PTGER4 and systemic lupus erythematosus: As shown in Figure 4, SLE patients presented with a higher level of serum EP1 (P = 0.001, Figure 4A), EP2 (P = 0.009, Figure 4B), EP3 (P = 0.001, Figure 4C), EP4 (P < 0.001, Figure 4D), EP6 (P < 0.001, Figure 4F), and EP10 (P = 0.044, Figure 4J), while the levels were similar in EP5 (Figure 4E), EP7 (Figure 4G), EP8 (Figure 4H), and EP9 (Figure 4I) between two groups.