What you carry at this position in your DNA and what research says about it.
Immune Defense and Gut Health: 6/10 evidence, 31 publications.
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Sample genotype (not yours): T/T
Stronger Immune Defense and Lower Infection Risk
This genotype is associated with enhanced protection against tuberculosis, cytomegalovirus, and post-infectious irritable bowel syndrome. It also correlates with a better response to certain anti-inflammatory medications.
What this genotype means: Lower risk of tuberculosis and CMV infections; Reduced risk of post-infectious IBS; Better response to TNF-alpha inhibitors.
Sample genotype (not yours): C/C
Higher Infection Risk and Poorer Drug Response
This genotype is associated with an increased susceptibility to tuberculosis, cytomegalovirus, malaria, and post-infectious IBS, alongside a poorer response to anti-inflammatory drugs.
What this genotype means: Increased risk of tuberculosis, CMV, and malaria; Higher risk of post-infectious IBS; Poorer response to TNF-alpha inhibitors.
Sample genotype (not yours): T/C
Moderate Infection Risk and Better Drug Response
This genotype is linked to an increased susceptibility to tuberculosis, cytomegalovirus, and post-infectious IBS. However, it also correlates with a more favorable response to anti-inflammatory therapies.
What this genotype means: Increased susceptibility to tuberculosis and CMV; Higher risk of post-infectious IBS; Elevated risk of anti-TB drug liver injury.
Gene function and biological role
Gene Function: TLR9 encodes toll-like receptor 9, a critical component of the innate immune system that detects foreign DNA. It specifically recognizes unmethylated CpG motifs commonly found in bacterial and viral genomes. Upon activation, this receptor triggers inflammatory signaling pathways to help clear the invading pathogen. Proper functioning of this pathway is essential for defense against intracellular infections like tuberculosis and cytomegalovirus.
Variant Impact: An intronic change in the TLR9 gene, rs352139 influences receptor expression levels. Alterations in TLR9 expression can significantly impact how the immune system responds to pathogens. This specific genetic variation has been linked to altered susceptibility to several infectious diseases. It also plays a role in modulating inflammatory responses in the gut and other tissues.
Key Insight: This variant acts as a genetic double-edged sword, where the same allele that protects against major infections like tuberculosis also increases the risk of liver injury during its treatment.
Location: TLR9. Chromosome 3 · 3p21.2 · 52.2 Mb
Estimated prevalence by population
Global 21.1%; European 20.4%; African 17.8%; East Asian 36.7%; South Asian 33.5%; Americas 20.9%; Ashkenazi 19.8%; Finnish 27.0%; Middle Eastern 20.8%; Amish 14.9%.
Estimated TT genotype frequency.
Global 49.3%; European 49.5%; African 48.8%; East Asian 47.8%; South Asian 48.8%; Americas 49.6%; Ashkenazi 49.4%; Finnish 49.9%; Middle Eastern 49.6%; Amish 47.4%.
Estimated TC genotype frequency.
Global 29.6%; European 30.0%; African 33.4%; East Asian 15.5%; South Asian 17.8%; Americas 29.5%; Ashkenazi 30.7%; Finnish 23.1%; Middle Eastern 29.6%; Amish 37.7%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Immunity & Inflammation
Infection Susceptibility & Resistance
Tuberculosis. Evidence: 4/10. Source: PMID 25948535. Lower Risk.
CMV Infection Risk. Evidence: 3/10. Source: PMID 27105145. Lower Risk.
Malaria Susceptibility. Evidence: 4/10. Source: PMID 22594374. Typical Risk.
Organ Systems
Digestive & Gut Disorders
Post-Infectious IBS. Evidence: 3/10. Source: PMID 20044998. Lower Risk.
Pharmacogenomics
Immunosuppressant & Biologic Response
Anti-TNF Drug Response. Evidence: 6/10. Source: PMID 34635730. Stronger Response.
