We investigated the role of the KIR loci and their HLA class I ligands in a large cohort of African American multiple sclerosis (MS) patients (N=907) and controls (N=1456). No significant differences in carrier frequencies for any KIR locus or haplotype were observed between cases and controls. However, examination of KIR in the context of their cognate HLA ligands revealed a strong protective effect for KIR3DL1 in combination with HLA-A and -B alleles bearing the Bw4 motif (P=10-8; odds ratio (OR)=0.60, confidence interval (CI)=0.50-0.71) and the Bw4 ligand alone (P<10-6; OR=0.63, CI=0.53-0.75). The observed effect cannot be explained by either a specific HLA-B allele or by linkage disequilibrium with HLA-DRB1 or HLA-A. The protective effect was observed only in individuals who were not positive for the MS risk allele HLA-DRB1∗15:01 (P<10-6; OR=0.61, CI=0.51-0.74). Our study, the first investigation of KIR and MS in African Americans, confirms and refines previous findings in a European cohort.
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