⋆˚࿔✮⋆˙Making Science Fun! (1st Entry)

Topic: Immunity

⋆｡˚⭒°✮˙⋆Important Definitions⋆˙✮°⭒˚｡⋆

• White Blood Cells - Cells found in our blood that recognise and destroy pathogens 
• Antigens - Macromolecules on the cell surface membrane that stimulates an immune response.
• Antibody - Y-shaped protein molecule which is complementary to a specific antigen and binds to it, to neutralise or destroy it.
• Pathogens - A disease-causing organism.
• Lymphocytes - WBCs that recognise specific pathogens and directly or indirectly kill them (specific immune response).
• Phagocytes - Neutrophils and Monocytes, which engulf and digest pathogens (non-specific immune response).
• Neutrophils - WBCs with lobed nucleus found mainly in the blood involved in phagocytosis.
• Monocytes - WBCs with kidney shaped nucleus found mainly in blood involved in phagocytosis.
• Macrophages - A type of phagocyte that develops from monocytes after they leave the blood, found in lymph, tissue fluid, and lungs. 

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The Non-Specific Immune Response

°✮⋆ Phagocytosis ⋆˙✮°

Phagocytosis is a type of endocytosis carried out by Phagocytes (Neutrophils and Monocytes) which are produced in the bone marrow. They have a cytoskeleton and many mitochondria for the production of ATP.  Here are the steps:

1. A pathogen is recognised, and the macrophage forms a pseudopodia* around it. 
2. The ends of the pseudopodia meet and the cell surface membrane fuses together to form a phagosome which is vacuole enclosing the pathogen
3. The phagosome moves deeper into the cytoplasm of the macrophage and fuses with a lysosome, which digest the pathogen into smaller fragments.

*Pseudopodia is the membrane of the phagocyte that extends and surrounds the pathogen.

 The Specific Immune Response

°✮⋆ Humoral Immunity ⋆˙✮°

1. B-cells are produced and mature in the Bone marrow, and specific B-cell antibodies build up on their surface.
2. B-cells respond to foreign antigen by differentiating into plasma cells. Why? Because Plasma cells have many ribosome on rough ER and lots of mitochondria to produce ATP, for the production of antibodies (proteins).
3. Antibodies are released into the blood plasma and go to site of infection.
4. Antibodies bind to Antigen on the surface of foreign pathogen, to neutralise them and mark them for destruction.

°✮⋆ Cell-Mediated Immunity ⋆˙✮°

1. T-cells are produced in the bone marrow but mature in the Thymus gland, and protein receptors build up on their surface membrane 
2. Like B-Cells, T-cells respond to foreign antigen, but they do it by differentiating into two different types of T-cells; T-helper cells and T-killer cells.
3. T-helper cells produce cytokines* for phagocytosis, stimulate T-killer cell and stimulate B-cells to differentiate into plasma cells.
4. T-killer cells (aka Cytotoxic T-cells) attack infected body cells and pathogens directly. They are specific for the presented antigens, Why? So they kill only body cells that express these antigens, ensuring that only infected cells are destroyed and not healthy cells. 
5. T-killer cell and antigen presenting cell face each other, cell membranes touching, and T-killer cell secretes hydrogen peroxide or perforin* by exocytosis. These form holes in target cell's surface membrane. 

*Cytokines are chemicals that circulate in the blood and stimulate phagocytes to undertake phagocytosis

*Perforin is a protein that creates a channel through a membrane, allowing cytolytic proteins to enter a cell and trigger it to self-destruct

white blood cells under the microscope :)