Antimicrobial & Antiviral Response
Tuberculosis Drug Liver Injury. Evidence: 5/10. Source: PMID 39263813. Increased Risk.
Showing effects for C/C genotype
Tuberculosis. Evidence: 4/10. Source: PMID 25948535. Increased Risk.
CMV Infection Risk. Evidence: 3/10. Source: PMID 27105145. Increased Risk.
Malaria Susceptibility. Evidence: 4/10. Source: PMID 22594374. ~4.8x Higher Risk.
Post-Infectious IBS. Evidence: 3/10. Source: PMID 20044998. Increased Risk.
Anti-TNF Drug Response. Evidence: 6/10. Source: PMID 34635730. Poorer Response.
Tuberculosis Drug Liver Injury. Evidence: 5/10. Source: PMID 39263813. Typical Risk.
Showing effects for T/C genotype
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Stronger immune defense helps protect against several common intracellular pathogens. Research indicates that carrying two copies of the T allele is associated with a lower risk of developing active pulmonary tuberculosis. This genotype also provides protection against cytomegalovirus (CMV) infections, particularly in transplant recipients. Additionally, the risk of developing post-infectious irritable bowel syndrome (PI-IBS) following a gut infection is significantly reduced. When treating autoimmune conditions, this genetic profile is linked to a more favorable response to TNF-alpha inhibitors like adalimumab and infliximab. However, there is an increased likelihood of experiencing drug-induced liver injury if undergoing standard tuberculosis therapy with isoniazid or ethambutol. Maintaining overall immune health through balanced nutrition and routine medical care is generally recommended.
Lower risk of tuberculosis and CMV infections; Reduced risk of post-infectious IBS; Better response to TNF-alpha inhibitors.
Sample genotype: CC (Homozygous)
Reduced expression of this immune receptor is linked to higher susceptibility to multiple infectious diseases. Carrying two copies of the C allele is associated with an increased risk of active pulmonary tuberculosis. This genotype also elevates the risk of cytomegalovirus (CMV) infection, particularly in transplant patients. In addition, there is a higher likelihood of developing post-infectious irritable bowel syndrome (PI-IBS) after a gastrointestinal infection. Susceptibility to symptomatic malaria and higher parasite loads have also been observed with this genetic profile. Unlike carriers of the T allele, this genotype is associated with a poorer response to TNF-alpha inhibitor therapies for autoimmune conditions. Conversely, the risk of drug-induced liver injury during standard tuberculosis therapy is not elevated. Supporting the immune system through healthy lifestyle choices remains highly beneficial.
Increased risk of tuberculosis, CMV, and malaria; Higher risk of post-infectious IBS; Poorer response to TNF-alpha inhibitors.
Sample genotype: TC (Heterozygous)
Altered immune receptor expression may increase vulnerability to certain bacterial and viral infections. Carrying one copy of the C allele is associated with a higher susceptibility to active pulmonary tuberculosis. This genetic profile also correlates with an elevated risk of cytomegalovirus (CMV) infection, especially under immunosuppressed conditions. Following bacterial gastroenteritis, there is a higher likelihood of developing chronic post-infectious irritable bowel syndrome (PI-IBS). On the positive side, this genotype is associated with a better therapeutic response to TNF-alpha inhibitors when treating inflammatory diseases. However, if tuberculosis treatment is required, there is an increased risk of experiencing drug-induced liver injury from medications like isoniazid. Monitoring liver enzymes during such therapies is often a standard clinical precaution.
Increased susceptibility to tuberculosis and CMV; Higher risk of post-infectious IBS; Elevated risk of anti-TB drug liver injury.
Variants with shared genetic architecture
rs187084 · TLR9 Gene · Chr 3 · Autoimmune and Obesity Risk
rs352140 · TLR9 Gene · Chr 3 · Lupus and Autoimmune Risk
rs5743836 · TLR9 Gene · Chr 3 · Immune System Activity
Content updated August 2026.
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