Innate vs. Acquired Immunity (Definition, Types, Examples)


The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, distinguishing them from the organism`s own healthy tissue. The immune system also helps to maintain homeostasis and regulate inflammation.

The immune system can be divided into two major branches: innate immunity and acquired (adaptive) immunity. Innate immunity is the non-specific arm of the immune system that an individual is born with. It acts as a barrier against foreign invading materials and provides immediate defense against infections. Acquired immunity is the specific arm of the immune system that is developed during an individual`s lifetime. It involves the recognition of specific antigens and the generation of immunological memory.

The immune system consists of various types of cells and molecules that are distributed throughout the body. Some of these cells and molecules are specialized for innate immunity, while others are specialized for acquired immunity. Some of them can perform both innate and acquired functions. The main components of the immune system include:

  • Physiological and anatomical barriers: These include the skin, mucous membranes, gastric acidity, enzymes, antimicrobial peptides, and other factors that prevent or limit the entry of pathogens into the body.
  • Phagocytes: These are cells that can engulf and destroy foreign particles or microorganisms by a process called phagocytosis. Examples of phagocytes include macrophages, neutrophils, dendritic cells, and monocytes.
  • Inflammatory reactions: These are responses that occur when host tissue is damaged or infected by pathogens. They involve the release of various mediators, such as histamine, cytokines, defensins, and kinins, that cause increased blood flow, swelling, redness, pain, and heat at the site of injury or infection. Inflammation helps to recruit more immune cells and molecules to the affected area and facilitates healing.
  • Complement system: This is a group of proteins that circulate in the blood and can be activated by pathogens or antibodies. The complement system enhances the ability of phagocytes to clear infections, promotes inflammation, and directly kills some pathogens by forming pores in their membranes.
  • Natural killer (NK) cells: These are lymphocytes that can recognize and kill cells that are infected by viruses or transformed by cancer. NK cells do not need prior exposure to antigens to function. They use receptors that can detect abnormal or missing self-molecules on the surface of target cells.
  • Antibodies: These are proteins produced by B lymphocytes that can bind to specific antigens with high affinity and specificity. Antibodies can neutralize pathogens or toxins, opsonize them for phagocytosis, activate complement, or recruit other immune cells to eliminate them.
  • T lymphocytes: These are lymphocytes that can recognize antigens presented by specialized cells called antigen-presenting cells (APCs). T lymphocytes can be divided into two main types: helper T cells and cytotoxic T cells. Helper T cells secrete cytokines that regulate the activity of other immune cells. Cytotoxic T cells can kill infected or abnormal cells by releasing perforin and granzymes.
  • Regulatory T cells: These are a subset of T lymphocytes that can suppress excessive or unwanted immune responses. Regulatory T cells help to prevent autoimmune diseases, allergies, chronic inflammation, and transplant rejection.

The immune system is constantly surveilling the body for signs of infection or damage. When it encounters a foreign material or a pathogen, it initiates an immune response that involves both innate and acquired components. The innate immune response is rapid and non-specific, while the acquired immune response is slower but more specific and effective. The acquired immune response also generates immunological memory, which allows for a faster and stronger response upon re-exposure to the same antigen.

The immune system is essential for maintaining health and preventing diseases. However, sometimes it can malfunction or be overwhelmed by pathogens. This can result in immunodeficiency disorders, autoimmune diseases, allergic reactions, chronic inflammation, or cancer. Therefore, it is important to understand how the immune system works and how it can be modulated by various factors, such as vaccines, drugs, nutrition, stress, and lifestyle.