The Immune System

Pathogen

An enemy cell that causes damage/illness to the human body. Takes nutrients and produce toxins.

Antibodies

Clump (agglutinate) pathogens together by attaching them to their complementary antigens. This makes it easier for WBCs to phagocytosise; makes it more obvious to phagocytes (acts as a marker). The pathogens are unable to move.

They prevent pathogens from functioning / reproducing

1 antibody = 2 binding sites

Antibodies can attach to toxins to neutralise the toxin

Physical Barriers

Skin

Prevents invasion by microorganisms

• Normal flora compete for microenvironments more effectively than pathogens

  • Produce nutrients

  • Resistance to colonisation by pathogens

Mucous Membrane

• Found in lining of mouth, nose, vagina, eyelids

• Coated with secretions that fight microorganisms

Tears

• Lysozyme

  • Attach bacteria

  • Protect eyes from infection

Airways

• Filter out particles in the air that are inhaled

• Coated in mucus

  • Microbes in the air because stuck to the mucus

• Cilia

  • Sweeps mucus up the airways; away from lungs

Digestive Tract

• Stomach acid

• Pancreatic enzymes

• Bile

• Intestinal secretions

They all either kill bacteria or stop them from multiplying

Urinary Tract

When bladder empties, it flushes out the bacteria that reach it.

Vagina

Acidic: Prevents harmful bacteria from growing

Ear Wax

Trap and preventing dust from entering ear from entering and damage the ear

Sweat

Contain antimicrobial peptides; help immune system ward off bacteria or fungi

WBC - Phagocytes

Macrophage

Moves around to remove dead cells and foreign bodies

Produce inflammatory molecules (cytokines) that activate other cells

Displays antigen and presents it to B & T Lymphocytes so that they can attack the particular pathogen

Neutrophils

Most abundant type of WBC.

Attracted to site of infection by cytokines and other microbial chemicals released by macrophages

• Chemotaxis

  • Move towards chemical products from bacteria

Phagocytosis

1. Phagocytes attach themselves to the antigens of the bacteria

2. The phagocytes engulf the bacteria to form a phagosome

3. Lysosome move towards the phagosome and fuse with it

4. Hydrolytic enzymes released by lysosome breakdown bacteria

5. Soluble products from breakdown of pathogen are dissolved into the cytoplasm of the phagocyte

6. Antigens from the pathogen are displayed on phagocyte cell membrane

WBC - Lymphocytes

Each lymphocyte is specific and complementary against a particular antigen.

They have receptors on the outside of the cell surface membrane

Activated when they encounter their complementary antigen either on the pathogen itself or just floating about in the body.

Activation causes “clonal expansion”

• Activated lymphocyte makes copies of itself through mitosis

T Cells

Helper T Cells

Capable of helping B cells divide; release cytokines to stimulate B cells to develop

Killer T Cells

Capable of killing infected cells by releasing cytotoxins (perforin)

Regulatory T Cells

Regulate immune cells (stops them from causing damage to your own cells)

Memory T Cells

Helps the response become faster when the same antigen is detected in the body again. When the same antigen is detected again, these cells trigger a quicker and stronger response by rapidly differentiating into active T cells, enabling the immune system to combat the pathogen more efficiently than during the first exposure.

B Cells

Plasma Cells

Antibody secreting cell

Memory B Cells

Readily stimulated to form plasma cells if re-exposed to the antigen at a later date

Immunity

Having correct antibodies available quickly to kill a pathogen BEFORE getting symptoms

Active Immunity

Your B Cells make the antibodies

Natural Immunity

Lymphocytes naturally make their own antibodies when pathogens invade the body

Artificial Immunity

Using vaccinations with antigens / weak form of a pathogen to stimulate antibody production

Passive Immunity

You are given the antibodies

Natural

Antibodies pass through breast milk/through placenta from mother to baby

Artificial

Antitoxins / Antibodies are injected into individuals

Active Immunity Key Facts

• Exposure to antigen is needed

• Takes time for protection to be developed

• Long-Term protection

• Memory Cells are produced

Passive Immunity Key Facts

• Exposure to antigen is not needed

• Protection is immediate

• Short-Term protection

• Memory Cells are not produced

Monoclonal Antibodies

1. Immunization: Mice (or other suitable animals) are immunized with an antigen that you want to produce antibodies against. This stimulates their immune system to produce specific B cells that respond to the antigen.

2. Cell Fusion: Spleen cells from the immunized mouse (which produce antibodies) are fused with myeloma cells (cancerous cells that can divide indefinitely) using a fusion agent such as polyethylene glycol (PEG). This results in hybridoma cells that have qualities of both cell types.

3. Cloning: The positive hybridomas that produce the desired antibodies are cloned to create many identical cells. This ensures a uniform antibody production.

4. Harvesting and Purification: The antibodies produced by the cloned hybridoma cells are harvested from the culture medium and purified to remove other proteins and components, resulting in a concentrated solution of monoclonal antibodies.

Can be used for a

• Pregnancy Test

• Show the location of cancer cells

• Identify blood clots

• Cancer Treatment

Negatives of Monoclonal Antibodies

Expensive ; Have side-effects ; long time to make them

ELISA TEST

1. Sample Addition: The biological sample (e.g., blood serum) is added to the wells. If the target antibodies are present in the sample, they will bind to the coated antigen to form immune complexes.

2. Detection Antibody Addition: A secondary antibody that is specific to the target antibodies and is usually conjugated with an enzyme or a marker is added to the wells. This detection antibody will bind to the target antibodies, forming a sandwich complex.

3. Substrate Addition and Measurement: A substrate that reacts with the enzyme linked to the detection antibody is added. A color change or fluorescence occurs, which is then measured. The intensity of the signal is proportional to the amount of target antibodies in the sample.