Genetic Susceptibility to Autoimmune Disease
Certain gene variants raise the odds of autoimmune disease later.
- ~30%: HLA-DQ2/DQ8 carriers (of general population)
- ~3%: Celiac disease penetrance (among HLA carriers)
- ~5–10%: PTPN22 risk allele (population frequency)
- 80+: Autoimmune diseases known (distinct conditions)
HLA genes set the stage
HLA molecules shape which antigens the immune system notices.
Non-HLA risk genes
PTPN22, IL23R, NOD2 variants tune immune cell sensitivity.
Genes load the gun; environment often pulls the trigger.
Susceptibility is not destiny
Most gene carriers never develop autoimmune disease at all.
Increased Intestinal Permeability ("Leaky Gut")
Tight junctions loosen, letting large molecules cross the gut wall.
- 40+: Tight junction proteins (claudins, occludin, ZO-1)
- ↑: Zonulin (key permeability regulator)
- Direct: Gliadin effect (triggers zonulin release)
- ~32 m²: Gut surface area (a tennis court, roughly)
Tight junctions normally seal the gut
A single epithelial layer keeps lumen contents out of circulation.
Zonulin loosens the seal
Zonulin release reversibly opens the paracellular gaps.
Fasano's zonulin model links leaky gut to several autoimmune diseases.
Triggers of permeability
Gliadin, dysbiosis, infection, and stress all raise permeability.
Immune System Exposure to Translocated Antigens
Food and bacterial fragments reach immune cells they should never meet.
- Dense: Lamina propria immune cells (dendritic cells, T cells, macrophages)
- Controlled: Normal antigen sampling (via M cells, Peyer's patches)
- Uncontrolled: Leaky exposure (bypasses normal tolerance)
- Local: Cytokine surge (TNF-α, IL-6, IL-17 rise)
Normal vs. leaky antigen sampling
Regulated sampling teaches tolerance; leaky exposure skips that step.
Dendritic cells present the antigen
Antigen-presenting cells display fragments to nearby T cells.
Chronic exposure keeps local immune cells persistently switched on.
Low-grade inflammation builds
Repeated exposure sustains a low-grade inflammatory state.
Molecular Mimicry — When Antigens Resemble Self
Some microbial or food proteins structurally resemble human tissue proteins.
- GAD65: Classic example (shared with Coxsackievirus)
- Yersinia: Thyroid mimicry (linked to Graves' disease)
- Transglutaminase: Gluten mimicry (celiac cross-reactivity)
- Rare but real: Cross-reactive T cells (shared epitope recognition)
Shared epitopes confuse the immune system
A foreign shape matching a self-protein can fool immune recognition.
Antibodies and T cells cross-react
Antibodies raised against the antigen also bind the self-protein.
Mimicry turns a normal microbial response into a self-attack.
Not every mimic causes disease
Cross-reactivity needs sustained exposure plus genetic susceptibility.
Sustained Autoimmune Activation
Combined genetic risk and chronic exposure drive true autoimmune disease.
- ~5–8%: Autoimmune prevalence (of the population)
- ~78%: Female predominance (of autoimmune patients)
- Documented: Leaky gut in T1D (before disease onset)
- Associated: Leaky gut in RA/MS (active research area)
From cross-reactivity to tissue damage
Activated immune cells now persistently target healthy tissue.
A three-hit hypothesis
Genes, a leaky barrier, and a trigger together enable disease.
The leaky-gut hypothesis is compelling but still not fully proven causal.
Why the barrier matters clinically
Restoring barrier integrity is an active autoimmune therapy target.