Describe active immunity as defence against a pathogen by antibody production in the body

SouravNovember 14, 2024

Answer

Active immunity is a crucial defense mechanism of the immune system that involves the body’s production of antibodies in response to exposure to a pathogen. Here’s a detailed explanation of how active immunity works, focusing on the process of antibody production:

Definition of Active Immunity

Active immunity occurs when an individual’s immune system is exposed to a pathogen or its antigens, leading to the generation of a specific immune response. This type of immunity can develop naturally through infection or artificially through vaccination.

Mechanism of Active Immunity

1. Exposure to Pathogen:
   • When a pathogen (such as a virus or bacterium) enters the body, it triggers an immune response. This can occur through natural infection when the pathogen invades and causes disease or through vaccination, where a weakened or inactive form of the pathogen is introduced to stimulate an immune response without causing disease.
2. Activation of Immune Cells:
   • The presence of the pathogen is detected by antigen-presenting cells (APCs), such as dendritic cells and macrophages. These cells process the antigens from the pathogen and present them on their surface using major histocompatibility complex (MHC) molecules.
   • Helper T cells (CD4+ T cells) recognize these MHC-antigen complexes and become activated. They play a critical role in coordinating the immune response by releasing cytokines that stimulate other immune cells.
3. B Cell Activation and Antibody Production:
   • Once activated, helper T cells interact with B cells that have receptors specific to the same antigen. This interaction stimulates B cells to proliferate and differentiate into two main types:
     • Plasma Cells: These are responsible for producing large quantities of antibodies specific to the pathogen’s antigens. Antibodies are Y-shaped proteins that bind to antigens, neutralizing pathogens or marking them for destruction by other immune cells.
     • Memory B Cells: Some B cells become memory cells that persist long after the initial infection has been cleared. These memory B cells allow for a faster and more robust immune response upon subsequent exposure to the same pathogen.
4. Antibody Function:
   • The antibodies produced by plasma cells circulate in the bloodstream and bind specifically to antigens on pathogens. This binding can neutralize toxins, prevent pathogens from entering host cells, and facilitate their destruction by other immune components, such as phagocytes.
   • The presence of antibodies also enhances opsonization, where pathogens coated with antibodies are more easily recognized and engulfed by phagocytes.
5. Long-term Protection:
   • Active immunity typically provides long-lasting protection against specific pathogens due to the formation of memory B and T cells. If the individual encounters the same pathogen again in the future, these memory cells can quickly activate and produce antibodies, leading to a more rapid and effective immune response.