Genetic association studies have identified the GTF2I-NCF1 intergenic region on chromosome 7 as a significant susceptibility locus for various autoimmune disorders, including primary Sjögren’s syndrome (pSS) (1, 2), systemic lupus erythematosus (SLE) (3, 4), rheumatoid arthritis (5), systemic sclerosis (SSc) (6), and neuromyelitis optica spectrum disorder (NMOSD) (7, 8). In 2017, the causal polymorphism within this susceptibility locus was pinpointed as the neutrophil cytosolic factor 1 (NCF1) rs201802880 G>A variant. This missense mutation results in an amino acid substitution from arginine (Arg) to histidine (His) at position 90 (9, 10). Beyond its association with disease susceptibility, the NCF1 Arg90His variant has been linked to various clinical and immunological features in SLE. These include an earlier age at diagnosis, presence of anti-beta2 glycoprotein I and anticardiolipin antibodies, increased formation of neutrophil extracellular traps (NETs), elevated serum interferon activity, and impaired macrophage efferocytosis (9–12). This association is further supported by experimental data from NCF1-His90 knock-in (KI) mice, which exhibit reduced oxidative burst, diminished macrophage efferocytosis, splenomegaly, increased type I interferon (IFN-I) scores, and higher levels of plasma cells, as well as enhanced Pristane-induced kidney disease compared to wild-type littermates (11).

The NCF1 Arg90 residue is evolutionarily conserved within the p47phox subunit of the phagocyte NADPH oxidase complex. The frequency of the NCF1 rs201802880 A allele varies significantly globally, being less than 0.5% in Caucasian populations, while exceeding 15% in East Asian groups such as Chinese, Japanese, and Korean populations (13). Despite its association with autoimmune disorders, including those linked to infertility and pregnancy loss due to autoantibodies such as anti-beta2 glycoprotein I and anticardiolipin antibodies (14, 15), the variant persists in human populations. This suggests that the NCF1 Arg90His variant may confer an evolutionary advantage, possibly by offering protection against infectious diseases. Indeed, neutrophils with the homozygous AA genotype demonstrate markedly reduced production of reactive oxygen species (ROS) compared to those with GG or GA genotypes (9, 12). Consistent with this, splenocytes from NCF1-His90 KI mice show a reduced capacity for ROS generation (11). Considering the crucial role of ROS in the pathogenesis of tuberculosis (TB) (16), a contagious disease caused by infection with Mycobacterium tuberculosis (Mtb) bacteria and coexisted with human for more than 40,000 years history (17), we hypothesize that the homozygous AA genotype may confer resistance to TB. This study aims to investigate the relationship between the NCF1 Arg90His variation and susceptibility to tuberculosis.

In this study, we investigated the association between the autoimmune disease-causal variant NCF1 rs201802880 A and tuberculosis, a persistent global infectious disease. Our findings suggest that the AA genotype of the NCF1 rs201802880 polymorphism is associated with a protective effect against active TB in women. Furthermore, the AA genotype correlates with reduced levels of white blood cells and neutrophils in healthy individuals. To date, three genome-wide association studies (GWAS) have been conducted to investigate TB susceptibility in Chinese populations, identifying more than ten genetic loci associated with the disease (19–21). However, the genetic region encompassing the NCF1 gene on chromosome 7 has not been identified as a susceptibility locus for TB. This discrepancy may be attributed to the fact that all prior GWAS analyses were based solely on allele frequencies and did not incorporate stratified analyses by sex (19–21). Given that only the NCF1 AA genotype, rather than the NCF1 A allele, is associated with TB in women, it is unsurprising that this genetic association was not detected in previous studies.

The NCF1 rs201802880 A variant, while conferring protection against TB, is associated with an increased susceptibility to various autoimmune disorders, exemplifying evolutionary trade-offs (22). Throughout human history, our immune system has evolved under the selective pressure of infectious diseases such as TB, which posed significant threats to survival (23). Consequently, genetic variants that enhanced resistance to infections were positively selected. In modern contexts, where infectious diseases are less prevalent, these same variants may lead to overactive immune responses and contribute to autoimmune disorders (24).

