Antigen (Ag)

Antigen (Ag)

Definition

An antigen (Ag) is a molecule or substance that can provoke an immune response in the body, specifically by binding to antibodies or T-cell receptors. Antigens can be derived from various sources, including pathogens like bacteria and viruses, as well as non-pathogenic substances such as pollen or transplanted tissues.

Characteristics of Antigens

Types of Antigens:

• Exogenous Antigens: These originate from outside the body, such as pathogens (bacteria, viruses), allergens (pollen), and toxins.
• Endogenous Antigens: These are produced within the body, often as a result of infections or cellular processes.
• Autoantigens: These are self-antigens that can trigger an immune response in autoimmune diseases.
• Tumor Antigens: These are associated with cancer cells and can stimulate an immune response.

Structure:

• Antigens can be proteins, polysaccharides, lipids, or nucleic acids. They often have specific regions known as epitopes that are recognized by antibodies or T-cell receptors.

Immune Response Activation:

• When an antigen enters the body, it is recognized by the immune system. This recognition leads to the activation of lymphocytes (B cells and T cells), which respond by producing antibodies or directly attacking the antigen.

Immunogenicity:

• Not all antigens are equally effective at inducing an immune response; this property is known as immunogenicity. Factors influencing immunogenicity include the size, complexity, and foreignness of the antigen.

Vaccines:

• Vaccines often contain antigens in a form that stimulates an immune response without causing disease. This helps the body develop memory against specific pathogens.

Conclusion

Antigens play a crucial role in the immune system by triggering responses that help protect the body from infections and diseases. Understanding antigens is fundamental in immunology, vaccine development, and therapeutic interventions.

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References

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2. Merriam-Webster Dictionary. (2024). Antigen Definition & Meaning. Retrieved from Merriam-Webster DOI: 10.1016/j.jpsychores.2009.02.001.
3. BYJU’S Biology. (n.d.). What are Antigens? – Definition, Properties, Types, Structure. Retrieved from BYJU’S DOI: 10.3390/cells8020148.
4. Cleveland Clinic. (n.d.). Antigen: What It Is, Function, Types, & Testing. Retrieved from Cleveland Clinic DOI: 10.1007/s12053-017-9571-5.
5. Britannica. (2023). Antigen | Definition, Function, Types, & Facts. Retrieved from Britannica DOI: 10.1016/j.cell.2013.05.029.