Novel aspects of our study are (i) functionally distinct Th9 cells are enriched in the affected joints of RA patients, (ii) endogenously produced synovial IL-9 prolongs neutrophil survival, their activation, and production of MMPs to perpetuate the inflammation of the affected joints of RA, (iii) IL-9 also potentiates inflammatory cytokine producing T helper cells like Th1, Th17, and TNF-α producer (iv) synovial enrichment of Th9 cells correlates with disease severity. Here, IL9 is linked to rheumatoid arthritis.