Some People Never Get Sick. Your Genes May Explain Why.

TLR4 (Toll-like receptor 4) is your immune system’s bacterial sensor. When bacteria or their toxins enter your body, TLR4 proteins on your immune cells recognize them and sound the alarm. This first recognition step triggers the entire immune cascade. Without it, your body doesn’t know a threat is present until the bacteria have already established themselves.

The D299G variant in TLR4, carried by roughly 10% of people with European ancestry, reduces your ability to recognize bacterial lipopolysaccharides (LPS), the toxin on bacterial cell walls. People with this variant have a blunted early bacterial immune response. You might not notice the first 24-48 hours of infection because your immune system is slower to wake up.

This means bacterial infections that others clear quickly can linger in your system. A wound that should feel mildly sore stays uncomfortable longer. A sinus infection that should resolve in a week drags on. You’re not immunocompromised, but your early warning system is muted.

FUT2 determines which sugars coat your intestinal lining. This seems minor, but it’s your microbiome’s buffet. The bacteria you carry in your gut feed on these sugars, and certain strains provide immune protection. FUT2 decides which protective bacteria species can thrive in your gut.

Roughly 40-50% of people carry the non-secretor variant (rs602662) of FUT2, which changes the sugar coating and shifts your entire gut bacteria composition. Non-secretors tend to carry fewer of the protective Faecalibacterium and Roseburia species that produce short-chain fatty acids, the metabolites your immune system depends on. These bacteria are like an immune militia; they train your gut lining to recognize threats.

Without them, your intestinal barrier is less trained. Infections that others fight off in your gut lining progress deeper. You catch more gut infections, and respiratory infections are more likely to occur because 70% of immune training happens in your gut. You might notice more frequent mild stomach upset or diarrhea when exposed to pathogens.

VDR (vitamin D receptor) is the lock that vitamin D fits into. You can consume vitamin D, but if your VDR gene has certain variants, the vitamin D can’t unlock the immune-training signals it carries. VDR is expressed heavily in immune cells, and activated vitamin D tells these cells how to respond appropriately.

The Fok1 variant (rs2228570), present in roughly 50% of the population in the tt genotype, produces a longer, slightly less efficient VDR protein. People with the tt genotype need higher vitamin D levels to achieve the same immune signaling as those with shorter VDR proteins. You might be taking vitamin D, have normal blood levels, and still have cells that aren’t receiving the signal.

This is especially obvious in winter. Shorter days mean less sun exposure and lower vitamin D production. With a VDR variant that’s less responsive, your immune cells don’t get the maturation signal they need. You catch more infections in winter, or you notice your recovery is slower when you’re deficient.

HLA genes are your immune system’s presentation system. When your immune cells kill an infected cell, they need to display pieces of the invader to other immune cells as proof of the threat. HLA-DQ2 is one of the ways your cells show these pieces. It’s like holding up a wanted poster so other immune cells know what to look for.

HLA-DQ2 is carried by roughly 25-30% of people with European ancestry. People with this variant can present certain bacterial and viral antigens very effectively to their immune system, triggering faster recognition and response. This is why HLA-DQ2 carriers often have strong natural immunity to certain pathogens.

But there’s a trade-off. HLA-DQ2 is also the gene that, if dysregulated, drives celiac disease and increases risk for type 1 diabetes and other autoimmune conditions. You might be the person who never catches a cold but has to manage a sensitivity to gluten or develop an autoimmune response. Your immune strength is also your vulnerability.

TNF (tumor necrosis factor-alpha) is your immune system’s megaphone. When your body detects a threat, TNF says “Hey, everyone, we’re under attack.” It’s a critical signal for coordinating immune response. But TNF is so powerful that if it’s turned up too loud, it creates collateral damage.

The -308G>A variant (rs1800629), carried by roughly 30% of the population, increases TNF-alpha production across the board. People with the A allele mount a more aggressive inflammatory response to any immune threat, which speeds pathogen clearance but also increases tissue damage. Your recovery is fast but uncomfortable. What should be a mild cold involves days of severe body aches and fatigue.

You get sick less often, or you recover quickly when you do. But when you’re sick, you’re really sick. The inflammation needed to kill the pathogen is also destroying your own cells. You might develop post-infectious fatigue or joint pain after illnesses that don’t affect others the same way.

IL1B (interleukin-1 beta) is your immune system’s emergency alarm. When a threat is detected, IL1B is released and tells your body “switch to defense mode.” It triggers fever, fatigue, and inflammation. It’s the reason you feel sick when you have an infection; that feeling is IL1B coordinating the immune response.

The rs16944 variant, present in roughly 35-40% of the population, increases IL1B production. People with this variant produce more IL1B per immune trigger, meaning they mount a faster and more aggressive inflammatory response to infection. Your immune system responds decisively.

But this comes with a cost. You feel sicker when you’re sick. Fever is higher, aches are more intense, and fatigue is profound because more IL1B is being produced. You clear infections quickly, but the symptom experience is rough. Some people with elevated IL1B also struggle with chronic low-grade inflammation even when not acutely infected, leading to persistent fatigue or joint discomfort.