1st and 3rd lines of defence

Question 1

The first line of defence

Answer 1

• The skin provides a formidable physical barrier to the entry of pathogens
• Healthy skin is rarely penetrated by microorganisms
• Certain chemical secretions are produced by the skin that inhibit the growth of bacteria and fungi
• Tears, mucus and saliva help to wash bacteria away

Question 2

Antibody production
How does the adaptive immune response function?
What are antibodies made of and how do they work?

Answer 2

• The adaptive immune response reacts by producing proteins called antibodies or immunoglobulins which are each specific to a particular antigen
• Antibodies are made up of 4 polypeptide chains, two light and two heavy, with two antigen binding sites at the tips
• Each type of antibody will identify a unique antigenic fragment, making this interaction specific.

Question 3

Humoral immunity
What is humoral immunity and what are B cells?
What happens when B cells are presented to macrophages?

Answer 3

• Humoral immunity describes the production of antibodies by B lymphocyte cells. B cells are antibody producing cells that develop in the bone marrow and only recognise one type of antigen.
• When antigens are presented to B cells (and helper T cells) by macrophages, the particular B cells will become activated and clone
• The majority of the cloned cells will be plasma B cells but a minority’s will be memory B cells

Question 4

Cell mediated response

Answer 4

Cell mediated immunity describes the activation of humoral immunity by helper T cells and the targeted destruction of infected cells by cytotoxic T cells.
- Note that humoral immunity will not occur without activation from cell mediated immunity.

Question 5

Helper T Lymphocytes (helper T cells)
What happens when a pathogen encounters a macrophage?
What do helper T cells do and what do they activate?

Answer 5

• When a pathogen invades the body, it is engulfed by macrophages which present the antigenic fragments on its surface.
• This macrophage becomes an antigen presenting cell, and presents the antigen to helper T cells
• The helper T cells bind to the antigen and become activated and in turn activate B cells with the specific antibody for the antigen.
• The B cells clone plasma cells and memory B cells

Question 6

Cytotoxic T lymphocytes (cytotoxic T cells)

What do they recognise and do?

Answer 6

Cytotoxic T cells recognise antigenic fragments on infected cells (MHC-1 markers) and kill these cells before they replicate

• Some cytotoxic T cells can even kill types of cancer cells
• Cytotoxic T cells destroy your own infected cells by cell lysis, (the break down of cell wall and membrane) by releasing the toxin, perforin

Question 7

Plasma and memory B cells

Answer 7

Plasma B cells - mass produce and release antibodies

Memory B cells - remain to give long term immunity to the specific pathogen.