Explain that vaccines contain antigens that stimulate immune responses to provide long-term immunity

SouravOctober 30, 2024

Answer

Vaccines are biological preparations designed to provide immunity against specific infectious diseases. They contain antigens, which are substances that stimulate the immune system to recognize and respond to pathogens. Here’s how vaccines work in detail:

1. What Are Antigens?

• Definition: Antigens are molecules or molecular structures that are recognized by the immune system as foreign. They can be proteins, polysaccharides, or other components derived from pathogens (like bacteria or viruses).
• Types of Antigens in Vaccines:
  • Inactivated or Killed Pathogens: Vaccines may contain pathogens that have been killed or inactivated so that they cannot cause disease (e.g., polio vaccine).
  • Live Attenuated Pathogens: Some vaccines contain weakened forms of live pathogens that can still replicate but do not cause disease (e.g., measles, mumps, and rubella (MMR) vaccine).
  • Subunit Vaccines: These contain specific pieces of the pathogen (such as proteins or sugars) that are sufficient to elicit an immune response (e.g., human papillomavirus (HPV) vaccine).
  • mRNA Vaccines: These vaccines use messenger RNA to instruct cells to produce a protein that is an antigen, stimulating an immune response (e.g., Pfizer-BioNTech and Moderna COVID-19 vaccines).

2. Stimulation of Immune Responses

• Immune Activation: When a vaccine is administered, the antigens in the vaccine are recognized by the immune system as foreign. This triggers an immune response that involves several key processes:
  • Antigen Presentation: Antigen-presenting cells (APCs), such as macrophages and dendritic cells, take up the antigens and present them on their surface using Major Histocompatibility Complex (MHC) molecules. This allows T-lymphocytes (T-cells) to recognize and respond to the antigens.
  • T-Cell Activation: T-helper cells (CD4+ T-cells) are activated by recognizing the antigen-MHC complex. Activated T-helper cells secrete cytokines, which help recruit and activate other immune cells, including B-lymphocytes (B-cells).
  • B-Cell Activation: B-cells recognize the antigens directly or receive signals from activated T-helper cells. Once activated, B-cells proliferate and differentiate into plasma cells that produce antibodies specific to the antigens.

3. Production of Antibodies and Memory Cells

• Antibody Production: The plasma cells generated from activated B-cells produce large quantities of antibodies. These antibodies circulate in the bloodstream and bind to the pathogen if it is encountered in the future, neutralizing it and marking it for destruction by other immune cells.
• Memory Cell Formation: In addition to plasma cells, some activated B-cells and T-cells differentiate into memory cells. These cells remain in the body long after the initial immune response has subsided. Memory B-cells can quickly produce antibodies upon re-exposure to the same antigen, while memory T-cells can mount a rapid immune response.

4. Providing Long-Term Immunity

• Rapid Response to Re-exposure: When a vaccinated individual encounters the actual pathogen later, the memory cells are able to recognize the pathogen quickly. This leads to a faster and more robust immune response compared to the primary immune response that occurs during the first exposure.
• Duration of Immunity: Many vaccines provide long-lasting immunity, often for years or even a lifetime. The presence of memory cells ensures that the immune system can respond effectively to future infections.