rs4833095 — TLR1 N248S

TLR1 N248S — A Receptor's Extracellular Domain Under Evolutionary Pressure

Your immune system detects bacterial invaders through a set of sentinel proteins called Toll-like receptors. TLR1 acts as a co-detector for triacylated lipopeptides — the fatty-acid decorated proteins that coat many gram-positive bacteria, mycobacteria, and fungi. It does this not alone, but as an obligate heterodimer with TLR2: TLR1 grasps one of the three lipid chains of the pathogen while TLR2 anchors the complex. The N248S variant sits directly in this extracellular recognition domain, and the serine substitution impairs how efficiently the receptor captures its ligand.

This is the second functional missense variant in TLR1 in the GeneOps database — the other being I602S (rs5743618), which disrupts intracellular trafficking. Whereas I602S prevents TLR1 from ever reaching the cell surface, N248S alters the protein that does reach the surface, weakening the initial contact between receptor and bacterial lipopeptide.

The Mechanism

TLR1's extracellular domain contains a series of leucine-rich repeat (LRR) modules arranged in a horseshoe shape. In the crystal structure of the TLR1-TLR2 heterodimer¹¹ crystal structure of the TLR1-TLR2 heterodimer
Jin et al., 2007; resolved to 2.1 Å showing lipopeptide lodged in a hydrophobic channel in TLR1's LRR domain, position 248 falls within the central LRR region that forms part of the heterodimerization interface between TLR1 and TLR2.

Asparagine at position 248 carries a polar amide side chain capable of hydrogen bonding. The serine substitution (N248S) replaces this with a shorter hydroxyl group, altering the local surface geometry at a region implicated in receptor-receptor contact. Studies of functional outcomes show that this change diminishes TLR1/TLR2 signaling to triacylated lipopeptide stimulation in cellular assays — reduced NF-κB activation and attenuated cytokine production. This includes documented loss-of-function in HMGB1-mediated TLR1–TLR2 signaling²² HMGB1-mediated TLR1–TLR2 signaling
HMGB1 is a damage-associated molecular pattern that activates TLR1/TLR2 as a secondary pathway alongside its RAGE and TLR4 interactions.

Because N248S and I602S (rs5743618) are in linkage disequilibrium — they co-segregate on the same haplotype in most populations — individuals carrying one variant often carry both. The extracellular impairment of N248S and the trafficking impairment of I602S therefore tend to compound on the same chromosome.

The Evidence

Leprosy and mycobacterial disease: Schuring et al. (2009)³³ Schuring et al. (2009)
Polymorphism N248S in the human Toll-like receptor 1 gene is related to leprosy and leprosy reactions. J Infect Dis 199:1816–9 genotyped rs4833095 in a Bangladeshi leprosy cohort and found that the SS homozygous genotype (Ser/Ser, CC on plus strand) was significantly over-represented in leprosy patients vs controls (p=0.012). Heterozygous NS carriers were under-represented (p=0.015), a protective heterozygote effect also seen in I602S data⁴⁴ I602S data. The mechanism is consistent with reduced TLR1 signaling failing to generate the robust mycobacterial response needed for early pathogen control — though the same blunted response can reduce immunopathology in chronic infection.

A sex-stratified Brazilian study by Brito-de-Souza et al. (2018)⁵⁵ Brito-de-Souza et al. (2018)
The TLR1 gene is associated with higher protection from leprosy in women. PLOS One found that the heterozygous C/T genotype was protective specifically in women (OR=0.54, 95% CI 0.32–0.91, p=0.02) but not in men. This sex-specific finding suggests that sex hormones modulate TLR1-dependent immunity, with women gaining a signal-buffering benefit from heterozygosity.

Gram-positive sepsis mortality: In a traumatic-injury cohort study, Wurfel et al.⁶⁶ Wurfel et al.
Toll-like Receptor 1 Polymorphisms and Associated Outcomes in Sepsis Following Traumatic Injury. PMC3686843 found that the Ser248 allele (C on plus strand; G in the coding-strand notation used in that paper) was associated with OR 4.16 (95% CI 1.22–14.19, p=0.023) for in-hospital death from gram-positive sepsis, with 26.3% mortality in GG homozygotes vs 11.3% in AA homozygotes. This large effect size suggests that impaired TLR1 recognition of gram-positive bacterial lipopeptides meaningfully reduces the ability to clear these pathogens when sepsis develops.

Cytokine effects: Dos Santos et al. (2017)⁷⁷ Dos Santos et al. (2017)
Polymorphisms in TLR1, 2 and 4 associated with differential cytokine and chemokine serum production in leprosy patients. PMC5354609 showed that T allele (Asn248) carriers produced significantly higher IL-12p40 and IL-17 compared to CC (Ser/Ser) homozygotes, while MCP-1 was lower in TT homozygotes. This supports the interpretation that Asn248 (T allele) enables more robust Th1 inflammatory signaling, while Ser248 (C allele) blunts it.

IgA nephropathy: In a Chinese Han population, Zhao et al. (2016)⁸⁸ Zhao et al. (2016)
TLR1 polymorphism rs4833095 as a risk factor for IgA nephropathy. PubMed 27806314 found that the T allele (Asn248, full-function form) increased IgA nephropathy risk (OR=1.27, p=0.04). This is the inverse of the infection finding: higher TLR1 activity from Asn248 may drive the excessive mucosal immune activation underlying IgA immune complex deposition in the kidney.

Prostate cancer: A TLR10-TLR1-TLR6 cluster haplotype including rs4833095 was associated with OR 0.55 (95% CI 0.33–0.90) reduced prostate cancer risk in a large US case-control study (1,414 cases, 1,414 controls), though the independent contribution of rs4833095 vs co-inherited variants in this cluster is not resolved.

Practical Implications

The clinical meaning of N248S is shaped by LD with I602S (rs5743618). Individuals who carry the C allele at both variants have additive reductions in TLR1 surface signaling: both the receptor that reaches the surface (N248S impairment) and the total amount of surface receptor (I602S trafficking impairment) are reduced. For most people in low-infection-burden environments, this blunted TLR1 response is largely asymptomatic — the immune system compensates via TLR2/TLR6 (diacylated lipopeptides), TLR4 (LPS), and TLR9 (bacterial DNA).

The actionable context is for individuals with meaningful exposure to gram-positive bacteria or mycobacteria: CC homozygotes have documented vulnerability to worse outcomes in gram-positive sepsis and leprosy-endemic settings. Early antibiotic treatment and infection prevention are the relevant levers.

For TT homozygotes (Asn248/Asn248), the intact TLR1 extracellular domain provides robust bacterial recognition — but the trade-off observed in IgA nephropathy data suggests that excessive TLR1 signaling at mucosal surfaces may contribute to aberrant immune activation in contexts where immune complex deposition matters.

Interactions

N248S is in strong LD with I602S (rs5743618) — both are functional TLR1 missense variants on the same haplotype. Most studies cannot fully disentangle their independent effects. The combined haplotype carrying both Ser248 and Ser602 produces TLR1 with both a weakened extracellular ligand-binding domain and absent cell surface trafficking.

TLR2 (rs5743708) is TLR1's obligate heterodimer partner — variants that reduce TLR2 surface expression would compound N248S impairment. TLR6 (rs5743810) handles the diacylated lipopeptide arm of TLR2-dependent signaling; its function is independent of TLR1 N248S. TLR4 (rs4986790) handles LPS from gram-negative bacteria via a separate receptor complex.