PTGDR2 and rheumatoid arthritis: In accordance with this, we found a significantly decreased frequency of circulating pb ILC2s (defined as LinnegCD127+CD161+CRTH2+ lymphoid cells) in patients suffering from various chronic inflammatory and fibrotic diseases affecting different organ systems (cystic fibrosis - CF, inflammatory bowel diseases - IBD and rheumatoid arthritis - RA) compared to healthy controls (Figures 1A,B).