Antigens

Definition

Antigens are molecules or molecular structures that are recognized by the immune system as foreign and can trigger an immune response. They can be found on the surface of pathogens like bacteria and viruses, or even on infected cells. Understanding antigens is crucial for grasping how adaptive immunity functions, as they play a key role in the activation of lymphocytes and the production of antibodies.

5 Must Know Facts For Your Next Test

1. Antigens can be proteins, polysaccharides, lipids, or nucleic acids, and they can originate from various sources including pathogens, allergens, and even transplanted tissues.
2. The immune system distinguishes between self-antigens (molecules from the body) and non-self-antigens (foreign molecules), which helps prevent autoimmune diseases.
3. Each antigen can have multiple epitopes, which are specific sites on the antigen that antibodies or T-cell receptors recognize and bind to.
4. Vaccination works by exposing the immune system to a harmless form of an antigen, prompting it to produce a response that prepares the body for future encounters with the actual pathogen.
5. Some antigens can change their structure over time, such as in the case of viruses that mutate, making it difficult for the immune system to recognize them after an initial infection.

Review Questions

• How do antigens trigger an immune response in the body?
  • When antigens enter the body, they are detected by lymphocytes, particularly B cells and T cells. This recognition leads to the activation of these immune cells. B cells produce antibodies that specifically target and neutralize the antigen, while T cells may directly kill infected cells or help orchestrate a broader immune response. This process is essential for developing adaptive immunity, allowing the body to remember and respond more effectively to future encounters with the same pathogen.
• Discuss the relationship between antigens and the concepts of immunogenicity and antibody specificity.
  • Immunogenicity refers to how well an antigen can provoke an immune response. Not all antigens are equally immunogenic; factors like size, complexity, and how they are presented influence this ability. Antibody specificity comes into play as antibodies are produced to bind uniquely to specific epitopes on an antigen. This specificity allows for a targeted immune response against pathogens while sparing the body’s own cells.
• Evaluate how changes in antigen structure affect vaccine efficacy and disease outbreaks.
  • Changes in antigen structure, such as mutations in viral proteins, can significantly impact vaccine efficacy. If a virus alters its surface antigens through mutations, it may evade recognition by antibodies generated from previous infections or vaccinations. This phenomenon is seen with influenza viruses and can lead to disease outbreaks despite existing vaccines. Understanding these changes is crucial for vaccine development and public health strategies to prevent epidemics.

Related terms

Antibodies:

Proteins produced by B cells that specifically bind to antigens, neutralizing pathogens or marking them for destruction.

Lymphocytes: A type of white blood cell, including B cells and T cells, that is central to the adaptive immune response and plays a vital role in recognizing antigens.

Immunogenicity: The ability of an antigen to provoke an immune response, influenced by its nature, size, and the context in which it is presented.