This video is about Antigen presenting cells:
Content:
0:00 Introduction
0:10 Function of Antigen-Presenting Cells (APCs)
3:01 Types of APC
4:29 B-Lymphocyte Development
9:33 B-Lymphocyte Function
15:43 Macrophage/Dendritic Cell Development
17:11 Macrophage Function
22:40 Dendritic Cell Function
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All information in my immunology videos are from:
- Book: Immunology, Eighth Edition by David Male, Jonathan Brostoff, David Roth and Ivan Roitt
- Additional research in PubMed
- University lecture materials
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What are antigen presenting cells (APC)?
- Phagocyte microorganisms and present them on MHC I or MHC II
- They express B7 (Co-stimulator for T-cells)
- Presents MHC II to Naive T-Helper Cells (CD4+ cells).
3 activation signals are required to activate naive T-helper cells:
1st activation signal: MHCII-TCR(CD4 and CD3)
2nd activation signal: B7 - CD28
3rd activation signal: Interleukins
- MHC I activate T-cytotoxic cells (CD8+ cells)
Professional Antigen Presenting Cells:
- B-Lymphocytes
- Macrophages
- Dendritic Cells
Inactive/unprofessional antigen presenting cells:
- Langerhans Cells
B-Lymphocytes:
- Normal: Antibodies produces against specific antigens
- B-cells produce surface antibodies randomly during development. Apoptosis happen if they are not exposed to antigens whithin a certain amount of time (Anergy)
B-Lymphocyte Developement:
- In Spongy Bone:
- Start as Pluripotent Hematopoietic Stem Cell
- Pro B-Cell
- Pre B-cell (Recombination of Heavy chain for IgM gene VDJ gene)
- Immature B-cell (Recombination of light chain gene VJ gene) IgM development complete
- Mature B-cell have IgM and IgD antibodies on surface
- Then they're controlled whether they self react or not. If non self reactive - Travel to secondary lymphoid organs (Lymph node, spleen, payers patches)
B-Lymphocyte steps of activation:
- B cell receptor (BCR) consist of IgD/IgM and signal chains (Iga and Igb)
- B-cells are located in outer cortex of lymph node.
1. BCR react with antigen
2. BCR mediated endocytosis
3. Present it on MHC II to Th2 or Th0
4. Th2 binds to activated B-cell through (CD40L-CD40) and (TCR-MHCII)
5. Cytokines released to help B-cell differentiate (IL-4, IL-5, IL-10, IL-6, IL-2 and IFN-g)
6. B-cell become Memory B cell and Plasma Cells (specific type of plasma cell)
- When T-cells help B-cells differentiate (T-cell dependent B-cell differentiation) - They become IgA, IgE or IgG
- T-independent B-cell differentiation: Quick process which produce IgM when a polysaccharide binds to BCR and activate B-cells. No memory B-cells are produces.
Macrophages Developement:
1. Pluripotent hematopoietic Stem Cell
2. Mono Stem Cell
3. Pro-monoblast
4. Monoblast
5. Pro-monocyte
6. Monocyte in blood
7. Monocyte become Free macrophage in tissue, fixed macrophages or dendrittic cell
Functions of Macrophage:
- MHC 1/2
- Fc IgG (direct opsonization)
- Fc IgE
- C3b receptor for C3b of complement
- CD14 for Lipopolysaccharide (LPS)
- B7
Active Macrophage can release:
- Interleukin 12 (IL12) - differentiate Th0 to Th1 and activate Natural Killer cells
- Interleukin 8 (IL8) - Chemotaxis
- Interleukin 1, Interleukin 6 and Tumor necrotic factor alpha work as endogenic pyrogens
- IL1, IL6 and TNFa goes to hypothalamus
- Hypothalamus release Prostaglandins E2
- IL6 can travel to liver and cause release of Acute phase proteins
Dendritic Cells:
- Come from monocytes in the blood
- Can migrate easily
Surface of Dendritic cells:
- MHC1 and MHC 2
- B7
- Adhesion molecules that promote T-ly attachment.
Langerhans cells:
- Also called immature dendritic cell
- Once they phagocyte, they travel to lymph node and start to express B7
