Molecular mimicry

Molecular mimicry is a phenomenon where a foreign antigen shares structural similarities with self-antigens, leading to an immune response that mistakenly targets the body's own tissues. This concept is significant in understanding the pathogenesis of various autoimmune diseases.

Mechanism

Molecular mimicry occurs when pathogen-derived antigens resemble host proteins. The immune system, in its attempt to eliminate the pathogen, may also attack the host tissues that express similar antigens. This can lead to autoimmunity, where the body's immune system attacks its own cells.

T Cell Activation

The activation of T cells is a critical step in the immune response. T cells recognize antigens presented by major histocompatibility complex (MHC) molecules. If a pathogen's antigen mimics a self-antigen, T cells may become activated against both the pathogen and the host tissue.

B Cell Activation

B cells can also contribute to molecular mimicry. When B cells recognize an antigen, they can produce antibodies that may cross-react with self-antigens, leading to tissue damage.

Examples of Diseases

Several autoimmune diseases are thought to be triggered by molecular mimicry:

• Rheumatic fever: Following a Streptococcus pyogenes infection, antibodies against the bacteria may cross-react with heart tissue, leading to inflammation.
• Guillain-Barré syndrome: Often follows a Campylobacter jejuni infection, where antibodies against the bacteria may attack peripheral nerves.
• Multiple sclerosis: Some viral infections are hypothesized to trigger an immune response against myelin, the protective sheath around nerve fibers.

Implications for Treatment

Understanding molecular mimicry can aid in developing treatments for autoimmune diseases. Strategies may include:

• Designing vaccines that avoid cross-reactive epitopes.
• Developing immunotherapies that specifically target pathogenic immune responses without affecting normal immune function.

Related Pages

• Autoimmunity
• Immune system
• Antigen
• Pathogen