Rheumatoid arthritis - Ornithorhynchus anatinus (platypus)

Rheumatoid arthritis (RA) is a chronic autoimmune joint disease where persistent inflammation affects bone remodeling leading to progressive bone destruction. In RA, abnormal activation of the immune system elevates pro-inflammatory cytokines and chemokines levels, which can promote synovial angiogenesis and leukocyte infiltration. The synovium forms a hyperplastic pannus with infiltrated macrophage-like and fibroblast-like synoviocytes and invades joints by secreting proteinases and inducing osteoclast differentiation.