Notably, the AA genotype of NCF1 rs201802880, which confers protection against TB in women, is linked to decreased circulating neutrophil levels in healthy individuals. This decrease is more pronounced in women than in men. Neutrophils, the most abundant leukocytes in the blood, play a crucial role in the early immune response to Mtb infection (25). In both human TB and animal models, lung disease manifestations are characterized by neutrophilic inflammation (25, 26), highlighting the critical role of neutrophils in TB pathogenesis.

Neutrophils are thought to play a dual role in the development of TB (27). On one hand, they are highly efficient pathogen-killing cells, employing both direct and indirect mechanisms to contribute significantly to the clearance of Mtb infection. On the other hand, neutrophils have been implicated in promoting Mtb growth and facilitating TB progression. For instance, studies have demonstrated that the risk of TB infection is inversely and independently associated with peripheral blood neutrophil count (28). Additionally, CXCL5 deficiency in murine TB models results in resistance to Mtb infection, attributed to impaired neutrophil recruitment from the bloodstream (29). Thus, it is plausible that the NCF1 rs201802880 AA genotype may confers protection against TB, at least in part, by reducing circulating neutrophil levels.

Both human studies and animal experiments have demonstrated that the NCF1 rs201802880 AA genotype results in reduced ROS production in neutrophils (9, 11, 12). While ROS are essential for neutrophil-mediated elimination of Mtb (30), pathogenic Mtb strains can exploit ROS to enhance their survival (31). For instance, it has been observed that virulent Mtb can persist within human neutrophils despite their rapid activation. This survival is associated with the necrotic death of infected neutrophils, a process entirely dependent on ROS production (32). Therefore, while a complete deficiency in neutrophil-derived ROS impairs the clearance of Mtb, a moderate reduction in neutrophil ROS production may paradoxically confer resistance to TB development.

Notably, the AA genotype is associated with TB specifically in women, but not in men. This sex-specific association suggests that the effect of the NCF1 variant is more pronounced in females than in males. Experimental evidence from knock-in mice supports this hypothesis, as female mice carrying the NCF1 AA genotype exhibit splenomegaly, increased IFN scores, the development of autoantibodies, and lupus-like kidney disease following pristane injection. In contrast, male mice with the same genotype show no evidence of autoimmune disease manifestation (11). The present study further supports this notion, as the decrease in circulating neutrophil levels associated with the AA genotype is more pronounced in women than in men.

Based on these findings, we propose a hypothetical mechanism for the protective effect of the NCF1 rs201802880 AA genotype against TB infection in women. The AA genotype may lead to lower circulating neutrophil levels, thereby impairing neutrophil recruitment to the lung and reducing the transition from Mtb infection to active TB and subsequent neutrophil-mediated tissue damage. Additionally, decreased ROS production in neutrophils may prevent Mtb-triggered ROS-dependent necrotic cell death and facilitate bacterial elimination. It is important to note that this is a simplified model, and other mechanisms involving various immune cells, such as macrophages and dendritic cells, and their dysregulation may also contribute to the observed protective effect against TB (9, 11, 12). For instance, the NCF1 variant may contribute to TB development by affecting the function of antigen-presenting cells. Evidence indicates that NADPH oxidase regulates the activity of cysteine cathepsins by modulating the lumenal redox potential, thereby influencing the production of the MHC II repertoire. This, in turn, impacts antigen presentation and CD4+ T cell-mediated immunity (33, 34). Therefore, it is plausible that the NCF1 AA genotype, which impairs ROS production, may alter the presentation of Mtb antigens to CD4⁺ T cells. Given the pivotal role of CD4⁺ T cells in controlling Mtb infection (35), it is reasonable to propose that the NCF1 variant confers resistance to TB in women by modulating antigen presentation.

This study has two main limitations. Firstly, the association between the NCF1 rs201802880 polymorphism was examined in a single case-control study, and the lack of replication compromises the robustness of the findings. Secondly, although the sample size is substantial, it may still be insufficient for stratified analyses. For example, examining associations between the NCF1 rs201802880 polymorphism and clinical features of TB in subgroups with relatively small sample sizes may reduce statistical power. Therefore, further validation in independent case-control studies with larger sample sizes is warranted.

In conclusion, this study is the first to demonstrate that the autoimmune disease-causal NCF1 variant is associated with a protective effect against TB infection. This finding exemplifies the evolutionary trade-offs where genetic variations that were positively selected for protection against infectious diseases may also increase the risk of autoimmune disorders.