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Topic 1 : Basic Immunology

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Xinyi Yap

on 31 July 2014

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Transcript of Topic 1 : Basic Immunology

Topic 1 : Basic Immunology
Immunity
DFN: State of having sufficient biological defenses to avoid infection, disease or other unwanted biological invasion
Define Immunology.
Study of defence mechanisms in the body against foreign environmental agents
1. Microorganisms
2. Products
3. Food
4. Chemicals
5. Drugs
6. Pollen
7. Animal Hair & Dander (skin)
4 major organs of Immune System
1. Thymus
1. Bilobed gland located on sternum
2. Stop growing after age 1, decreases in size at age 60
3. Where T-lymphocytes mature (produced in bone marrow)
2. Spleen
Filter blood (breakdown/destroy old RBC)
Antigen presentation (remove foreign materials)
Blood reservoir
size of clenched fist
located in left side of abdominal cavity
Lymphatic tissue surrounding arteries
(immunity)
Contains macrophages & RBC that connect to veins
(filters blood)
3. Bone Marrow
Generate all blood cells by Haemotopoietic stem cells
Myeloid stem cell
Lymphoid stem cell
1. RBC (anucleated)
2. Monocyte
3. Neutrophil WBC
4. Eosinophil
5. Basophil Granulocyte
6. Platelet (PMN - Poly-Mor-Pho-Nuclear cells)
1. T-lymphocyte
2. B-lymphocyte
3. NK Cell
4. Lymph Nodes
1. Rounded structure that vary in size
2. Located near lymphatic vessels
3. Can be felt easily in the groin, armpit and neck areas
Functions
1. Filter lymph fluid
2. Activate immune system via antigen presentation, where the foreign substances are detected
3. Removes microbes by macrophages
Eosinophil
Basophil
Neutrophil
Lymphocyte
Monocyte
- Unstained granules in cytoplasm (neutral, cannot pick up stain)
- Multi-lobed nucleus (normal: 3-4, abnormal > 5)
Function: Engulf & destroy foreign particles intracellularly (phagocytosis)
- Granules in cyto. stained
red by acidic stain (Eosin)
- Bilobed nucleus
- Kill parasitic worms
- Involved in allergic reactions
- Granules in cyto. stained purple
by basic stain (Haemotoxylin)
- Granules contain histamine which causes allergy
- Obscure nucleus
- Large cytoplasm
- Large C-shaped nucleus
- Becomes macrophage in tissues
- thin, scanty cytoplasm
- Nucleus similar in size to RBC
shape
Macrophage
*** 1. APC = Antigen-presenting cell
2. Active monocytes in tisues
3. Function: Pick up, ingest foreign materials & present antigens to other immune cells
4. Impt 1st step in the initiation of immune response
T suppressor cell (Ts)
T memory cell
T helper cell (T cell)
- secrete cytokines/interleukins to recruit other immune cells (Tc, Ts, B) to fight off infection

- mainly recognises MHC Class II molecules (APC)

* MHC Class I = all body cells
H
Major Histocompatibility Complex
Functionally & Phenotypically different
CD 4+
CD 8+
T cytotoxic cell (T cell)
C
Subclass 1 (cellular immunity)
Subclass 2
(recruit & activate)
1. Directly kill certain tumor and viral-infected cells (sometimes even parasites)
2. Induction of A-pop-to-sis
3. Releases perforins & granzymes

4. Recognise MHC Class I molecules
= Programmed cell death w/o any cell rxn due to destruction of cell's DNA
Forms a large pore on plasma membrane,
which causes osmotic destruction of cell.
Water rush in and cell burst (lysis).
Activates cas-pa-ses = enzymes involved in apoptosis
B cells
- Differentiate into plasma cells & secrete antibodies
1. aka. Immunoglobulins
2. specialised proteins
3. specifically recognise and bind to one particular antigen binding site (epitope on a antigen).

4. Antibodies production and ability to bind to foreign antigen is CRITICAL
5. Reason: it signals other cells to engulf, kill or remove a foreign antigen
Clonal Selection
After departure from bone marrow,
B cell activation + differentiation occurs on the periphery (outer layer) in the presence of antigen.
When a naive B cell encounters the antigen which matches its membrane bound antibody,
2nd exposure to antigen...
it proliferates (divides rapidly) and its progeny (offspring) differentiate into memory B cells + plasma cells
1. Express high affinity surface immunoglobins (antibody) which enable them to be activated by lower levels of antigen than naive B cells

2. Maintain immunological memory
3. Long-lived protection (vaccinations: give different bacterial antigens)
1. x produce membrane antibody, but SECRETE large amounts of antibody
2. Secreted antibodies = major effector molecule of humoral immunity
3. Short-lived & rarely found in circulation
#antibodies secreted = exponential (approx 10x)
Booster (antibodies dies overtime)
Natural Killer (NK) Cells
Kills cells naturally without
1. MHC presentation
2. Prior conference
3. Prior recognition & activation in immune system (Tc, B cell)

Neither T nor B lymphocyte
Similar to killer T cell subset (CD8+ Tc cells)
Function
Destroy infected cells & abnormal cancerous cells extracellularly
Viral infected targets/ tumours are killed off more effectively,
if NK cells were activated by CD4+ T cells secretions
Innate VS Adaptive
Present since birth
No immunological memory
Not antigenic specific

Involves Neutrophils & Macrophages

E.g.
Skin, cilia in respiratory tract, mucus secretion (Anatomical)
Fever, low pH in stomach, normal flora in large intestines (Physiological)
Endocytosis and phagocytosis
(Chemical - Enzymatic)
Acquired through exposure to foreign antigens
Develop immunological memory with T/B memory cells
Antigenic specific responses

Involves T and B cells

E.g. Hepatitis B
Vaccination
Infection
To activate adaptive immunity, the macrophages are important in presenting antigens with MHC Class II molecules to T-helper cells which secrete interleukins to recruit either Tc cells or B cells.
Humoral VS Cell-mediated
Involving antibodies

B cells differentiate into plasma cells (secrete antibodies) and memory B cells (for subsequent antigenic exposure)

E.g.
Bacterial infections
Involving cellular responses

T-helper cells – secrete interleukins to recruit T-cytotoxic or B cells
T-cytotoxic cells – secrete granzymes or perforins to kill target cells

E.g.
Tc cells in viral infected cells or tumor cells when MHC Class I molecules present foreign antigens to Tc cells.
Active VS Passive
Acquired through exposure of foreign antigens
Develop immunological memory with T/B memory cells

Involves T and B cells

E.g. Hepatitis B vaccinations & infections
Passive transfer of antibodies into non-immunized individuals
No immunological memory developed

Involves antibodies

E.g.
Serum injection
Breast-feeding
Season flu vaccine
Explain why the vaccine given last year can no longer provide protection to individuals for this year influenza infection.
Concept involved – antigen variations in influenza virus and antibodies developed can no longer recognise the viral antigens due to specific reactions between antigens and antibodies
HIV infection
Virus target host cell – T-helper cells (CD4+)
HIV viral infection in CD4+ cells stimulate cell-mediated immunity where CD8+ (Tc) cells kills CD4+ cells
Without CD4+ cells, other immune cells cannot be recruited during adaptive immunity
Leads to opportunistic infection occurring
Causing acquired immunodeficiency syndrome (AIDS)
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