Animal defences against pathogens - Specific

Question 1

What is a specific defence?

Answer 1

Where immune system recognises antigen on surface of pathogen + response is targeted to destroy that specific pathogen

Can take 14 days for effective response but memory of infection produced so next response is faster

Question 2

What are the 2 types of specific immunity + what lymphocytes do they involve?

Answer 2

Cell mediated immunity = T lymphocytes
Humoral immunity = B lymphocytes

Question 3

What is cell mediated immunity (CMI)?

Answer 3

Where T lymphocytes respond to cells of organism that have been changed - maybe due to virus infection, antigen processing, or mutation

Question 4

What is an antigen?

Answer 4

Recognition molecule + recognises self and foreign pathogens, usually proteins, on cell surface membrane

Question 5

Where are T lymphocytes made?

Answer 5

Made in bone marrow + mature in thymus gland

Surface has thousands of T lymphocyte receptors

Question 6

What happens in the presentation of antigen stage of cell mediated immunity (stage 1)?

Answer 6

• Phagocytosis = Takes proteins from surface of pathogen + presents them to other cells in immune system
• Macrophages engulf + digest these in phagocytosis + process anitgens from surface to form antigen-presenting cells (APCs)
• APC will have major histocompatibility complex (MHC) on surface that holds antigens

Question 7

What is a major histocompatibility complex?

Answer 7

Proteins, MHC 2 presents foreign antigen in a self molecule to T cell

Question 8

What happens in the signals + clonal selection stage of cell mediated immunity? (stage 2)

Answer 8

• T helper cells have surface receptor (CD4+) that recognises antigen presented by APC
• Releases interleukins + cytokines to activate specific T cell
• Activated T cell replicates via mitosis to produce clones, each have receptor that recognises antigen

Question 9

What happens in the clonal expansion stage of cell mediated immunity (stage 3)?

Answer 9

• Cloned T cells (from mitosis) all recognise antigen from pathogen

Cloned T cells can either:
- Stimulate development of killer T cells
- Produce interleukins to stimulate B cells
- Develop into memory T cells
- Produce interleukins to encourage more phagocytosis

Question 10

Why does it take 14 days?

Answer 10

Need to find matching receptors due to there being 1000s of T cell receptors

Question 11

What does humoral immunity do?

Answer 11

Responds to antigens + produces antibodies (proteins) that are soluble in blood + tissue fluid

Question 12

What are B lymphocytes?

Answer 12

Made + mature in bone marrow, found in lymph glands + free in tissues

Globular receptor proteins on surface membrane, identical to antibodies produced

Question 13

What are all antibodies called?

Answer 13

Immunoglobulins, attached to membrane

Question 14

What are the first 3 stages of humoral immunity?

Answer 14

1. Activated T helper cells bind to B cell APC - clonal selection
2. Interleukins produced by activated T helper cells activate the B cells
3. Activated B cells divides by mitosis to give clones of plasma cells + B memory cells - clonal expansion

Question 15

What are the last 3 stages of humoral immunity?

Answer 15

4. Cloned plasma cells produce antibodies that fit antigens, bind to them, + diasble them - Primary immune response, can take days/weeks to be effective
5. Some cloned B cells debelop into B memory cells = If body infected by same patjogen again, B memory cells divide quickly to form plasma cell clones
6. Plasma cell clones = Produce right antibody + wipe out pathogen quickly, before it causes symptoms - Secondary immune response