Paper 1 - Immune Response

Question 1

Phagocytosis

Answer 1

1. Phagocyte receptors bind to foreign antigens on surface of pathogen.
2. The phagocyte engulfs pathogen by endocytosis,.
3. The pathogen is contained in the phagocytic vesicle.
4. Lysosomes fuses with vesicle and lyzozymes (hydrolytic enzymes) digest the pathogen.
5. The phagocyte presents antigens on cell-surface membrane - becomes an antigen-presenting cell.

Question 2

Cell mediated response

Answer 2

1. Helper T cell with complimentary reception to antigen on phagocyte bind
2. T cell becomes activated and rapidly divides by mitosis into 3 types of T cell:

    - Cytotoxic (killer T cells) kills pathogens 
    - Helper T cells release cytokines that stimulate more phagocytes, B cells and killer T cells.
    - Memory T cells recognise antigen and enable a rapid response

Question 3

Humoral response

Answer 3

1. B cell has antibodies on membrane.
2. B cell with complimentary antibody and antigen binds and is activated by helper T cell.
3. B cell divides rapidly by clonal selection and produces 2 types of B cell:

   - Memory B cells divide rapidly and produce correct antibody in the secondary immune response if pathogen re-enters the body.
   - Plasma B cells rapidly secrete monoclonal antibodies complimentary to the antigens = agglutination of pathogens and stimulates phagocytosis.

Question 4

How vaccines lead to antibody production

Answer 4

1. Vaccine contains antigen from pathogen.
2. Phagocyte engulfs and digests pathogen and presents antigen on surface.
3. Helper T cell with complimentary receptor binds to antigen and is activated.
4. Helper T cell activates a B cell with complimentary antibody on surface.
5. B cells undergo clonal selection, produces plasma cells that secrete monoclonal antibodies or plasma cells.

Question 5

Direct ELISA TEST

Answer 5

1. Antigens from patient sample were stuck to bottom of well.
2. Monoclonal antibody with enzyme attached is added - binding site of this is complimentary to antigen so will bid if antigen is present.
3. Wash to remove unbound monoclonal antibody
4. Colourless substrate us added - if monoclonal antibody is bound and present enzyme attached to substrate will produce a coloured solution.

Question 6

Indirect ELISA TEST

Answer 6

1. Antigens are immobilised at bottom of well
2. Patient sample of antibodies is added - if antibody is present it will bind to complimentary antigen.
3. A secondary monoclonal antibody complimentary to the patients antibody is added with an enzyme attached - if antibody is present the secondary mAB will bind to it
4. Wash to remove unbound antibodies
5. Colourless solution is added - if antibodies present = coloured.

Question 7

HIV replication

Answer 7

1. Attachment proteins on HIV attach T complimentary receptors on helper T cell.
2. RNA enters cell
3. Reverse transcriptase converts RNA to DNA which is transcribed and translated by T helper cells ribosomes
4. Viral proteins produced.
5. Virus assembled and released from the T helper cell, destroying the cell.