Immunology and Disease

Immunology and Disease

Introduction to Immunology

  • Immunology is the study of the body’s defence mechanisms against pathogens.
  • The immune system can be classified into two main types: innate immunity and adaptive immunity.
  • Innate immunity consists of responses that the body mounts automatically to any type of pathogen. This includes physical barriers such as skin and mucous membranes, acids in the stomach, and certain types of white blood cells like phagocytes.
  • Adaptive immunity, on the other hand, involves specific responses to particular pathogens and develops over time with exposure to various pathogens.

Cells of the Immune System

  • The immune system is composed of a variety of cells, the most important of these being white blood cells or leukocytes.
  • These include phagocytes such as neutrophils and macrophages, and lymphocytes including B cells and T cells.

Antigens and Antibodies

  • An antigen is any substance that can stimulate an immune response. Pathogens carry antigens on their surfaces, which the immune system recognises as foreign.
  • Antibodies are proteins produced by B lymphocytes in response to antigens. Each antibody molecule has a specific shape that matches a specific antigen, allowing it to bind to and neutralise the target.

Immune Response

  • The immune response is generally divided into two stages: the primary and secondary response.
  • In the primary response, when an antigen first enters the body, the immune system produces antibodies to combat it. This response is slowed because the body has to ‘learn’ to recognise the antigen and produce the appropriate antibodies.
  • If the same antigen enters the body again, the secondary response is faster and stronger as the immune system ‘remembers’ the antigen and quickly produces the correct antibodies.


  • Vaccines contain weakened or inactive parts of pathogenic organisms that trigger an immune response without causing disease.
  • They stimulate the production of memory cells, speeding up and enhancing the secondary response to future encounters with the same pathogen.

Non-Specific Defence Mechanisms

  • These include physical barriers like skin and mucus, chemical barriers like stomach acid and tears, and cellular defences like phagocytes.
  • Inflammation and fever are also non-specific defences, where the body raises its temperature to create an unfavourable environment for bacteria and viruses.

Allergies and Autoimmune Disorders

  • Allergies are exaggerated immune reactions to substances that are generally harmless, such as pollen or dust mites.
  • Autoimmune disorders involve the immune system mistakenly attacking the body’s own cells, treating them as if they were foreign invaders.

Infections and Diseases

  • Pathogens, including bacteria, viruses, fungi, and parasites, can cause infections leading to diseases.
  • Infectious diseases can spread in various ways, including direct contact, droplets in the air, food and water, vectors like mosquitoes, and animals.

Antibiotic Resistance

  • Overuse and misuse of antibiotics have led to the rise of antibiotic-resistant bacteria.
  • These bacteria can survive and multiply in the presence of antibiotics, making infections more difficult to treat.

Health Impact and Community Immunity

  • An individual’s health and their immune response can be influenced by several factors including diet, stress, and aging.
  • Community immunity or herd immunity is a form of indirect protection from infectious diseases that can occur when a large percentage of a population has become immune to an infection, providing some protection for individuals who are not immune.