Immunity

• Use white blood cells with specific complementory antigen receptors to bind and detect antigens in the body.
• WBC recognise them as self or non-self 
• Only non-self are attacked with an immune response 
• Objective= remove all non-self and produce antibody immunity to them 

• Proteins that have specific 3D shape.
• Found on cell surface membranes of Eukaryotes and prokaryotes.
• Found in capsid of viruses.
• Act as recognition devices and trigger an immune response.
• Proteins on own healthy cells= self antigens
• Not from your own healthy cells= foreign non-self antigens. 

• Non-specific- barriers and phagocytes 
• Specific- humoral (B lymphocytes) and cell mediated (T lymphocytes)
• barriers-physical (skin), chemical (sweat) and mechanical (sneezing)               

• Have non-specific innate receptors for recognising foreign cells
• Ingest and destroy pathogen in phagocytosis.

Neutrophil 

• produced in bone marrow.
• move from blood vessels to infection
• form puss
• 60-70% of WBC population 

Macrophage

• begin as monocyte in blood
• can engluf damaged cells
• found where infection is more likely
• larger than neutrophils 

• Pathogen with foreign antigens on its surface are detected by phagocytes.
• Phagocyte engulfs pathogen and traps in in a vacuole.
• Phagosome fuses with lysosome to form a phagolysome and it releases hydrolytic enzymes over it.
• Partly digested remains of pathogen become antigens which phagocyte can present to the immune system.
• They are removed by exocytosis. 

• Involved in cell mediated immunity 
• Destroy abnormal and foreign cells
• Made in bone marrow and mature in thymus
• 3 types- T helper- activate phagocytes and B cells using cytokines

               - T cytotoxic- kill foreign cells using cytokines 

               - T memory- provide long term immunity 

• Phagocyte displays foreign pathogen's antigen on its surface
• T helper cells bind to antigen using specific complementory recpetors (clonal selection)
  
• This triggers activated T cells to divide by mitosis to produce clones (clonal expansion)
• T cell then differentiates into 1 of 3 types of T cell

• Mature in bone marrow and have their own uniquely shaped antibodies on its surface.
• Activated when in contact with complementory-shaped antigens and signals from Th cells.

Clonal selection

• B cell with specific and complementory antibody on CSM is selected.
• B cell takes in pathogen and breaks it down
• Th binds to antigen on B cell

Clonal expansion

• B cell differentiates into B memory cells and plasma cells
• Plasma cells release antibodies 
• These antibodies bind to the pathogen and fight infection

Plasma cells

• Quickly produce same antibody then die
• Specific antibody produced by plasma cell is also secreted in soluble form and circulates in blood and lymph

Memory cells

• Long-term immunity
• If same antigen is reintroduced they divide rapidly and develop into plasma and more memory cells. 
• Secondary response is quicker than primary because there is more antibodies produced

• Proteins used by lymphocytes in response to antigen
• Made of 4 polypeptide chains held by disulphide bonds
• Constant region allows antibody to bind to receptors of phagocytes
• Variable region only binds to antigen of specidic complementory shape to form an antigen-antibody complex
• Hinge region allows flexibility to bind with more than 1 pathogen 

• Antibodies produced from a single group of genetically identical B cells so identical in structure
• Used to target specific cell types as antigen binding sites have a unique structure that only 1 antigen will fit into it
• Ethical issues= produced in animals, dealths associated and testing safety issues
• Can be used for cancer treatments, pregnancy tests and medical diagnosis
  

• Detect human chronic gonadotropin (HCG)
• Monoclonal antibodies with  blue beads attached binf to HCG in urine
• Antigen- antibody complex is trapped by 2nd set of monoclonal antibodies

• ELISA tests- enzyme linked immunoabsorbent assay

Direct

• tests for antigens for a specific pathogen
• Indicates if someone has active disease/taking a drug
• Antigen in serum sample fixed in well
• MA binds to antigen
• Substrate added to well reacts with enzyme

Indirect

• Tests if making antibodies for a specific pathogen 
• Indicates if someone has had/ is currently fighting a disease
• Antigen fixed in well
• Primary antibody from serum binds to antigen 
• Secondary antibody binds to primary
• Substrate added to well reacts with enzyme 

Active

• Make your own antibodies
• Develops slowly
• Long-term

Passive

• Given antibodies
• Immediate
• Short-term

Natural Active- Infection:contact with pathogen- personal antibodies made

Artificial Active- Vaccination with pathogen- personal antibodies made

Natural Passive- Antibodies given- breast milk, across placenta

Artificial Passive- Antibodies given- injection of blood plasma containing antibodies