Week 3 : Infection and Immunity

Question 1

Define a virus.

Answer 1

Microscopic, intracellular parasites that contain either a DNA or RNA genome surrounded by a protective protein coat (capsid) that can infect cells and cause disease.

Question 2

What are the two main jobs of the immune system?

Answer 2

• To defend the body against microbes (viruses), fungi and parasites
• To be tolerant to the healthy microbes, to food and to itself.

Question 3

List 2 examples of physical barriers.

Answer 3

• Structure of the organ lining
• Cilia

Question 4

List 2 examples of chemical barriers.

Answer 4

• Mucus
• Antimicrobial peptides (peptides are small proteins; e.g. tears are packed with lysozyme; sweaty armpits are rich in defensins)

Question 5

List the 2 types of acquired immunity.

Answer 5

• Humoral immunity
• Cell mediated immunity

Question 6

What are the features of humoral immunity?

Answer 6

• involves B-cells
• produces antibodies
• helps T cells

Question 7

What are the features of cell mediated immunity?

Answer 7

• involves T cells
• involves direct contact
• cytotoxic T cells crucial for killing pathogens/cancer cells

Question 8

State the 6 stages of humoral immunity.

Answer 8

1.Inflammation
2.Phagocytosis
3.Antigen presentation
4. Antigen recognition
5. Clonal expansion
6. Antibody release

Question 9

What is clonal selection?

Answer 9

When antigen presenting cells (APCs) leave tissues and move to lymph nodes where they secrete appropriate cytokines to attract naïve T cells which upon command differentiate into helper T cells.

Question 10

What are the 3 steps of clonal expansion?

Answer 10

1.The cytokines produced by the T-helper cell cause the bound B-lymphocytes to divide.
2.Some of the B-lymphocytes form memory cells which migrate to the lymph nodes.
3.The remaining B-lymphocytes circulate in the blood plasma and become plasma cells, producing antibodies.

Question 11

List the 4 main ways an antibody can neutralise an antigen.

Answer 11

• Agglutination
• Antitoxins
• Lysis
• Opsonisation

Question 12

What is agglutination?

Answer 12

The clumping of pathogens together, immobilising them.

Question 13

What do antitoxins do?

Answer 13

They bind to toxins released by the pathogen, preventing them from harming cells .

Question 14

What is lysis?

Answer 14

The disintegration of a cell by the rupture of a cell wall or membrane.

Question 15

What is opsonisation?

Answer 15

Immune process which uses opsonins to label foreign pathogens for elimination by phagocytes.