CCL4 and inflammatory bowel disease: In the subsequent mediation analysis using a threshold of p < 1 × 10−5, we found that CCL4 played a mediating effect in the associations between 4 lipids [Sterol ester (27:1/22:6), Phosphatidylcholine (16:0_20:4), Phosphatidylcholine (17:0_18:2), Sphingomyelin (d38:1)] and IBD, with mediated proportions of 7.46%, 3.61%, 3.53%, and 5.46%, respectively (Table 1).