The immune system is linked to an increasing number of medical diseases, including lately also severe mental disorders. Hence, infections, autoimmunity and other immune responses could be involved in the pathogenesis of some patients with severe mental disorders.

Our large-scale epidemiological studies have consistently displayed that infections and autoimmune diseases increases the risk of developing severe mental disorders in a dose-response relationship, where the risk of severe mental disorders particularly increases with the amount of infections exposed to. It is a broad range of infections and autoimmune diseases that are associated with an increased risk of severe mental disorders, with the more severe infections increasing the risk the most. The risk of severe mental disorders is particularly increased with the temporal proximity to the infection. Furthermore, we have shown that the genetics for psychosis does not explain the association with infections but that the genetics and infections are additive risk factors for psychosis.  Moreover, at diagnosis there are elevated levels of inflammatory markers in the blood and studies on the cerebrospinal fluid surrounding the brain have shown some evidence for elevated immune markers in the brain and signs of disrupted blood-brain barrier in some of the patients, making them more vulnerable to potential detrimental effects of immune components. Our meta-analyses of randomized clinical trials have shown that anti-inflammatory treatment seems to be effective for depression and depressive symptoms and also for psychotic disorders in addition to antipsychotic treatment but intensive work is under way to identify subgroups that would be most likely to respond to anti-inflammatory add-on treatment, which might results in clinical impact.

Psychiatric symptoms can be directly triggered by infections reaching the brain, or be secondary to systemic inflammation indirectly affecting the brain through immune components, such as brain-reactive antibodies and cytokines. Nonetheless, shared genetic factor or other unmeasured environmental factors might account for some of this increased prevalence of immune-related diseases among individuals with psychosis; however, the common genetic variants associated with schizophrenia does not seem to increase the susceptibility for acquiring infections. Hence, a thorough differential diagnostic assessment of immune-related diseases, signs of neuroinflammation or other detectable physical diseases are of utmost importance in individuals with psychosis, particularly during onset of symptoms, to improve the psychiatric symptoms, survival rates and quality of life.

Learning Objectives: 

1. The association between infections and mental disorders
2. The association between autoimmune diseases and mental disorders