Peripheral interleukin-2 level is associated with negative symptoms and cognitive performance in schizophrenia (original) (raw)

2014, Physiology & Behavior

• Peripheral IL-2 levels correlated positively with performance in tests of working memory and intelligence in patients with schizophrenia. 13 • IL-2 levels correlated negatively with scores in the negative subscale of PANSS. 14 • These associations pose IL-2 as a possible marker of cognitive and affective preservation in schizophrenia. 15 16 1 7 a b s t r a c t 1 8 hibition, language and executive functions [4]. Notwithstanding recent 64 advances, causes underlying SZ as well as its different symptomatic 65 manifestations remain largely unknown. Considering the lack of reliable 66 biomarkers, diagnosis, assessment and prognosis of SZ are based on 67 symptomatology alone, which hinders the implementation of personal-68 ized treatments [5]. 69 In the last decade, immunological alterations in individuals affected 70 by major mental disorders, such as SZ, have received great attention, as 71 they can aid to further elucidate related pathophysiological pathways 72 [6-9]. One of the most promising approaches to evaluate immune 73 changes in SZ is the measurement of cytokines in serum or plasma 74 [10]. Cytokines are molecular mediators of the immune system. They 75 are involved in a complex and redundant network that communicates 76 immune and non immune cells [11]. 77 Interleukin 2 (IL-2) is a cytokine of 15.5kd discovered more than 78 30 years ago. First described as a T cell growth factor, IL-2 is mainly 79 produced by T cells after interaction of MHC/antigen/T-cell receptor 80 (TCR) and co-stimulatory molecules. IL-2 acts as an autocrine and para-81 crine third signal, inducing clonal expansion and effector T and B-cells 82 development. It also plays an important role on innate immunity, lead-83 ing to activation and proliferation of natural killer (NK) cells [12]. Sever-84 al studies have pointed to a potential role of IL-2 in SZ, with most studies 85 reporting altered peripheral levels of IL-2 when compared with healthy 86 controls [13,14], as well as a reduction in production of IL-2 by leuko-87 cytes after mitogen stimulation [15-18]. Nevertheless, association be-88 tween IL-2 and different groups of symptoms of SZ, namely positive, 89 negative and cognitive, has not been explored. 90 The objective of this study was to investigate a possible correlation 91 of peripheral IL-2 levels with symptomatology and cognitive perfor-92 mance of patients with SZ. In addition, we compared serum levels of 93 this cytokine between patients with SZ and healthy controls. We hy-94 pothesized that individuals with SZ would exhibit decreased levels of 95 157 2.4. Statistical analysis 158 Statistical analyses were performed using SPSS 20.0 for Mac. All the 159 distributions of quantitative data were tested for normality using the 160 Kolmogorov-Smirnov test. Comparisons of clinical and demographic 161 variables between SZ group and healthy volunteers group were per-162 formed using X 2 , Student t-test and Mann-Whitney U-test when appro-163 priate. Differences in IL-2 levels between the two groups were evaluated 164 using the Mann-Whitney U-test. Correlation between cognitive tests 165 and biomarker levels was tested using the Spearman correlation coeffi-166 cient. Statistical significance was set in alpha ≤0.05.