The Immunoseasonal Theory of Psychiatric Disorders

Although the influence of the weather on the well-being and mental health of psychiatric patients has been widely seen, the relationships between various seasonal weather factors and depressive, manic, anxiety, and psychotic states have not been systematized in the literature. The current article describes the seasonal changes in weather-related immune responses and their impact on the development of episodes of depression, mania, psychosis, and anxiety, highlighting the T-helper 1 (Th1) and Th2 immune balance as their potential trigger. In autumn–winter depression, the hyperactivation of the Th1 system, possibly by microbial/airborne pathogens, may lead to the inflammatory inhibition of prefrontal activity and the subcortical centers responsible for mood, drive, and motivation. Depressive mood periods are present in most people suffering from schizophrenia. In the spring and summertime, when the compensating anti-Th1 property of the Th2 immune system is activated, it decreases the Th1 response. In individuals immunogenetically susceptible to psychosis and mania, the inhibition of Th1 by the Th2 system may be excessive and lead to Th2-related frontal and subcortical hyperactivation and subsequent psychosis. In people suffering from bipolar disorder, hyperintense changes in white matter may be responsible for the partial activation of subcortical areas, preventing full paranoid psychosis. Thus, psychosis may be mood-congruent in affective disorders.