Explain what is meant by an antigen and state the difference between self antigens and non-self antigens
Explain what is meant by an antigen and state the difference between self antigens and non-self antigens
Answer
An antigen is any substance that can trigger an immune response in the body. Antigens are typically foreign molecules, such as proteins or polysaccharides, found on the surface of pathogens (like bacteria, viruses, fungi, and parasites), as well as on the surfaces of non-infectious substances (like pollen, food, and transplanted tissues).
Types of Antigens
- Non-Self Antigens: These are foreign antigens that originate from outside the body. They can include:
- Pathogens: Bacteria, viruses, and parasites that invade the body.
- Toxins: Harmful substances produced by organisms (e.g., botulinum toxin).
- Allergens: Substances that provoke allergic reactions (e.g., pollen, pet dander).
- Transplanted Tissues: Organs or cells from another individual (e.g., transplanted organs).
Non-self antigens are recognized by the immune system as foreign, prompting an immune response to neutralize or eliminate them.
- Self Antigens: These are molecules produced by the body that are recognized as part of the organism. They include:
- Normal Body Proteins: Such as proteins found on the surface of cells or within tissues (e.g., blood group antigens).
- Cellular Components: Molecules that play roles in normal physiological processes.
Self antigens are typically not attacked by the immune system due to a process called tolerance, which ensures that the immune system does not mount a response against the body’s own cells and tissues.
Key Differences Between Self Antigens and Non-Self Antigens
| Feature | Self Antigens | Non-Self Antigens |
|---|---|---|
| Origin | Produced by the body (endogenous) | Originates from outside the body (exogenous) |
| Immune Response | Usually not targeted by the immune system (tolerated) | Recognized as foreign, prompting an immune response |
| Examples | Proteins on healthy cells, blood group antigens | Pathogen proteins, toxins, allergens |
| Role in Disease | Can lead to autoimmune diseases if the immune system mistakenly targets them | Can cause infections or allergic reactions |
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