Overview of the immune system Flashcards
Humoral immunity
Humoral immunity is also called antibody-mediated immunity. With assistance from helper T cells, B cells will differentiate into plasma B cells that can produce antibodies against a specific antigen. The humoral immune system deals with antigens from pathogens that are freely circulating, or outside the infected cells. Antibodies produced by the B cells will bind to antigens, neutralizing them, or causing lysis (dissolution or destruction of cells by a lysin) or phagocytosis.
Cellular immunity
Cellular immunity occurs inside infected cells and is mediated by T lymphocytes. The pathogen’s antigens are expressed on the cell surface or on an antigen-presenting cell. Helper T cells release cytokines that help activated T cells bind to the infected cells’ MHC-antigen complex and differentiate the T cell into a cytotoxic T cell. The infected cell then undergoes lysis.
Antigens
- Means antibody generator
- It is a molecule which is recognised by immune receptors
- Injection of animals with almost any non-self organic compound induces an immune response against this specific antigen
Tailored immune responses(Viruses, intracellular bacteria)
Identification and killing of infected cells by cytotoxic T cells
Tailored immune responses(Extracellular fungi, parasites, bacteria)
Detection of surface structures by antibodies and destruction by phagocytes
Tailored immune responses(Large parasites)
Deposition of toxic substances or killing by mast cells/eosinophils
Tailored immune responses(Bonus information)
- There is no response in immunopriveleged areas (e.g. CNS, placenta, eyes)
- Tolerance of commensal bacteria in the gut (microbiota)
Three levels of defence against invaders
- External defences
- Innate immune system “primitive”
- Adaptive immune system (highly specific)
Innate immune system “primitive”
- Non-specific
- Fast response (minutes)
- No memory
Adaptive immune system
- Highly specific
- Slow response (days)
- Memory
Immune dysregulation
- Hypersensitivity - Overreaction to benign antigens
- Autoimmunity - Attack against self-proteins or tissues
- Immunodeficiency - Failure to protect against foreign antigens
Autoimmunity
- Immune system must distinguish between ‘self’ and ‘non-self’ - Tolerance
- Self-reactive immune cells usually eliminated by the immune system
- Breakdown of tolerance –> autoimmunity
- Genetic and environmental factors
Immunodeficiency
- Component of innate/adaptive immune system absent or defective
- Inherited - primary immunodeficiency
- Severe combined immunodeficiency (SCID) - no functional adaptive immunity
- Damage by external agents - secondary immunodeficiency
- Acquired immune deficiency syndrome (AIDS) - infection with HIV, destruction of T helper cells
