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[Immunology](https://durgical.com/en/immunology/) · [Autoimmunity](https://durgical.com/en/immunology/#a-autoimmunity)

# Molecular mimicry and post-infectious autoimmunity

- Process

Some germs carry pieces that look like our own tissue. The defence aimed at the germ can then hit the look-alike tissue, weeks after the infection.

Updated 2026-11-01

## Key points

- Mimicry = a microbe antigen resembles a self antigen; cross-reactive immunity attacks the self tissue.
- Rheumatic fever: streptococcal M protein cross-reacts with cardiac myosin (type II).
- Guillain–Barré after Campylobacter jejuni: anti-ganglioside antibodies.
- Reactive arthritis after genital or enteric infection, mostly in HLA-B27 carriers.
- Disease needs a susceptible host; most infected people never develop autoimmunity.

## What it is

Molecular mimicry happens when a microbe shares a sequence or a shape with a host molecule. Antibodies or T cells raised against the microbe cross-react with the self molecule, so autoimmunity can start after the infection has cleared. Mimicry alone is rarely enough: the right genes (often HLA), a strong inflammatory response and other hits decide who gets sick. Rheumatic fever and Guillain–Barré syndrome are the classic examples, and both still matter in Latin America.

## Step by step

- An infection carries an antigen that resembles a self protein or sugar.
- Inflammation activates antigen-presenting cells and breaks the usual tolerance threshold.
- B and T cells against the microbe expand, including clones that also fit the self molecule.
- The microbe is cleared, but the cross-reactive cells and antibodies remain.
- They attack the look-alike tissue: heart valve, nerve, joint or brain, usually weeks later.

## Infections and the autoimmunity that can follow

| Infection | Cross-reaction | Disease | Typical delay |
| --- | --- | --- | --- |
| Streptococcus pyogenes pharyngitis | M protein and group A carbohydrate resemble cardiac myosin and valve proteins | Acute rheumatic fever, rheumatic heart disease, Sydenham chorea | About 2–4 weeks |
| Campylobacter jejuni diarrhea | Bacterial lipo-oligosaccharide resembles nerve gangliosides | Guillain–Barré syndrome (often the axonal form) | 1–3 weeks |
| Chlamydia trachomatis, Salmonella, Shigella, Yersinia, Campylobacter | Proposed cross-reaction in HLA-B27 carriers; mechanism not fully settled | Reactive arthritis (with conjunctivitis or urethritis) | 1–4 weeks |
| Epstein–Barr virus | EBNA-1 resembles lupus Sm antigens and some myelin proteins | Proposed contributor to lupus and multiple sclerosis | Years |

## Clinical notes

- Rheumatic heart disease is still a leading cause of acquired valve disease in young people in Colombia and Latin America; treating strep pharyngitis prevents the first attack.
- Post-streptococcal glomerulonephritis also follows strep infection but is immune-complex (type III) disease, not mimicry; it can follow skin infection too.
- The 2015–2016 Zika epidemic in Colombia brought a rise in Guillain–Barré syndrome; the exact mechanism is still being studied.

## Memory aid

Mistaken identity: the immune system chases the germ's face and later arrests a look-alike neighbour.

## Test yourself

Think of the answer, then tap the question to see it.

## Which streptococcal protein is the classic example of molecular mimicry in rheumatic fever?

The M protein of Streptococcus pyogenes, which resembles cardiac myosin and valve proteins, so the anti-streptococcal response damages the heart.

## Which infection most often precedes Guillain–Barré syndrome, and what is mimicked?

Campylobacter jejuni diarrhea. Its lipo-oligosaccharide looks like gangliosides on peripheral nerves, and the cross-reactive antibodies injure the nerves.

## Why do most people with strep pharyngitis never develop rheumatic fever?

Mimicry needs a susceptible host: genes such as HLA, the strength of the response and other factors decide who crosses the line into autoimmunity.

## Is post-streptococcal glomerulonephritis an example of molecular mimicry?

No. It is mainly immune-complex (type III) injury in the glomeruli, with low C3; rheumatic fever is the mimicry (type II) complication.

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## Related

- [Immune tolerance and how autoimmunity begins](https://durgical.com/en/immunology/immune-tolerance-and-how-autoimmunity-begins/)
- [Type II hypersensitivity (antibody against cells)](https://durgical.com/en/immunology/type-ii-hypersensitivity/)
- [Autoantibodies: the table to know](https://durgical.com/en/immunology/autoantibodies-the-table-to-know/)
- [HLA associations with disease](https://durgical.com/en/immunology/hla-associations-with-disease/)
- [Antigen processing and presentation](https://durgical.com/en/immunology/antigen-processing-and-presentation/)

## Related conditions

- [Rheumatic heart disease](https://durgical.com/en/conditions/rheumatic-heart-disease/)
- [Guillain-Barré syndrome](https://durgical.com/en/conditions/guillain-barre-syndrome/)
- [Streptococcal pharyngitis](https://durgical.com/en/conditions/streptococcal-pharyngitis/)
- [Systemic lupus erythematosus](https://durgical.com/en/conditions/systemic-lupus-erythematosus/)
- [Multiple sclerosis](https://durgical.com/en/conditions/multiple-sclerosis/)
- [Zika virus infection](https://durgical.com/en/conditions/zika-virus-infection/)

## Microorganisms

- [Streptococcus pyogenes](https://durgical.com/en/microbiology/streptococcus-pyogenes/)
- [Campylobacter jejuni](https://durgical.com/en/microbiology/campylobacter-jejuni/)
- [Chlamydia trachomatis](https://durgical.com/en/microbiology/chlamydia-trachomatis/)
- [Non-typhoidal Salmonella](https://durgical.com/en/microbiology/non-typhoidal-salmonella/)
- [Shigella](https://durgical.com/en/microbiology/shigella/)
- [Yersinia](https://durgical.com/en/microbiology/yersinia/)

[← All of immunology](https://durgical.com/en/immunology/)

Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.

Sources: [Molecular mimicry in autoimmunity and vaccinations](https://www.ncbi.nlm.nih.gov/books/NBK459460/) (El Rosario University Press (NCBI Bookshelf), 2013); [Autoimmune responses are directed against self antigens](https://www.ncbi.nlm.nih.gov/books/NBK27155/) (Garland Science (Janeway's Immunobiology, 5th ed., NCBI Bookshelf), 2001).

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