Increased soluble interleukin‐2 receptor concentrations in suicide attempters

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Abstract
Several biochemical parameters such as monoamines and corticosteroids are considered to play a role in the underlying pathogenetic mechanisms in mood disorders. It has also been proposed that disturbances of the immune system may be responsible for mental disorders. Increased concentrations of plasma soluble interleukin-2 receptor (S-IL-2R) reflect an activation of T-lymphocytes. In plasma samples from medication-free suicide attempters with various psychiatric diagnoses (mainly mood disorders), we found a median S-IL-2R concentration far above the range of healthy controls. No sex differences and no differences between diagnostic and suicidal subgroups were noted. In follow-up samples, the S-IL-2R remained at high levels. In cerebrospinal fluid samples from patients, S-IL-2R levels were all below 200 U/ml. No samples from controls were available. We were unable to find pronounced associations between plasma S-IL-2R and various monoaminergic measures in plasma, 24-h urine and cerebrospinal fluid. There was, however, a tendency of an association between S-IL-2R and the ratio of norepinephrine-epinephrine in 24-h urine, as well as plasma and cerebrospinal fluid 4-hydroxy-3-methoxymethylglycol. There was no significant association between post-dexamethasone plasma cortisol, 24-h urinary cortisol and plasma S-IL-2R. Both when studied as medication-free inpatients and during follow-up as outpatients, there were no apparent associations between ratings of psychopathology and plasma S-IL-2R. This study clearly shows that an imbalance of the immune system was present in psychiatric patients studied after a suicide attempt. Furthermore, the immune dysfunction, shown as high S-IL-2R, seems to be independent of drug therapy.