for many of the clinical aspects of depression like sleep disturbance, decreased energy, changes in eating patterns, and hyperactivity of the hypothalamus-pituitary-adrenal axis. When the body is infected with disease, the immune system releases pro-inflammatory cytokines that are able to cross the blood-brain barrier. The cytokines affect the central amygdala, hypothalamus, medulla, which not only causes “sick behavior” but also increases the risk of major depressive disorder. Additionally, stimulation of the immune system by injecting certain cytokines (IL-1ß and TNF-α) creates depression-like disorders in humans and animals, which can be relieved with anti-depressants that work on dopamine, norepinephrine, and serotonin.
Although this cannot be the only explanation for depression (since not all depressed patients also have autoimmune disorders), I found this incredibly interesting and personally relevant.