Evidence has suggested that immune imbalance is involved with bipolar disorder (BD); however, its precise mechanism is poorly understood.

This study investigated whether biochemical changes in the serum from BD patients could modulate the phenotype of macrophages.

Eighteen subjects with BD and healthy individuals (n = 5) were included in this study. The human monocyte cell line U-937 was activated with PMA (phorbol 12-myristate 13-acetate) and polarization was induced with RPMI-1640 media supplemented with 10% serum from each patient for 24 h. Gene expression of selected M1 and M2 markers was assessed by qPCR.

Macrophages exposed to serum of manic and depressive BD patients displayed an increase of IL-1β (6.40 ± 3.47 and 9.04 ± 5.84 versus 0.23 ± 0.11; P < 0.05) and TNF-α (2.23 ± 0.91 and 2.03 ± 0.45 versus 0.62 ± 0.24; P = 0.002 and P = 0.004, respectively) compared to remitted group. In parallel, U-937 macrophages treated with serum of patients in acute episode displayed a down-regulation of CXCL9 (0.29 ± 0.20 versus 1.86 ± 1.61; P = 0.006) and CXCL10 expression (0.36 ± 0.15 and 0.86 ± 0.24 versus 1.83 ± 0.88; P < 0.000 and P = 0.04) compared to remitters.

Our results are consistent with previous studies showing that changes in peripheral blood markers could modulate M1/M2 polarization in BD. The evidence of macrophages as source of inflammatory cytokines might be helpful to unravel how the mononuclear phagocyte system can be involved in the etiology of BD.

The authors have not supplied their declaration of competing interest.