4.1.5: Secondary non-specific defences

Question 1

What are secondary defences used to combat?

Answer 1

Pathogens that have entered the body.

Question 2

Why is a pathogen recognised as foreign when it invades the body.

Answer 2

By the chemical markers on its outer membrane called antigens.

Question 3

What is an antigen?

Answer 3

Proteins or glycoproteins that are intrinsic to the plasma membrane. Antigens are specific to the organism.

Question 4

Why don’t antigens on our own cells produce a response?

Answer 4

Because they are recognised as our own.

Question 5

What are opsonins and how specific are they?

Answer 5

• Protein molecules that attach to the antigens on the surface of a pathogen. They are a type of antibody.
• Some opsonins are not very specific so they can attach to a variety of pathogenic cells.

Question 6

What is the role of the opsonin?

Answer 6

To enhance the ability of phagocytic cells to bind and engulf the pathogen.

Question 7

What is the first line of secondary defense?

Answer 7

Phagocytosis.

Question 8

What are the most common phagocytes and how can you recognise them?

Answer 8

• Neutrophils.

- They have a multi-lobed nucleus.

Question 9

Where are neutrophils manufactured, where do they travel?

Answer 9

In the bone marrow and they travel in the blood and often squeeze out of the blood into the tissue fluid.

Question 10

What do neutrophils contain?

Answer 10

Large numbers of lysosomes.

Question 11

Describe the process of phagocytosis.

Answer 11

1) Neutrophil binds to the opsonin attached to the antigen on the pathogen.
2) The pathogen is engulfed by endocytosis forming a phagosome.
3) Lysosomes fuse to the phagosome and release hydrolytic enzymes into it.
4) After digestion, the harmless products can be absorbed into the cell.

Question 12

What are macrophages?

Answer 12

Larger cells made in the bone marrow. They travel in the blood as monocytes before settling in the body tissues.

Question 13

Where are many monocytes found and what happens to them here?

Answer 13

In the lymph nodes where they mature into macrophages.

Question 14

what are dendritic cells and where are they found?

Answer 14

They are a type of macrophage and they are found in the more peripheral tissues.

Question 15

What is the role of macrophages?

Answer 15

Initiating the specific response to invading pathogens.

Question 16

What happens when a macrophage engulfs a pathogen?

Answer 16

• It does not fully digest it, the antigen from the surface of the pathogen is saved and moved to a special protein complex on the surface of the cell.
• The cell becomes an antigen presenting cell. It exposes the antigen on its surface, so that the other cells in the immune system can recognise the antigen.

Question 17

Why are antigen presenting cells not mistaken for foreign cells and attacked by other phagocytes?

Answer 17

The special protein complex prevents this from happening.

Question 18

How does antigen presentation activate the full immune response?

Answer 18

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

Question 19

What are the cells that activate the full immune response?

Answer 19

T-lymphocytes and B-lymphocytes.

Question 20

There may only be one T cell and one B cell with the correct antigen recognition site for the antigen, why does this make antigen-presenting cells important?

Answer 20

Because antigen-presenting cells increase the chances that the antigen will come into contact with the correct T cells and B cells.

Question 21

What is the activation of specific T and B cells called?

Answer 21

Clonal selection