4.1.5(Secondary non-specific immune responses)

State when secondary defences are activated

• They are activated when pathogens have entered the body

Describe how out body detects its own cells

• On our cells we have antigens

• These antigens are specific to each organism

Describe and explain the role of antigens in fighting pathogens

• Antibodies are on the outside of the pathogen or cell

• When pathogens invade the body, the immune system can use the antigens on the surface of it to identify it as a foriegn object.

• This then triggers an immune response and WBCs start trying to fight the pathogens

Describe and explain the role and function of opsonins

• Opsonins are protein molecules that are a type of anti boy that attach to the antigens on the surface of the pathogen

• Some opsonins are not very specific so that they can attach to a variety of pathogenic cells

• The role of opsonin is to enhance the ability of phagocytic cells to bind and engulf the pathoge

State what is the first line of secondary defence and describe their role

• Phagocytes

• They are specialised cells in the blood and tissue fluid and they ingest and digest pathogens

Give 3 example of phagocytes

• Neutrophils

• Monocytes

• Macrophages

State the most common type of phagocytes

• Neutrophils

• They make up 50-75% of white blood cells

Describe and explain how neutrophils travel in the body

• They travel in the blood and often squeeze out of the blood into tissue

  • This is made possible by their multi-lobed nucleus

• They move towards the wound in response to signals from cytokines

  • These are messenger proteins released at the site of the wound

• They are the first to arrive to the site of infection and generally arrive within the first hour of the infection being detected

Describe what happens to neutrophiles during their life and after

• Neutrophils are short-lived, but are released in large numbers as a result of infection

• They will respond to infection inside the body, but also on the surface, as in the case of skin infection

• After they die collect in the area of infection which causes pus to form

State the function of neutrophils

• Neutrophils contain large number of lysosomes

• They engulf and ingest pathogens

Describe how pathogens are ingested and digested by phagocytes

• Neutrophils bind attached to the antigen of the pathogen

• The pathogen is engulfed by endocytosis forming a phagosome

• Lysosomes fuse to the phagosomes to form a phagolysosome

• Hydrolytic enzymes such are lysins are released and the pathogen is digested

• The products that are broken down such as amino acids, glucose, fatty acids are absorbed to be used

• The unwanted products are removed from the cell by exocytosis

Describe the structure and role of monocytes

• Structure: They are a large whit blood cell with a kidney shaped nucleus

• Role: They travel around the blood to damaged tissue and they leave, they become macrophages

Describe macrophages and their role

• They are large WBCs made in bone marrow

• They mature in the lymph nodes

• Macrophages play an important role in initiating the specific responses to invading pathogens

• When macrophages engulfs a protein, it does not fully digest it. The antigens on its surface of the pathogen are saved and moved to a protein complex on the surface of the cell - This cell now becomes a antigen presenting cell

Describe and explain the role of Antigen-presenting cells(APCs)

• It exposes the antigen on its surface, so that other cells of the immune system can recognise the antigen

• The protein complex ensures that the APC is not not mistaken for a foreign cell and attacked by other phagocytes

• The antigen presenting cell moves around the body where it can come in contact with specific cells that can activate the full immune response

  • These are T and B lymphocytes

• Their role is to increase the chances that the antigen will come into contact with the B and T lymphocytes