Many authors have suggested that the in vitro secretion of cytokines by peripheral blood cell preparations is the most appropriate way to investigate the involvement of cytokines in schizophrenia. In fact, circulating cytokine levels found in plasma and/or serum may be produced by blood cells, endothelium, or may originate from the brain and may not reflect tissue levels. In addition, systemic factors that are unrelated to psychiatric and neurological disorders may influence circulating levels of cytokines. Thus, measurement of the production of cytokines by PBMC may better reflect their potential to contribute to inflammation compared to assessment of serum cytokine levels. The present study provides a comparative evaluation of cyto-chemokine production by PBMC from schizophrenic patients and from healthy controls.
Abnormal regulation of cyto-chemokine activity may contribute to pathophysiology and clinical manifestations in schizophrenic subjects. The evidence of reciprocal communication between immune and nervous systems and the altered immunological state in psychiatric diseases have contributed to the ''cytokine hypothesis''. On the other hand cytokines, either directly or indirectly from the periphery, are able to play a role in signaling the brain to produce neurochemical, neuroendocrine, neuroimmune, and behavioral changes [30
]. So far, the majority of studies in psychiatry have investigated small cyto-chemokine subsets, mainly pro-inflammatory molecules such as IL-1, IL-6, TNFα, CXCL9 and CXCL11 under various in vitro conditions with peripheral blood preparation, as well as in vivo
in various body fluid such as in plasma, serum, CSF and urine of patients with schizophrenia [14
]. Modified production of cytokines, with conflicting data on circulating serum levels of IL-6, TNFα has been reported. Ganguli et al have demonstrated a positive association of the serum IL-6 levels with duration of illness, while Erbagci et al. have not found an altered plasma levels of IL-6 and TNFα in drug-free schizophrenic patients on acute exacerbation [34
In this study we have analyzed the production of a number of additional cytokines and chemokines, previously studied [11
], as well as some non-previously studied in schizophrenia. LPS are potent and pleitropic stimuli for cells of the immune system. Stimulation of PBMC by LPS leads to the release of cytokines and other inflammatory mediators. LPS activates nuclear localization of transcription factor nuclear factor kB (NF-kB) and subsequent activation of genes in the proinflammatory pathways. On the basis of previous studies from our lab and other groups, LPS (10 mg/ml) dosage and the incubation time have been shown to induce the maximal stimulation for the PBMC release of proinflammatory cytokines.
The present results demonstrate that production of MCP-1, MIP-1α, IL-8 and IL-18 are significantly higher in cell culture supernatants of PBMC from patients with schizophrenia respect to age and gender-matched HC, reinforcing the findings that schizophrenia is accompanied by an activation of the monocyte-macrophage arm of cell-mediated immunity [36
]. We have observed a high level of IL-18, that induces the activation of Th1 cells, which may justify the reduced IFN-γ release observed in our schizophrenic patients when compared to healthy subjects, in accordance with previous reports that showed decreased IFNγ production in PBMC from schizophrenic patients [37
]. Moreover, the lower levels of RANTES, a selective attractant for memory T lymphocytes associated with the development of polarized Th1-type cellular responses, fits well with the lower production of IFNγ in schizophrenic patients. The observed decreased production of RANTES and increased levels of MCP-1, a chemokine associated with the Th2-type responses, in our SC subjects points to a blunted production of related Th1 molecules and to an under-activation of the Th2 system in schizophrenia, confirming an alteration of the Th1/Th2 balance as hypothesized by other authors [12
]. RANTES and IFN-γ production that was lower in SC than HC, after LPS stimulation showed greater improvement, while the other cyto-chemokine production that was higher in SC than HC showed less improvement after LPS stimulation. A weakly negative correlation was observed between the relative variation of INF-γ and the basal value of IL-18 (ρ = -0.215, p = 0.176) and between the relative variation of RANTES and the basal value of MCP-1 (ρ = -0.174, p = 0.178). Since the biological functions of cytokines are physiologically interconnected, it might be expected that there would also be an aberrant regulation of RANTES and IFN-γ production in SC patients, thus altered cyto-chemokines production might represent a biological state marker for PBMC in SC.
Atypical antipsychotics are becoming standard drugs for the treatment of schizophrenia due to their less adverse effects and the possible greater effectiveness for the negative symptoms of the illness. Some studies often have yielded dissimilar or conflicting results regarding the effect that atypical antipsychotics may have on the cytokine system [39
], and associations between changes in the levels of cytokines and the therapeutic response have not been firmly established. Based on the information available at present, atypical antipsychotics appear to offer the same degree of safety in both short-term and long-term treatment of schizophrenia. To speculate the influence of antipsychotics on the cytokine system in SC patients we have evaluated PBMC released and serum levels of MCP-1, RANTES and IL-18 in SC patients after short-term atypical antipsychotic treatment.
This preliminary study, including the relatively low sample size, merely demonstrates that levels of IL-18 and RANTES are increased in PBMC from treated SC patients, while MCP-1 levels are decreased. The comparison between the cyto-chemokine aberrations observed in supernatants of PBMC from SC patients after neuroleptic treatment and cyto-chemokine levels in supernatants of PBMC from healthy controls are still increasingly different.
In addition, we have observed that the antipsychotic treatment did not significantly modulate IL-18, MCP-1 and RANTES serum levels. Discrepancies often arise between data derived from levels of cyto-chemokines produced in vitro by cultured PBMC and in vivo levels in the serum due to the cytokines short half-life, and high concentrations reached at the sites of release, but having much lower concentrations in the blood.
The data presented here suggests that alteration of these selected cytokines could be related to the disease per se, but more SC patients must be analyzed to clarify the effect of treatment with atypical antipsychotic drug such as risperidone, olanzapine and clozapine on cyto/chemokines production. Further studies are required to better recognize the alteration in the cytokine networks during antipsychotic treatment to clarify the relationship with a clinical response. Our data confirmed and extend the previous findings that altered inflammation-related pathways characterize schizophrenia. The inflammatory response connected with increased levels of IL-8, MCP-1, MIP-1α and IL-18 released by PBMC may demonstrate that physiological differences can indeed be identified in the brain and also in the peripheral blood of schizophrenic subjects.