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   Mind and body: Scientists identify immune system link to mental illness   
      
   Date:   
   August 13, 2014   
   Source:   
   University of Cambridge   
      
   Mental illness and chronic physical illness such as coronary heart disease and   
   type 2 diabetes may share common biological mechanisms, research suggests.   
      
      
   Children with high everyday levels of a protein released into the blood in   
   response to infection are at greater risk of developing depression and   
   psychosis in adulthood, according to new research which suggests a role for   
   the immune system in mental    
   illness.   
   The study, published in JAMA Psychiatry, indicates that mental illness and   
   chronic physical illness such as coronary heart disease and type 2 diabetes   
   may share common biological mechanisms.   
      
   When we are exposed to an infection, for example influenza or a stomach bug,   
   our immune system fights back to control and remove the infection. During this   
   process, immune cells flood the blood stream with proteins such as   
   interleukin-6 (IL-6), a tell-   
   tale marker of infection. However, even when we are healthy, our bodies carry   
   trace levels of these proteins -- known as 'inflammatory markers' -- which   
   rise exponentially in response to infection.   
      
   Now, researchers have carried out the first ever longitudinal study -- a study   
   that follows the same cohort of people over a long period of time -- to   
   examine the link between these markers in childhood and subsequent mental   
   illness.   
   A team of scientists led by the University of Cambridge studied a sample of   
   4,500 individuals from the Avon Longitudinal Study of Parents and Children --   
   also known as Children of the 90s -- taking blood samples at age 9 and   
   following up at age 18 to see    
   if they had experienced episodes of depression or psychosis. The team divided   
   the individuals into three groups, depending on whether their everyday levels   
   of IL-6 were low, medium or high. They found that those children in the 'high'   
   group were nearly    
   two times more likely to have experienced depression or psychosis than those   
   in the 'low' group.   
      
   Dr Golam Khandaker from the Department of Psychiatry at the University of   
   Cambridge, who led the study, says: "Our immune system acts like a thermostat,   
   turned down low most of the time, but cranked up when we have an infection. In   
   some people, the    
   thermostat is always set slightly higher, behaving as if they have a   
   persistent low level infection -- these people appear to be at a higher risk   
   of developing depression and psychosis. It's too early to say whether this   
   association is causal, and we are    
   carrying out additional studies to examine this association further."   
      
   The research indicates that chronic physical illness such as coronary heart   
   disease and type 2 diabetes may share a common mechanism with mental illness.   
   People with depression and schizophrenia are known to have a much higher risk   
   of developing heart    
   disease and diabetes, and elevated levels of IL-6 have previously been shown   
   to increase the risk of heart disease and type 2 diabetes.   
   Professor Peter Jones, Head of the Department of Psychiatry and senior author   
   of the study, says: "Inflammation may be a common mechanism that influences   
   both our physical and mental health. It is possible that early life adversity   
   and stress lead to    
   persistent increase in levels of IL-6 and other inflammatory markers in our   
   body, which, in turn, increase the risk of a number of chronic physical and   
   mental illness."   
      
   Indeed, low birth weight, a marker of impaired fetal development, is   
   associated with increased everyday levels of inflammatory markers as well as   
   greater risks of heart disease, diabetes, depression and schizophrenia in   
   adults.   
   This potential common mechanism could help explain why physical exercise and   
   diet, classic ways of reducing risk of heart disease, for example, are also   
   thought to improve mood and help depression. The group is now planning   
   additional studies to confirm    
   whether inflammation is a common link between chronic physical and mental   
   illness.   
      
   The research also hints at interesting ways of potentially treating illnesses   
   such as depression: anti-inflammatory drugs. Treatment with anti-inflammatory   
   agents leads to levels of inflammatory markers falling to normal. Previous   
   research has suggested    
   that anti-inflammatory drugs such as aspirin used in conjunction with   
   antipsychotic treatments may be more effective than just the antipsychotics   
   themselves. A multicentre trial is currently underway, into whether the   
   antibiotic minocycline, used for the    
   treatment of acne, can be used to treat lack of enjoyment, social withdrawal,   
   apathy and other so called negative symptoms in schizophrenia. Minocycline is   
   able to penetrate the 'blood-brain barrier', a highly selective permeability   
   barrier which    
   protects the central nervous system from potentially harmful substances   
   circulating in our blood.   
      
   The 'blood-brain barrier' is also at the centre of a potential puzzle raised   
   by research such as today's research: how can the immune system have an effect   
   in the brain when many inflammatory markers and antibodies cannot penetrate   
   this barrier? Studies    
   in mice suggest that the answer may lie in the vagus nerve, which connects the   
   brain to the abdomen. When activated by inflammatory markers in the gut, it   
   sends a signal to the brain, where immune cells produce proteins such as IL-6,   
   leading to increased    
   metabolism (and hence decreased levels) of the 'happiness hormone' serotonin   
   in the brain. Similarly, the signals trigger an increase in toxic chemicals   
   such as nitric oxide, quinolonic acid, and kynurenic acid, which are bad for   
   the functioning of nerve    
   cells.   
      
   Story Source:   
   The above story is based on materials provided by University of Cambridge.   
   Note: Materials may be edited for content and length.   
      
   Journal Reference:   
   Golam M. Khandaker, Rebecca M. Pearson, Stanley Zammit, Glyn Lewis, Peter B.   
   Jones. Association of Serum Interleukin 6 and C-Reactive Protein in Childhood   
   With Depression and Psychosis in Young Adult Life. JAMA Psychiatry, 2014; DOI:   
   10.1001/   
   jamapsychiatry.2014.1332   
      
   Cite This Page:   
   MLA APA Chicago   
   University of Cambridge. "Mind and body: Scientists identify immune system   
   link to mental illness." ScienceDaily. ScienceDaily, 13 August 2014.    
      
      
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