Distribution of soluble CD14 according to ethnicity and sex is shown in the figure. Median and interquartile ranges are indicated by the band and box edges, respectively. The whiskers indicate upper limits.

The rank correlation coefficient between sCD14 and CRP, fibrinogen, and IL-6 were 0.22, 0.21, and 0.17, respectively (all P<0.001). In age-, race-, and sex-adjusted models, sCD14 was positively correlated with baseline smoking, diabetes mellitus, fasting glucose, hypertension, and negatively correlated with BMI (all P<0.001; Table 1). The differences in sCD14 by race and sex persisted after adjusting for CVD risk factors (Table 1). When adjusted for baseline CHD and CVD risk factors, sCD14 was strongly and independently associated with other inflammatory and acute phase proteins, including CRP, IL-6, and fibrinogen, as well as with increased internal carotid artery wall thickness and decreased ABI (all P<0.001).

The estimate of sCD14 phenotypic variance explained by genomewide SNPs was 33.17% (P=0.03). In the genomewide association scan of 2952 EA and 528 blacks, 2 regions, 1q24 and 5q31, reached genomewide significance in EA (Figure I in the online-only Data Supplement); the chromosome 5q31 peak was also genomewide significant in blacks (Figure II in the online-only Data Supplement). Results for the lead (index) SNPs associated with sCD14 in each genomic region are summarized in Table 2. In EA, the strongest genomewide association signal was located on chromosome 5q31, centered around the CD14 structural gene.

To our knowledge, family-based estimates of sCD14 heritability have not been previously reported. Therefore, we estimated the amount of phenotypic variance of sCD14 explained by distant genetic relationships between individuals with the CHS EA population by applying the Genome-wide Complex Trait Analysis method using all genotyped autosomal SNPs.

In the EA genome-wide association study (GWAS), a second region on chromosome 1q24.3 achieved genomewide significance. The index SNP rs1063412 at 1q24.3 is a C/T polymorphism that encodes a Pro266Ser amino acid substitution within the second exon of PIGC (MAF=0.43). According to the HapMap, the C allele (Pro266) is the minor allele in European and Asian populations, but is the major allele in African populations. The C allele (MAF=0.43 in CHS EA) was associated with 488 ng/mL lower sCD14 (P=1.4x10^-8).

To further explore the CD14 gene variants associated with sCD14 in EA and blacks, we used denser CD14 genotype data from the IBC array, which contains 15 SNPs covering the CD14 coding, intronic, untranslated, and flanking regions. In EA, the most strongly associated SNP on the IBC array was rs5744455 (P=3.5x10^-26), located 50 bp upstream of the transcription start site. On the basis of 1000 Genomes Centre d'Etude du Polymorphisme Humain (CEU) data, this SNP is in strong LD with the index GWAS SNP, rs5744441 (LD r2=1.0). After conditioning on rs5744455, probability values for 3 additional SNPs in the CD14 region were significant at the Bonferroni-adjusted threshold of POf cardiovascular causes (hazard ratio=1.13; 95% CI=1.05-1.22; P=0.001) and death because of non-cardiovascular causes (hazard ratio=1.11; 95% CI=1.04-1.18; P=0.001). Table II in the online-only Data Supplement shows the association of each inflammation biomarker with mortality in multivariable models, including all the inflammation biomarkers. In these models, sCD14 and IL-6 were each independently associated with mortality, whereas CRP and fibrinogen were not. When analyzed categorically, there was a graded, linear increase in mortality risk with each successive sCD14 quintile. Compared with the bottom quintile, the hazard ratios (95% CIs) for the second, third, fourth, and fifth quintile were 1.00 (0.87-1.14), 1.02 (0.89-1.16), 1.12 (0.98-1.27), and 1.27 (1.11-1.45), respectively. The hazard ratios comparing top with bottom quintiles for cardiovascular death and non-cardiovascular were 1.26 (95% CI 1.01-1.57; P=0.04) and 1.32 (95% CI 1.11-1.57; P=0.002), respectively.

In blacks, several other SNPs on the IBC array had more significant P values than the index SNP from the black GWAS rs778584. The lead SNP from the IBC analysis was rs5744451 (MAF=0.09), which was associated with 27936 ng/mL lower sCD14 (P=1.31x10^-14). Rs5744451 is located in the 5' flanking region of CD14. This SNP was not successfully imputed and hence not included in the GWAS analysis. After conditioning on rs5744451, 3 additional CD14 SNPs (rs5744455, rs2569191, and rs778584) had P<0.003. Haplotype analysis confirmed that rs5744451 tags a second CD14-lowering haplotype that is common among blacks but rare among EA (Table 3).

Relationship of sCD14 to Incident CVD and Mortality

Among the 5462 EA and black participants with measured sCD14 at the CHS baseline examination, there were incident MI, 1547 incident CHD, 945 incident strokes, 3820 deaths during the 20-year follow-up period. Of the deaths, 1519 were attributed to cardiovascular causes.

Among the sCD14-associated SNPs identified in our GWAS, there was no association with risk of mortality in either ethnicity of CHS (Table III in the online-only Data Supplement). In CHS, the minor alleles of CD14 rs4914 and rs778584 were each nominally associated with 1.3- to 1.6-fold increased risk of stroke in black, whereas rs778584 was associated with decreased risk of CHD in EA (P=0.025). However, these results were not significant when corrected for multiple hypothesis testing. Nor was there significant evidence for association between CD14 genotype and risk of CHD or stroke in a second, large case-control sample from the Women's Health Initiative (Table IV in the online-only Data Supplement).