Immunology - B and T cells

Question 1

Describe the process that B cells undergo to become long lived activated antibody producing plasma cells from naive immature B cells. Include details about how activation occurs, the other cells the B cell may interact with and the location of each stage in the activation process (5)

Answer 1

Naive immature B cells from the bone marrow migrate to the periphery (or spleen or lymph node) where they mature [1]

The B cell is activated upon encountering antigen in the spleen (or Lymph node) via the B cell antigen receptor [1]

The activated B cells form/enter germinal centres which are areas of high proliferation and hypermutation [1]

Interaction with and co-stimulation by CD4 T cells activates the B cells to promote isotype/class/Ig switching [1]

These activated B cells become plasma cells that secrete high-affinity antibody in the germinal centre/periphery/or migrate back to the bone marrow [1]

Question 2

Name the multipotent stem cell from which all cells of the immune system are generated (½)

Answer 2

Haematopoietic stem cell

Question 3

State the mechanism by which normal B cells die when they fail to mature in the bone marrow (½)

Answer 3

Apoptosis

Question 4

State which B cell receptor is found on mature B cells (1)

Answer 4

IgD or IgM (½ for Ig and ½ for the correct isotype)

Question 5

Name two (2) circulatory systems where B cells perform their immune surveillance role (1)

Answer 5

Blood (½) & lymphatic system (½)

Question 6

Name the type of cell that provides the additional signal required for full antibody production once B cells encounter a foreign antigen (½)

Answer 6

T helper cell

Question 7

Outline the key stages in a T cell dependent B cell response to an antigen (5)

Answer 7

B cells encounter antigen (1) and move to T zone in spleen or lymph node (1)

Naive T cells primed by direct interaction with dendritic cells (1)

Primed T cells interact with Antigen- activated B cells (1) in the T zone (0.5)

B cells develop into either plasma cells (1) in the medulla (0.5)

Or Memory B cells which produce high affinity antibody in response to antigen encounter (1.5) in the germinal centre (0.5

Question 8

Name the cell type that mediates B cell differentiation (½)

Answer 8

Stromal cell

Question 9

Name four (4) of the secreted or surface molecules that this cell expresses to direct B cell differentiation (2)

Answer 9

Surface: VCAM, CAM, FTL3. Secreted: CXCL12, IL3,4,7, GCSF or GMCSF

Question 10

Name the T helper cell type and cytokines important in directing an antibody response toward extracellular pathogens (1)

Answer 10

Th2 & IL4, IL-5, or IL-13

Question 11

List three (3) functions of antibody produced by B cells which are important for protection against infections that may be impaired in B cell deficient states (1½)

Answer 11

Opsonisation, Neutralisation, Complement activation, FcR mediated phagocytosis

Question 12

Outline the most likely source of her infection in this situation (1)

Answer 12

Her skin via her catheter i.e. breach in innate immunity

Question 13

Name the test that is performed on them to determine their eligibility and explain its importance (1½)

Answer 13

HLA typing to prevent graft versus host disease or to prevent the T cells in the bone marrow from seeing the recipient as foreign and mounting an immune response against it.

Question 14

The bone marrow donor was CMV positive and the patient was CMV negative. Name the specific cell involved in death of CMV-infected cells (½)

Answer 14

.