Background and objective:Little is known about the correspondence of cytokines detected among the different biological matrices used in periodontal research and whether locally-detected cytokine mRNA can also be identified at the translated protein level. The aims of this study were to compare: (a) the detection of classic cytokines at protein level in corresponding samples of serum, gingival tissue and gingival crevicular fluid (GCF) in subjects with periodontitis and (b) the detection of cytokines at protein level in GCF and tissue with their detection at mRNA level in tissue. Material and methods:Protein concentrations of IL-1β, IL-6 and TNFα were measured in corresponding samples of GCF, gingival tissue and serum from 125 subjects with chronic periodontitis by multiplex immunoassay. The mRNA levels of these cytokines were evaluated in the same gingival tissue by qPCR. Results:The mean protein concentrations of IL-1ß and TNFα were higher in tissue and GCF than in serum (P < 0.05). The mean protein concentration of IL-6 was higher in tissue, followed by serum and GCF, respectively (P < 0.05). Using serum as the gold standard, detection of IL-1ß in GCF and IL-6 in tissue had the highest sensitivity (100%), while detection of IL-6 in the GCF had the lowest sensitivity (77.9%). Using tissue as the gold standard, the detection sensitivities of IL-1ß, IL-6 and TNFα were 93.6%, 78.4% and 94.2%, respectively, in GCF. Using mRNA as the gold standard, the detection of IL-1ß and IL-6 at the protein level in tissue (100.0%) had the highest sensitivity, while the detection of IL-6 in GCF (77.9%) had the lowest sensitivity.Conclusion: Tissue and GCF exhibited overall higher protein concentrations of cytokines than serum. GCF presented good reliability for identifying the target cytokines at protein level, when compared with detecting tissue cytokines at protein level. GCF and tissue presented high sensitivities for detecting cytokines at the protein level, when compared with detecting tissue cytokines at the mRNA level. The sensitivity for the identification of cytokines in the GCF depended on the target cytokine, where IL-6 was the least likely cytokine to be detected in this matrix. K E Y W O R D Scytokines, mRNA, protein levels | 175 DUARTE ET Al.