Table of Contents
- Introduction of Active Immunity
- Characteristics of Active Immunity
- Types of Active Immunity
- Mediators of active immunity
- Active Immunity vs. Passive Immunity
- References
Introduction of Active Immunity
- Active immunity develops when the body produces its own antibodies in response to exposure to a pathogen or foreign antigen.
- It provides long-term protection and resistance against infections.
- Active immunity is induced when the immune system responds to a foreign antigen by producing antibodies.
- The immune system recognizes a pathogen, activates immune cells, and generates a defense mechanism against it.
- It can be acquired through clinical or subclinical infection, which refers to previous exposure to an antigen that may or may not have caused noticeable symptoms.
- It can also be induced through immunization by vaccination with live or killed infectious agents or their antigens.
- Exposure to microbial products such as toxins and toxoids can also trigger an immune response.
- The immune system stimulates an immune response against foreign antigens by activating B-cells, which produce antibodies, and T-cells (T-helper and cytotoxic T-cells), which help eliminate infected cells.
- There is an initial lag period before immunity is fully developed, but once established, active immunity provides long-lasting protection.
- The primary immune response may be slow, but memory cells ensure a faster and stronger response against future exposures.
- Active immunity plays a crucial role in protecting individuals from infections and is the foundation of vaccination programs worldwide.
Characteristics of Active Immunity
- Active immunity requires exposure to a pathogen or its antigen.
- This exposure stimulates the production of antibodies, which mark infected cells for destruction by lymphocytes.
- Cells involved in active immunity include T-cells (cytotoxic T cells, helper T cells, memory T cells, and suppressor T cells), B-cells (memory B cells and plasma cells), and antigen-presenting cells (B cells, dendritic cells, and macrophages).
- There is a delay between exposure to the antigen and the development of immunity.
- The first exposure triggers a primary immune response, which takes time to develop.
- Upon subsequent exposure, the immune system mounts a secondary response, which is much faster and stronger.
- Active immunity provides long-term protection, often lasting a lifetime.
- Some potential side effects of active immunity include autoimmune diseases and allergic reactions in certain cases.
Types of Active Immunity
A. Natural active immunity
- Natural active immunity is acquired when an individual is exposed to a pathogen either clinically (with symptoms) or subclinically (without noticeable symptoms).
- Exposure to a live pathogen leads to infection, triggering the immune system to develop a long-term immune response.
- When a microbe bypasses the body's primary defenses, such as the skin or mucous membranes, it activates B-cells, which produce antibodies to fight the infection.
- The adaptive immune response takes days or weeks to develop but can provide long-lasting or lifelong immunity.
- For example, individuals infected with the hepatitis A virus (HAV) and subsequently recovering develop a natural active immune response, often leading to lifelong immunity.
B. Artificial active immunity
- Artificial active immunity is induced through vaccination, where an antigen is introduced into the body to stimulate an immune response.
- The administration of vaccines, such as the hepatitis A vaccine, triggers an immune response that provides long-term or lifelong protection against the disease.
- Vaccination is a deliberate process that introduces a harmless form of an antigen (derived from a pathogen) to activate the immune system without causing disease.
- Immunizations are highly effective because they leverage the immune system’s natural specificity and ability to form memory cells.
- The principle behind vaccination is to stimulate protective immunity while avoiding the harmful effects of the actual pathogen.
- Artificial active immunity is achieved through various vaccines, which may be live vaccines, killed vaccines, or vaccines containing bacterial products.
Mediators of active immunity
Active immunity is mediated by humoral immunity and cell-mediated immunity, both of which play crucial roles in eliminating pathogens.
Humoral immunity
- Mediated by antibodies found in blood and mucosal secretions.
- B-cell plasma cells secrete antibodies that recognize microbial antigens, neutralize their infectivity, and mark them for elimination.
- This type of immunity is the primary defense against extracellular pathogens.
Cell-mediated immunity
- Mediated by T-helper (TH) cells and cytotoxic T lymphocytes (CTLs).
- T-helper cells secrete cytokines that activate phagocytic cells, enhancing their ability to engulf and destroy pathogens.
- Cytotoxic T lymphocytes (CTLs) play a key role in killing virus-infected cells and tumor cells by targeting altered self-cells.
- This immune response is particularly important against intracellular bacterial and protozoal infections.
Active Immunity vs. Passive Immunity
References
- Children’s Hospital of Philadelphia (CHOP). (n.d.). Types of immunity. Retrieved from https://www.chop.edu/centers-programs/vaccine-education-center/human-immune-system/types-immunity
- Kuby, J. (2013). Kuby immunology (7th ed.). W. H. Freeman.
- LibreTexts. (n.d.). Active and passive humoral immunity. Retrieved from https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Book%3A_Anatomy_and_Physiology_(Boundless)/20%3A_Immune_System/20.7%3A_Cell-Mediated_Immune_Response/20.7C%3A_Active_and_Passive_Humoral_Immunity
- Parija, S. C. (2016). Microbiology and immunology (2nd ed.). Elsevier.
- ThoughtCo. (n.d.). Active immunity and passive immunity. Retrieved from https://www.thoughtco.com/active-immunity-and-passive-immunity-4134137
- Wikipedia. (n.d.). Immunity (medical). Retrieved from https://en.wikipedia.org/wiki/Immunity_(medical)
- Technology Networks. (2020). Active vs. passive immunity: Differences and definition. Retrieved from https://www.technologynetworks.com/immunology/articles/active-vs-passive-immunity-differences-and-definition-335112
- Health.com. (n.d.). Active vs. passive immunity. Retrieved from https://www.health.com/condition/infectious-diseases/active-vs-passive-immunity
- BYJU’S. (n.d.). Difference between active and passive immunity. Retrieved from https://byjus.com/biology/difference-between-active-and-passive-immunity/
- Biology Online. (n.d.). Local immunity. Retrieved from https://www.biologyonline.com/dictionary/local-immunity
