Systemic disorders contribute to the mental health of the
patient. Depression can reduce the functional parameters of immune system.
Meanwhile innate, non-specific inflammation is related to depressed moods.
Chronic age-related systemic diseases can cause reasons for morbidity of
depression in advanced age groups.
Inflammation is an immune response to any
pathogens or tissue damage mediated by macrophages which are large white blood
cells involved in the body's defense mechanism. These release pro-inflammatory
cytokines that causes inflammatory response.
Depression is a mental disorder with commonly seen symptoms
such as loss of interest, low energy, disturbed sleep or appetite and poor
cytokines such as interleukin (IL)-6, IL-1b, and especially, tumor necrosis
factor (TNF)-alpha are known to have effects on depressed moods. Animal studies have
shown that peripheral pro-inflammatory cytokines could penetrate the blood
brain barrier and stimulate the production of central pro-inflammatory
cytokines that regulates the moods. When humans were administered immune
stimulating endotoxins that cause low-grade inflammation, episodes of major
depression was recorded. Hence increased level of cytokines in blood is related
to the symptoms of depression.
Negative mood causes high level of circulating pro-inflammatory
cytokines. Depression activates the hypothalamic-pituitary-adrenal axis that
leads to release of cortisol, which aggravates sympathetic stimulus (the fight
or flight response) and reduces parasympathetic stimulus (the rest and digest
response). This increases pro-inflammatory cytokines in blood which then cause
inflammation in the body.
Hence this is a complex feedback network involving central nervous
system, endocrine system and immune system. These act in modulation of
peripheral inflammatory response to maintain peripheral homeostatic balance.