Free Interleukin (IL)-18 levels, and the impact of IL18 and IL18BP genetic variation, in CHD patients and healthy men.

OBJECTIVE To investigate free interleukin-18 (fIL-18) levels, and variation within the IL-18 system genes, in heart surgery patients, and healthy men. METHODS AND RESULTS fIL-18 was calculated from IL-18 and IL-18 binding protein (BP) levels, in 421 healthy men and 196 post-coronary artery bypass graft (CABG) patients. After surgery, fIL-18 peaked at 6 hours (from 117 to 331 pg/mL) but fell to below presurgery levels at 24 hours (99 pg/mL), because of changes in total IL-18 and IL-18BP. fIL-18 24 hours postsurgery was significantly higher in those who suffered a major complication after surgery (125 versus 80 pg/mL, P<0.01). Baseline total IL-18 was also higher in healthy men who went on to suffer an MI over 17 years of prospective study (276 versus 240 pg/mL, P=0.01). Tagging SNPs for IL18 (n=5) and IL18BP (n=3) were determined, in both studies the IL18 HapIII haplotype (frequency 30%) was associated with 36% lower baseline fIL-18 levels before surgery (P<0.01), and 7% lower in healthy men (P=0.04). The frequency of HapIII was lower in CABG patients than in healthy men (20.7 versus 29.8%, P<0.01). CONCLUSIONS IL-18 levels, which are determined in part by variation in IL18, play a role in CHD development and postsurgery outcome.