The Specific Immune Repsonse

Question 1

What is the specific immune response and when is it needed?

Answer 1

If phagocytes cannot eliminate the pathogen, then other WBCs are needed. These are T and B lymphocytes. T and B cells target specific antigens in the surface of the pathogen

Question 2

Is the specific immune response slow or fast and does it provide short term or long term immunity

Answer 2

Slow to respond at first but is very effective and provides long term immunity

Question 3

What are the stages of the cell mediated response?

Answer 3

1. A macrophage has engulfed and hydrolysed the pathogen and then presents the antigens of the pathogen on its cell surface membrane
2. Clonal Selection - T cells specific receptor proteins will bind to the complementary antigens being presented to it, this activates T cell
3. Clonal Expansion - activated T cell divides by mitosis and produces many clones
4. Clones differentiate to become either helper T cells or cytotoxic T cells

Helper T cells - release cytokines which stimulate phagocytes and also activate specific B cells to divide

Cytotoxic T cells - recognise infected body cells as the infected cells will have some to the pathogens antigens on its surface. The T cell receptor protein binds to these antigens and then they secrete a protein called perforin that makes holes in the cell surface membrane of the target cell. These holes mean the cell surface membrane because freely permeable to all substances and the cell dies along with any pathogens that may be in it.

Question 4

What are the stages of the humoral response?

Answer 4

1. B lymphocyte has a specific antibody which binds to the complementary antigen on pathogen surface
2. Pathogen enters the B cell by endocytosis and its antigens are presented on the surface of the B cell
3. Clonal Selection - Specific, activated helper T cells bind to the processed antigen on the B cell by releasing cytokines which activates the B cell
4. Clonal Expansion - B cell divides by mitosis forming clones
5. Clones cells differentiate into plasma B cells and memory B cells

Plasma B cells - produce + secrete antibodies into the blood (only survive for a few days)

Memory B cells - long lived cells that circulate the blood. If they encounter the same antigen they divide rapidly into plasma B cells and more memory B cells. Plasma B cells produce more antibodies, faster. This provides long term immunity.

Question 5

What is the difference between primary immune response and secondary immune response?

Answer 5

Primary = slower
• due to few B and T cells with the correct specificity for the particular antigens on the pathogen
• Takes time for the processes of Clonal expansion/selection to occur
• Eventually antibody levels will rise, however the delay can result in the person suffering symptoms as the pathogen has the opportunity to reproduce and produce toxins.
• Once the pathogen has been eliminated the blood antibody level falls while specific memory B and T cells will remain in the body

Secondary = faster
• if pathogen re invades body, memory B and T cells are rapidly activated
• takes little time for one of the many memory cells of the correct specificity to encounter antigen
• B memory cells divide rapidly to produce plasma B cells which results in more antibodies being produced and at a ** faster** rate than primary