IL9 and rheumatoid arthritis: Firstly, to clarify our hypothesis that IL-26 was involved in IL-9 production in macrophages of rheumatoid arthritis, synovial tissue from RA patients was collected and stained by hematoxylin and eosin (H&E) for identification of leukocyte infiltration and stained by immunofluorescence for checking the location of IL-26 and IL-9.