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Background Micro RNAs (mi RNAs) gene expression regulators are altered in psoriasis suggesting their role in the pathogenesis. Objective To study expression changes of inflammation and toll-like receptor ( TLR)-related mi RNAs, mi RNA-155, let-7i, mi RNA-21, mi RNA-146a and mi RNA-223 in peripheral mononuclear cells ( PBMCs) and mi RNA-21, mi RNA-146a and mi RNA-223 in plasma, from chronic plaque-type psoriasis patients who were treatment-naive or had undergone a washout period ( n = 11). Mi RNAs were evaluated at baseline and after 11 (9-12) months [median (25th-75th percentile range)] of methotrexate ( MTX) or topical (betamethasone plus calcipotriene) treatment. Methods Mi RNA expression was analysed with quantitative real-time reverse transcription-polymerase chain reaction. Matched controls were studied. Results Psoriasis patients presented, at baseline, increased expression of mi RNA-155, let-7i, mi RNA-146a, mi RNA-21 and mi RNA-223 in PBMCs, plus mi RNA-21, mi RNA-146a and mi RNA-223 in plasma. Receiver-operator characteristic ( ROC) curve analysis and area under the curve ( AUC) showed that expression of these mi RNAs have the potential to distinguish between psoriasis and controls. At baseline, mi RNA-155 expression in PBMCs correlated with Psoriasis Area Severity Index ( PASI) [12 (8-14)] (Spearman r: 0.7140, P < 0.05) suggesting a role in psoriasis. After MTX or topical treatment, reduction in PASI was observed [87.5% (75-100)]; mi RNA-155 expression in PBMCs decreased; plasma mi RNA-21, mi RNA-146a and mi RNA-223 were down-regulated. ROC analysis showed that mi RNA-155 expression in PBMCs from psoriasis patients have the potential to distinguish between patients' samples at baseline and after treatment ( AUC: 0.942, sensitivity: 0.91; specificity: 0.91 values; maximum likelihood ratio =10). After treatment, mi RNA-146a expression in PBMCs increased; mi RNA-155/mi RNA-146a ratio decreased, suggestive of a regulatory feedback; let-7i expression decreased; mi RNA-21 and mi RNA-223 remained elevated. Conclusion In this exploratory study, psoriasis patients presented increased expression of mi RNA-155 in PBMCs that correlated with PASI and decreased with disease remission. Mi RNA-21, mi RNA-146a and mi RNA-223 in PBMCs and plasma were increased at baseline and differentially modulated, underscoring different roles of TLR-related mi RNAs in psoriasis. [ABSTRACT FROM AUTHOR]