The coagulation fXIII is a crucial determinant of inflammation and bone erosion in rheumatoid arthritis in mice. Although reduced inflammation is a common feature between fibrinogen-deficient and fXIII-deficient mice after CIA, reduction of osteoclasts is a unique feature of fXIII-deficient mice. Histologic images are from Figure 5A in the article by Raghu et al that begins on page 427.