3.6 Specific Celluar Defences Against Pathogens

Question 1

Lymphocytes

Answer 1

The white blood cells involved in the specific immune response.
Lymphocytes have a single type of membrane receptor which is specific for one antigen.
Lymphocytes are responsible for a specific response to foreign antigens and come in T and B forms.

Question 2

Repeated Division of the Lymphocyte

Answer 2

An antigen binding their specific lymphocyte receptor leads to repeated division of the lymphocyte, resulting in a clonal population of lymphocytes.

Question 3

Antigens

Answer 3

Molecules (often proteins) located on the surface of cells that trigger a specific immune response.

Question 4

Role of T Lymphocytes

Answer 4

T lymphocytes play a vital role in the immune system and account
for more than 80% of circulating lymphocytes.
They can differentiate between self and non-self antigens using their receptors. When a T lymphocyte receptor binds with a matching antigen on a pathogen, it is immediately triggered to divide
rapidly.
Cells that have become infected by a pathogen, will display the
pathogen antigens on their surface. T lymphocytes attach onto these
infected cells (receptor and antigen combine) and release proteins.
These proteins diffuse into the infected cells causing them to produce self-destructive enzymes which cause cell death (APOPTOSIS).

Question 5

Auto Immune Disease

Answer 5

A failure by T lymphocytes to recognise self-antigens.
This causes T lymphocytes to attack the body’s own cells.

Question 6

B Lymphocytes

Answer 6

Produce specific antibodies that recognise specific antigens.

Question 7

Antibodies

Answer 7

Y-shaped proteins that have receptor binding sites specific to a particular antigen on a pathogen.

Question 8

Antigen-Antibody Complex

Answer 8

Antibodies become bound to antigens, inactivating the pathogen. The resulting antigen-antibody complex can then be destroyed by phagocytosis.

Question 9

Allergy

Answer 9

An allergy is when B lymphocytes respond to antigens on substances that are harmless to the body.

Question 10

Memory Cells

Answer 10

Some B and T lymphocytes survive long term as memory cells.

Question 11

Secondary Exposure

Answer 11

When secondary exposure to the same antigen occurs, memory cells can rapidly give rise to a new clone of specific lymphocytes. These destroy the invading pathogens before the individual shows symptoms.

Question 12

HIV

Answer 12

HIV directly attacks and destroys T Lymphocytes. This causes depletion of T Lymphocytes which leads to the development of AIDS.

Question 13

Consequence of AIDS

Answer 13

Individuals with AIDS have a weakened immune system and so are more vulnerable to opportunistic infections.