5 - B lymphocytes

Question 1

What condition arises as a result of lack of B and T lymphocytes?

Answer 1

SCID (severe combined immunodeficiency disease)

Question 2

Define antigen

Answer 2

proteins or molecules that induce an adaptive immune response

Question 3

What are the 2 types of adaptive immune response and how do lymphocytes fit into this?

Answer 3

humoral - B cells: antibodies

cellular - T-cells: cytokines and killing

Question 4

What are the opponents of the BCR?

Answer 4

membrane-anchored antibody and disulphite-linked heterodimers Igα and Igβ
(the cytoplasmic tails of the mIg are too sort to signal)
(the cytoplasmic tails of Igα/Igβ are long enough to intact with intracellular signalling molecules)

Question 5

What are the gene segments in the light and have chains of the BCR/antibody/immunoglobulin?

Answer 5

Light chain = V + J
Heavy chain = V + D + J

V = variable
D = diversity
J = joining

Question 6

For activation, B cells require co-stimulation. What is this called and what are the 2 pathways?

Answer 6

needs an accessory signal
This can come:
- directly from microbial constituents (T-cell independent pathway)
- from T-cells (T-cell dependent pathway)

Question 7

What happens after a T-cell recognises an antigen on the surface of B-cells (T-cell dependent pathway)?

Answer 7

they secrete lymphokines (cytokines)
the B-cells enter the cell cycle and develop into a clone of cells with identical BCRs (clonal selection)

NOTE: the type of cytokine produced depends on which T-helper cell bound (Th1 or 2) - different cytokines will switch the kind of constant region on the antibody