Plasma concentrations of soluble cytokine receptors in euthymic bipolar patients with and without subsyndromal symptoms

Forty-five euthymic bipolar patients (22 with subsyndromal symptoms (BD+) and 23 without subsyndromal symptoms (BD-) and 23 well controls (WC) were recruited for assessment of soluble tumor necrosis factor receptor-1 (sTNF-R1), soluble interleukin-6 receptor (sIL-6R) and soluble interleukin-2 receptor (sIL-2R) concentrations. Soluble cytokine receptor concentrations were assessed using enzyme-linked immunosorbent assay.In comparison to WC, sTNF-R1 concentration was higher in both BD- and BD+ (age and sex adjusted standardized β, respectively: β？=？0.34, p？=？0.012 and β？=？0.41, p？=？0.003). Similarly, compared to WC, sIL-6R concentration was higher in both BD- and BD+？(age and sex adjusted standardized β, respectively: β？=？0.44, p？=？0.001 and β？=？0.37, p？=？0.008). There was no difference between BD- and BD+ in the concentration of either sTNF-R1 or sIL-6R; plasma concentration of sIL-2R was not analyzed as 75% percent of the samples were non-detectable.Although bipolar patients present with a pro-inflammatory shift compared to well controls, subsyndromal symptoms are not associated with additive increasing effects. Longitudinal studies with larger samples are required to clarify the relationship between illness course and inflammatory markers in bipolar disorder.Bipolar disorder (BD) has long been considered an episodic illness characterized by complete symptomatic recovery during inter-episodic periods. However, a growing body of evidence shows that the rate of inter-episodic morbidity in the form of subsyndromal symptoms is much higher than previously thought [1,2]. Therefore, early recognition and treatment of subsyndromal symptoms represents an important target for clinicians, given associations with increased risk of relapse, decrement in functioning and cognitive dysfunction [2-4]. However, treatment alternatives are limited for the patients with subsyndromal symptoms, many of whom do not respond adequately to conventional therapies [4].Recent data indicate that