Gene expression of inhibitory receptors and immune regulatory molecules in polarized macrophages derived from early- and late-stage BD patients

Abstract

Background: Bipolar disorder (BD) has been associated with increased levels of peripheral inflammatory mediators and neuroinflammation. Previously, we observed different immune responses in macrophages of BD patients at different stages of the disorder. Thus, we aimed to further evaluate the regulation of immune response in BD by quantifying the expression of immune checkpoint receptors and respective ligands, as well as molecules involved in regulation and transcription of inflammatory mediators in polarized macrophages of early and late stages individuals with BD. Methods: qRT-PCR was performed to analyze the expression of genes involved in immune regulation, such as TLR1, TLR6, PD-1, NFKB1, PD-L1, PD-L2 and TIM-3 in samples of proinflammatory M1 or M(IFNγ+LPS) and anti-inflammatory M2 or M(IL-4) macrophages derived from peripheral blood mononuclear cells (PBMCs) of euthymic BD patients (n=16), classified as early-stage BD (BD-E, n=9) and late-stage BD (BD-L, n=7) - according to Functional Assessment Short Test (FAST) - and healthy controls (HC, n=10). Results: M(IL-4) from BD-E showed higher expression levels of NFKB1 and PD-L1 in comparison to HC (p<0.05), while BD-L only had higher expression levels of PD-L1 compared to HC (p<0.05). No statistical differences were found between groups for the expression levels of TLR1, PD-L2 and TIM-3 in M(IL-4) phenotype, while expression levels remained unchanged in M(IFNγ+LPS) for all markers. TLR6 and PD-1 did not show PCR amplification in both macrophages phenotypes. Conclusion: Our findings suggest an immunological regulation acting as a compensatory mechanism by M2 anti-inflammatory macrophages at early stage of BD, although decreased regulation in these cells seems to be observed at late stages of the disorder. On the other hand, the impairment function of proinflammatory macrophages at late stages of BD might underlie a different immunologic mechanism, such as senescence. We hypothesize that such alterations are possibly due to persistent chronic low-grade inflammation during the course of BD that results in the ‘exhaustion’ of macrophage response. However, further investigation is required to better comprehend the role of immune regulatory mechanisms in the disorder.