5.1 Defence mechanisms

Question 1

What are the two types of immune response?

Answer 1

-cell-mediated responses, which involve T-lymphocytes
-humoral responses, which involve B-lymphocytes

Question 2

How does the body distinguish self cells from foreign (non-self) bodies?

Answer 2

the proteins on the cell-surface membrane have highly specific tertiary structures, and that 3D shape is used by the immune system to identify the cell. this identification is the first stage of removing any threats

Question 3

How can cell recognition pose a problem for those with tissue or organ transplants, and how can this issue be controlled?

Answer 3

the immune system may recognise the transplanted tissues as non-self and attempt to destroy them. this can be limited by matching donor tissues to the recipient as closely as possible (e.g. from relatives) and by the recipient taking immunosuppressant drugs.

Question 4

What are four defence mechanisms?

Answer 4

(non-specific, which are immediately acting and same for all pathogens) physical barriers such as skin, and phagocytosis (5.2)
(specific, which is a slower response but specific to each pathogen) cell-mediated response by T-lymphocytes (5.3) and humoral response by B-lymphocytes (5.4)

Question 5

Why are there no lymphocytes in the body which attack self cells?

Answer 5

-as a fetus, infection is rare so lymphocytes in the body will almost exclusively with the body’s own material. any lymphocytes with receptors that fit self cells either die or are suppressed
-as an adult, lymphocytes are produced in the bone marrow and initially only encounter self-antigens. any lymphocytes which have an immune response to the self-antigens undergo programmed cell death (apoptosis) before they have the opportunity to differentiate into mature cells