Molecular Diaries: Connecting the dots. Inflammation and depression in sexual minorities

There is a big health disparity between individuals who are heterosexual and individuals who belong to a sexual minority. That spans cardiovascular diseases, chronic pain, diabetes, arthritis, and beyond. People from sexual minorities are more likely to suffer from the above.

This also holds true for depression, a complex condition with a clear link to our social environment. In case of sexual minorities, the social environment is very often hostile and violent, posing a mental health challenge from early on in life.

How is depression linked to our social environment? The social signal transduction theory of depression proposes that early interpersonal events such as exclusion or abuse are more likely to impact psychological and clinical outcomes than other threats. But what are we able to observe on the molecular level?

When Freud said in 1917 that melancholia behaves like an open wound, he was very right. The same molecular phenomenon that we observe during wounding is present in psychologically challenging situations like interpersonal events, and it’s called: inflammation. It is an immunological mechanism that activates when we are in danger. Or think we are in danger.

During inflammation, the immune system orchestrates a whole response to protect us from a pathogen or an injury. The permeability of the vascular tissue changes so a set of different immune cells can travel to the place of i.e. wounding or infection, and start their many mechanisms to promote healing. This includes a changed genetic program that results in immune cells sending many inflammatory molecules around for the purpose of signaling and fighting off danger. Danger. Danger. But what if on the psychological level, we often feel that we are in danger? What if inflammation doesn’t stop when the danger is over? What if it on some level stays with us?

This is called chronic inflammation and it is exactly what scientists are observing in sexual minorities more than in heterosexuals. A set of correlations: young adults who belong to sexual minorities reported more severe symptoms of depression, had more interpersonal events, and had elevated chronic inflammation. Their blood samples were measured with a time distance and confirmed that inflammation markers stayed with them over longer periods.

One of them was IL-6, a molecule that regulates the balance between two very important sets of immune cells, Th17, that also drive diseases linked to excessive inflammation, and Tregs, cells that control the excessive inflammation, giving the immune system the signal to calm down. Elevated levels of IL-6 lead to multiple sclerosis and rheumatoid arthritis.

Importance of chronic inflammation can be summarized with the title of the following Nature paper: Chronic inflammation in the etiology of disease across the life span. It is central to plethora of diseases, the same ones sexual minorities are more at risk from.

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It is important to approach my interpretation critically. Do I cite the sources? Do I conclude too easily in order to make an argument? Do I underline when two phenomena are correlated, but we still do not understand the causation? All these things are important. Please also note that all statements I have made are to my current knowledge and you are welcome to challenge them. Thank you for reading.