BACKGROUND: Interleukin (IL)-17 is an important factor in rheumatoid arthritis 
(RA) pathogenesis. MicroRNA (miRNA)s are a family of non coding RNAs and 
associated with human diseases including RA. The purpose of this study is to 
identify the miRNAs in the differentiation of IL-17 producing cells, and analyze 
their expression pattern in the peripheral blood mononuclear cells (PBMC) and 
synovium from RA patients.
METHODS: IL-17 producing cells were expanded from CD4+T cell. MiRNA microarray 
was performed to identify the miRNAs in the differentiation of IL-17 producing 
cells. Quantitative polymerase chain reaction was performed to examine the 
expression patterns of the identified miRNAs in the PBMC and synovium from RA 
and osteoarthritis (OA) patients. Double staining combining in situ 
hybridization and immunohistochemistry of IL-17 was performed to analyze the 
expression pattern of identified miRNA in the synovium.
RESULTS: Six miRNAs, let-7a, miR-26, miR-146a/b, miR-150, and miR-155 were 
significantly up regulated in the IL-17 producing T cells. The expression of 
miR-146a and IL-17 was higher than in PBMC in the patients with low score of 
Larsen grade and short disease duration. MiR-146a intensely expressed in RA 
synovium in comparison to OA. MiR-146a expressed intensely in the synovium with 
hyperplasia and high expression of IL-17 from the patients with high disease 
activity. Double staining revealed that miR-146a expressed in IL-17 expressing 
cells.
CONCLUSION: These results indicated that miR-146a was associated with IL-17 
expression in the PBMC and synovium in RA patients. There is the possibility 
that miR-146a participates in the IL-17 expression.