Immune System Explained: Types, Disorders, and Allergic Reactions

Understanding Immunity: Types, Disorders, and Hypersensitivity

Types of Immunity

• Natural Passive Immunity

  This process involves the body receiving antibodies without producing its own. Antibodies are transferred through the placenta during embryonic development or via breastfeeding until the infant's immune system fully develops.

• Active Natural Immunity

  Antibodies are formed naturally when the body comes into contact with a pathogen. The individual develops immunity after exposure to the disease.

• Active Artificial Immunity

  The body produces its own antibodies through vaccination. Vaccines contain attenuated or killed pathogenic organisms that stimulate the immune system to create active immunity without causing the disease.

• Passive Artificial Immunity

  This is an artificial process where the body does not manufacture its own antibodies. Instead, pre-formed antibodies are administered, typically through serum. Serum is the fluid part of blood remaining after coagulation, without clotting factors. Sera from animals inoculated with pathogenic microorganisms contain specific antibodies, which are then injected into the recipient to provide immediate, temporary immunity.

Disorders of the Immune System

• Autoimmune Diseases

  Normally, the body's immune system can recognize its own cells and molecules. However, in autoimmune diseases, this recognition fails, triggering immune responses against the body's own tissues. Sometimes, molecules referred to as "sequestered antigens" are involved. During the immune system's development, it develops tolerance to self-molecules, but not necessarily to these sequestered antigens. When the immune system fails to recognize them as "self," it mounts an attack against these antigens as a defense mechanism.

  Examples include:

  • Hemolytic Anemia: The immune system attacks the body's own erythrocytes (red blood cells).
  • Thyroiditis: An autoimmune disease affecting the thyroid gland, where antibodies attack thyroglobulin.
  • Pernicious Anemia: The immune system attacks a protein essential for the intestinal absorption of iron.

Hypersensitivity Processes (Allergies)

Hypersensitivity refers to an exaggerated or severe reaction to an antigen, more intense than expected. These processes are commonly known as anaphylaxis or allergic reactions. There are two main types of hypersensitivity:

• Immediate Hypersensitivity

  In these reactions, the immune response to an antigen appears rapidly, typically within a few minutes (1-5 minutes).

• Delayed Hypersensitivity

  The reaction time for delayed hypersensitivity can range from a few hours to several days.

Mechanism of Immediate Hypersensitivity

This is a humoral, sensitive, and specific process. When an antigen (allergen) enters the body, the immune system creates specific IgE antibodies against it. These IgE antibodies bind to mast cells and basophils. Upon subsequent exposure to the same allergen, the allergen binds to the IgE antibodies on these cells, triggering the release of histamine and serotonin. These mediators then cause the symptoms of an allergic reaction, such as swelling, coughing, and redness.

Mechanism of Delayed Hypersensitivity

This is a cell-mediated process with a specific immune response, primarily mediated by T lymphocytes. Upon the entry of an antigen, T lymphocytes bind to it and release chemicals (cytokines) that attract macrophages and other immune cells to the site. Helper T cells are crucial in orchestrating this response. Examples include sensitivity to certain substances like latex or the reaction to a tuberculin skin test.