Knops blood group polymorphism and susceptibility to Mycobacterium tuberculosis infection

BACKGROUND: Complement receptor 1 (CR1) protein carries the Knops blood group antigens and is the receptor for the major ligand involved in Mycobacterium tuberculosis (Mtb) adhesion to macrophages. Erythrocyte CR1 binds immune complexes (ICs) formed during Mtb invasion, facilitating their clearance by the host immune system. The occurrence of specific Knops blood group genotypes among African populations was investigated to evaluate their impact on resistance or susceptibility to Mtb infection. STUDY DESIGN AND METHODS: The distribution of the Knops blood group genotypes (McC and Sl) was compared between tuberculosis (TB) patients with confirmed diagnosis of Mtb in isolates and negative controls. Conditional logistic regression was used to access the association between genotypes distribution and susceptibility to Mtb infection. RESULTS: At the McC locus, individuals heterozygous (McCa/McCb) were more resistant to Mtb infection (odds ratio [OR], 0.42; 95% confidence interval [CI], 0.22-0.81; p = 0.007). Although less significant, a similar effect was conferred by Sl1/Sl2 genotype (OR, 0.05; 95% CI, 0.28-0.9; p = 0.02). This protective effect was maintained among individuals presenting the McCb/Sl2 haplotype (OR, 0.25; 95% CI, 0.08-0.74; p = 0.008). CONCLUSION: Acquisition of McCb and Sl2 alleles among African population is correlated with resistance to Mtb infection, adding this bacterium to the list of mechanisms underlying the selection of the Knops blood group polymorphism among these populations.