2010). Furthermore, EP4 receptors have shown to be involved in PGE2 stimulation of Th1 differentiation and Th17 expansion contributing to arthritis and EP4 antagonists were effective in blocking the development of arthritis in a mouse model of type II collagen arthritis (Chen et al. 2010). The EP4 antagonist (compound 3) was highly effective in reducing arthritic lesions in a rat model of type II collagen arthritis as demonstrated by the reduction in quantitative arthritic score for knee joints (Fig. 9) as well as in histopathology of joint (Fig. 10). Here, PTGER4 is linked to Arthritis.