Core Framework & Diagram Why Does the Immune System Attack Itself?
July 28, 20261 Min Read Rheumatoid Arthritis
July 28, 2026When the immune system attacks itself, it's not a 'bug' — it's a well-designed system simultaneously overwhelmed by multiple factors
—— Genetics, infection, hormones, stress — each is one piece of the puzzle.
I. Lock one: genetics — who is born 'more prone to going off course'
Autoimmune diseases have clear genetic backgrounds, but they're not single-gene inheritance. They involve cumulative small variations in dozens to hundreds of genes. HLA genes are the most impactful category — HLA genes encode MHC molecules, determining which types of protein fragments your immune system is best at presenting, and how intense the attack is when a self-protein is 'mistakenly presented.' HLA-DR4 is highly correlated with rheumatoid arthritis; carriers have four to five times normal disease risk. HLA-B27 is strongly associated with ankylosing spondylitis; carriers have ninety to one hundred times normal disease risk. HLA-DR3/DR2 is correlated with lupus; dual-gene carriers have significantly elevated lupus risk.
But genetics isn't destiny. Identical twin studies prove this: even with nearly identical genes, if one twin has lupus, the other's disease rate is only twenty-five to fifty percent — not one hundred percent. This means another fifty to seventy-five percent of disease risk comes from factors beyond genetics. This number is both encouraging (genetics isn't fate) and sobering (environment and lifestyle have more impact than many people assume). Understanding genetic risk's value isn't to create fatalism of 'it's all predetermined' — it's to know that if you have family history, you need to pay more attention to controllable risk factors.
2. Lock two: environmental triggers — the hand that pulls the trigger
Epstein-Barr virus (EBV) is currently the environmental autoimmune trigger with the most substantial evidence. A 2022 Science study covering 1.5 million military records found that EBV-infected individuals developed multiple sclerosis at thirty-two times the rate of uninfected individuals — one of the strongest single infection-autoimmune disease association evidences to date. In lupus, EBV viral protein (EBNA-1) and lupus self-antigen (Sm protein) share molecular mimicry relationships. The proportion of EBV-positive cases among rheumatoid arthritis patients is also significantly higher than in the general population.
UV radiation is the most clearly established environmental inducer of lupus: UV directly damages skin cell DNA, exposing nuclear proteins (like dsDNA and histones) to the extracellular space — and these proteins are the primary targets of lupus autoantibodies.
Gut microbiome dysbiosis is another increasingly studied environmental factor. Rheumatoid arthritis patients show significantly reduced Faecalibacterium prausnitzii in their intestines, while the proportion of Porphyromonas gingivalis — a periodontal pathogen — is elevated. P. gingivalis secretes enzymes that 'citrullinate' host proteins, and this is precisely the target of rheumatoid arthritis's most specific autoantibodies. This causal chain from periodontal disease to rheumatoid arthritis is one of the most important recent discoveries in autoimmune disease etiology research.
3. Lock three: immune regulation failure — brakes failing
Estrogen is an immune 'accelerator': it enhances B cells' antibody-producing capacity, promotes Th1-type inflammatory responses, and simultaneously reduces activation-induced cell apoptosis. This explains why autoimmune diseases are more prevalent in women, why post-pregnancy (sudden estrogen drop) or postpartum and perimenopause (sharp hormonal fluctuations) are peak periods for autoimmune 'eruption.' Estrogen's impact on immunity also explains why, with the same genetic background, women more easily convert susceptibility into actual autoimmune disease — hormones provide more opportunities for opening that 'third lock.'
Chronic stress's role is equally important: long-term chronic stress, by chronically elevating cortisol, causes immune system 'resistance' to cortisol to increase. The result is that inflammatory cytokines (IL-6, TNF-α) are no longer effectively regulated by cortisol, chronic low-grade inflammation persists, and Treg function is simultaneously suppressed. A 2006 JAMA study found that veterans diagnosed with post-traumatic stress disorder (PTSD) had significantly higher autoimmune disease rates than their same-age peers. This isn't just a statistical association — it demonstrates that psychological trauma, through real immunological mechanisms, can become an autoimmune trigger.
4. Randomness — the fifty percent you can't control
Even after understanding all the mechanisms of genetics, environment, hormones, and Treg function, there remains one unsettling fact: a substantial portion of autoimmune disease onset is 'random' — referring to random recombination and random mutations during immune cell development. T cell receptor and B cell receptor diversity is generated through random gene rearrangement. This random process occasionally produces high-affinity self-reactive cells, and whether these cells are cleared by thymic and peripheral tolerance mechanisms also has some randomness.
This randomness explains why identical twins with 'completely identical genes plus completely identical environments' still only have twenty-five to fifty percent concordance rates. For patients, this randomness has one important implication: developing autoimmune disease is not your 'fault.' Genetics, environment, hormones, randomness — none of these are entirely under your control. What you can do is reduce the risk factors you can reduce, and seek medical care early when symptoms appear.
5. What you can do — specific strategies to lower controllable risk
Not smoking is the single most important controllable factor: smoking is an independent risk factor for rheumatoid arthritis, lupus, and multiple sclerosis, and has synergistic effects with HLA-DR4 genetic risk — smoking carriers of the genetic risk have over forty times the rheumatoid arthritis rate of non-smoking non-carriers. Quitting smoking's benefit is especially significant for those with family history.
Maintaining healthy vitamin D levels: vitamin D deficiency is associated with higher rates of multiple sclerosis, type 1 diabetes, rheumatoid arthritis, lupus, and other autoimmune diseases. Northern latitude regions have higher vitamin D deficiency rates, partly explaining autoimmune disease geographic distribution patterns. Aim to maintain serum 25-OH-D in the range of 50–125 nmol/L; supplement vitamin D3 if needed.
Managing chronic stress — not eliminating stress, but preventing chronic over-activation of the HPA axis through regular exercise, adequate sleep, and evidence-supported mindfulness stress reduction methods.
Paying attention to gut health: diverse plant-based diets and reduced ultra-processed food consumption helps maintain gut microbiome diversity.
Early screening for those with family history: antinuclear antibody (ANA), anti-CCP antibody (rheumatoid), thyroid antibodies (Hashimoto's), and similar markers can detect abnormalities years before symptoms appear.
6. The boundary of 'autoimmunity': what we still don't fully understand
Even with deep understanding of autoimmunity, large numbers of unanswered questions remain. Why do two people with identical HLA-DR4 genes — one develop rheumatoid, the other remain disease-free? Why do certain infections trigger certain specific autoimmune diseases rather than others? Why do autoimmune diseases often come in 'clusters' — one person might simultaneously have Hashimoto's thyroiditis and rheumatoid arthritis, but not type 1 diabetes and ankylosing spondylitis?
Answers to these questions are still being researched. Single-cell sequencing technology now allows researchers to precisely analyze 'which cells are doing what' in each autoimmune disease. Large-scale genomics research continues finding more autoimmune-associated genetic variants. Gut microbiome and exposome research systematically maps environmental risk profiles for autoimmunity. These efforts will ultimately deliver more precise prediction tools, earlier intervention windows, and individualized prevention strategies based on specific genetic backgrounds and triggering mechanisms.
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