The purpose of the immune system is to maintain normal health, and hence an abnormal immune response may cause disease
- The immune system may over-react (hypersensitivity), fail to distinguish ‘self’ and ‘non-self’ (autoimmune conditions) or cease working entirely (immunodeficiency)
Hypersensitivity Disorders
Hypersensitivity refers to an excessively disproportionate immune response to a substance that is not inherently harmful (allergen)
- Such reactions require a pre-sensitised immune state (prior exposure), with an excessive reaction occurring upon re-exposure
- Allergic reactions are examples of localised hypersensitivity conditions, while anaphylaxis is a more severe, systemic example
Autoimmune Disorders
Autoimmunity occurs when the immune system fails to recognise body cells as ‘self’ and begins targeting its own cells and tissues
- Some pathogens try to evade immune detection by producing antigens that closely resemble host markers (antigenic mimicry)
- Detection of these pathogens will lead to the production of antibodies that will recognise and target markers on body cells
- Examples of autoimmune diseases include diabetes (type I), rheumatoid arthritis and multiple sclerosis
Immunodeficiency Disorders
Immunodeficiency is a state in which the immune system’s capacity to fight infection is compromised or absent entirely
- These disorders may be inherited (e.g. SCIDs), pathogenic in origin (e.g. AIDS) or caused by drug treatments
- Cytotoxic drugs which cause immunosuppression are commonly used during transplant operations to avoid graft rejection
Immune System Disorders Analogy
