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Flashcards in Innate and Adaptive Immunity Deck (27)
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What are the roles of the immune system?

Immunity to infection

Inflammatory processes

Removal of senescent cells

Defence against neoplasia



Define antigen

A substance capable of generating a specific immune response 


Which antigens are mainly targeted by the innate immune system?

Antigens with pathogen associated molecular patterns (PAMPs)


Define innate immune system

Immediate response to an antigen which recognises certain but not all threats. Does not involve clonal selection, antigen presentation or immunological memory. 

Primary defence


Define adaptive immune system 

Secondary line of defence.

Delayed immune response that recognises all threats. Involves immunological memory, antigen presentation and clonal selection. 


What are the different types of barrier immunity?

Give examples 

  • Physical barriers: 
    • Skin
    • Respiratory cilia
    • Mucus
    • Commensal organisms
  • Biochemical barriers:
    • Sebaceous skin secretions
    • Lysozyme in tears
    • Spermine in sperm
    • Gastric acidity


How do most infectious agents enter the body?


  • Nasopharynx
  • Respiratory tract
  • GI tract
  • Genito-urinary tract


List the components of the innate cell-mediated immune system

2 main cell types:

  • Phagocytes:
    • Neutrophils: polymorphonuclear phagocytes (mostly innate immunity)
    • Antigen presenting cells- monocytes and macrophages 
  • Natural killer cells


Describe the process of phagocytosis

  1. Chemotaxis and adherence of microbe to phagocyte
  2. Ingestion of microbe by phagocyte
  3. Formation of phagosome 
  4. Fusion of phasosome with lysosome: phagolysosome
  5. Digestion of microbe by enzymes from lysosome. 
  6. Formation of residual body containing indigestible material
  7. Discharge of waste materials by exocytosis. 


Describe the role of natural killer cells

Perform under direct and indriect antibody-dependent cell cytotoxicity (process remains innate).

  1. Detect loss of MHC class I molecules in infected or malignant cells (normally present on healthy cells) and become activated.
  2. Inserts pore-forming molecules into target cell and pumps in cytotoxic chemicals resulting in cell lysis. 


What are the types of barrier immunity?

Give examples

Physical barriers: skin, respiratory cilia, commensal organisms, mucus.

Biochemical barriers: lysozyme in tears, sebaceous skin secretions, spermine in sperm, gastric acidity. 


List the components of innate humoral immunity

Acute phase proteins: 

  • CRP
  • Pro-calcitonin
  • Alk phos
  • Ferritin



Describe the acute phase proteins of innate humoral immunity

  • Produced in response to PAMPs
  • Immediate/ non-specific cytotoxicity
    • e.g. CRP, pro-calcitonin, alkaline phosphatase, ferritin.
    • CRP binds to surface molecules of bacteria and fungi (not viruses), has some inhibitory effects and promotes complement binding. 
      • Therefore raised in bacterial and fungal infections but not in viral.


Describe the classic and alternative pathways of complement

What is needed to inhibit these pathways?

  • Classic: anti-body dependent cell lysis.
  • Alternative:
    • ​C3 cleaved in presence of microbe
    • C3a → chemotaxis and local anaphylaxis inflammation
    • C3b → opsonisate of microve, cleavage of C5
    • C5a → chemotaxis and local anaphylaxis (inflammation)
    • C5b → attaches to microbe and activates C6,7,8 & 9.
    • C5b, 6, 7, 8 & 9 = membrane attack complex → cell lysis. 

C1 needed to inhibit these pathways.



Which immune cell tends to predominate in acute infections?

What part of the immune system are they part of?


Innate immunity mostly.


Which immune cell tends to predominate in parasitic and allergic infections?



Which immune cells would predominate in inflammatory and hypersensitivity reactions?

Basophils and mast cells 


List the components of adaptive cell-mediated immunity. How do these cells respond to an antigen?


Cytotoxic T cells (TC)

  • Cells present antigen to TC cells using MHC class I molecule. If the antigen is recognised as foreign, TC cells replicate and differentiate. 
    • Memory TC (TCM) cells are activated and maintain immunological memory of that antigen. 
  • Each TC lymphocyte only recognises one antigen. When that antigen is detected, clonal selection and expansion occur, ensuring a specific response and memory. 


Describe the process of clonal selection

Each T and B lymphocyte are responsive to only one antigen. When that antigen is detected, the T or B lymphocyte with the 'best fit' for that specific antigen is selected and replicates.

As it replicates, the antibodies it produces evolve slightly due to genetic recombination.  The cell with the most appropriate antibody for that antigen then replicates further ensuring a specific response. (expansion). 


List the components of the adaptive humoral immunity

Describe the role of these components.

B lymphocytes & TCells 

  • Cells present particles of phagocytosed microbe to TH cells via MHC class II molecules.
  • TH cells activate B cells which replicate and differentiate:
    • BP (plasma) cells produce antibodies for that specific antigen
    • BM (memory) cells maintain immunological memory of that antigen
    • Genetic recombination, clonal selection and expansion ensure specific response and memory. 



What are the stimulating factors involved in control of the immune system?

  • Presence of an antigen
  • TH cells
  • Cytokines 


What are the inhibiting factors involved in control of the immune system?

  • Removal of antigen
  • TS cells
  • Cytokine breakdown


What are the 2 processes involved in immunological tolerance?

Negative selection (deletion) of immune cells that recognise self-antigens.

Development of regulatory T cells that regulate cells that recognise self-antigens. 


Where are MHC class I and II molecules found?

What do they present?

  • MHC class I:
    • On all cells except erythrocytes
    • Presents host, viral, neoplastic cells to Tc lymphocytes
  • MHC class II:
    • On antigen presenting cells only
    • Present ingested microbial agents to TH lymphocytes which interact with B lymphocytes to produce antibodies. 


Describe T-cell cytotoxicity

Replication of TC cells triggered upon binding of MHC class I to T cell receptor if presented antigen is foreign. 


Describe the role of interleukins and TNF in the control of the immune system

  • Interleukins:
    • Produced by the MPS and TH cells
    • Up-regulate the immune system: increase proliferation, differentiation, activation and chemotaxis.
    • Autocrine and paracrine
  • TNF (tumour necrosis factor):
    • Produced by MPS cells
    • Upregulates immune system, leads to fever, inflammation, enhanced immunity, septic shock, cachexia and anorexia.



Describe the role of interferons in the control of the immune system

  • Produced by virus-infected cells and TH cells
  • Activate NK cells and TC cells leading to increased cytotoxicity, make other cells virus-reistant
  • Also activate macrophages and up-regulate antigen presentation.