MARCO variants are associated with phagocytosis, pulmonary tuberculosis susceptibility and Beijing lineage

Abstract

Macrophage receptor with collagenous structure (MARCO) has an important role in the phagocytosis of Mycobacterium tuberculosis (M. tuberculosis). We hypothesized that MARCO polymorphisms are associated with phagocytosis, tuberculosis (TB) disease susceptibility and presentation, and infecting lineage. We used a human cellular model to examine how MARCO genotype mediates the immune response; a case-control study to investigate tuberculosis host genetic susceptibility; and a host-pathogen genetic analysis to study host-pathogen interactions. Two MARCO heterozygous (AG) genotypes (single-nucleotide polymorphisms rs2278589 and rs6751745) were associated with impaired phagocytosis of M. tuberculosis trehalose 6,6'-dimycolate-cord factor and β-glucan-coated beads in macrophages. The heterozygous genotypes of rs2278589 and rs6751745 were also associated with increased risk of pulmonary TB (PTB; rs2278589, P=0.001, odds ratio (OR)=1.6; rs6751745, P=0.009, OR=1.4), and with severe chest X-ray abnormalities (P=0.007, OR=1.6). These two genotypes were also associated with the Beijing lineage (rs2278589, P=0.001, OR=1.7; rs6751745, P=0.01, OR=1.5). Together, these results suggest that MARCO polymorphisms may regulate phagocytosis of M. tuberculosis and susceptibility and severity of PTB. They also suggest MARCO genotype and Beijing strains may interact to increase the risk of PTB.

Figure 1

Phagocytic ability of macrophages from individuals with different TB phenotypes. Monocyte-derived macrophages from patients at day 7 were treated with Alexa 547-beads coated with either immunoglobulin-G (IgG), trehalose 6,6'-dimycolate (TDM) or β-glucan. Phagocytic ability was determined by the percentage of macrophages with beads in three TB phenotypes (55 TB meningitis, 52 pulmonary TB and 56 latent TB). Bars in plots represent median values. Comparisons across three groups of TB forms or genotypes were performed by using one-way analysis of variance. On these comparisons, P-values >0.05.

Figure 2

Phagocytic ability of macrophages from healthy subjects. Macrophage phagocytosis of beads was assessed according to MARCO SNP genotypes in healthy subjects; (a) rs2278589 (18 GG, 18 AG, 5 AA) and (b) rs6751745 (19 GG, 18 AG, 4 AA). Bars in plots represent median values. Comparisons across three groups of TB forms or genotypes were performed by using one-way analysis of variance, or two groups by using Mann–Whitney U-test.

Figure 3

MARCO polymorphisms and variation in mRNA expression or cytokine production from healthy subjects. (a) mRNA was isolated from monocytes stimulated with Media, LPS at 100 ng ml⁻¹ or M. tuberculosis whole-cell lysate at 5 μg ml⁻¹. MARCO mRNA expression was measured and normalizes to glyceraldehyde-3-phosphate dehydrogenase. (b) Association of MARCO mRNA expression from cells stimulated with M. tuberculosis whole-cell lysate was analyzed with SNPs in MARCO: rs2278589 (4 AA, 12 AG, 15 GG), P=0.068 and rs6751745 (3 AA, 13 AG, 15 GG), P=0.039. (c) Cytokines were measured from monocytes stimulated with media, TDM at 100 μg ml⁻¹ or M. tuberculosis whole-cell lysate at 25 μg ml⁻¹. Cytokines from cells stimulated with TDM (d) or M. tuberculosis whole-cell lysate (e) were analyzed with SNP rs2278589 (4 AA, 12 AG, 15 GG). Cytokines from cells stimulated with TDM (f) or M. tuberculosis whole-cell lysate (g) were analyzed with SNP rs6751745 (3 AA, 13 AG, 15 GG). Data were collected from duplicate samples. Bars in plots represent median values. Comparisons across three genotypes were performed by using one-way analysis of variance.