Immunology B Lymphocytes

Question 1

What is the adaptive immune response?

Answer 1

 B lymphocytes operate during the adaptive immune response
 Develops after encounter of antigen
 Takes 4-7 days to develop and become effective
 Elicited antibody production specific to encountered antigen
 2 types:
Humoral- B cells – antibodies
Cell Medicated- T cells – cytokines, lysis of pathogens

Question 2

What are B lymphocytes and where do they come from?

Answer 2

• White blood cells
• Derived from haemopoietic stem cells
• Are effector cells of humoral immunity; they secrete antibodies and form memory cells

Where do they come from?

• Derived in the bone marrow in the absence of antigens
• Mature in the bone marrow, whereby they express specific B cell receptors (BCR)
• Migrate into the circulation (blood, lymphatic system) and into lymphoid tissues
• Antibody production requires antigen-induced B cell activation and differentiation- this occurs in peripheral
lymphoid organs

Question 3

What is the process of B lymphocyte maturation?

Answer 3

• Pro-B Cell -> Pre-B Cell -> Immature B Cell -> Mature B Cell
• Occurs in the bone marrow in the absence of antigen
• Mature B cells are specific for a particular antigen- their specificity
resides in B cell receptor (BCR); a membrane bound immunoglobulin

Question 4

Describe in more detail, the B cell receptor.

Answer 4

• Transmembrane protein complex composed of:

 mIg
- central larger immunoglobulin molecule
- cytoplasmic tail too short so is not involved in signalling

 Igα/Igβ
- di-sulfate linked heterodimers
- contain immunoglobulin-fold structure
- cytoplasmic tails of Igα/Igβ is long enough to interact with intracellular
signalling molecules
• has a unique binding site- binds to ANTIGENIC DETERMINANT or
EPITOPE -made before the cell ever encounters antigen
• large monoclonal population on surface of the B lymphocyte

Question 4

What is Antigen and B- lymphocyte Cell Receptor Diversity?

Answer 4

• For the immune system to respond to the large number of antigens we are exposed to, we need to have a large REPERTOIRE of specific BCR on different B cells that can recognise the huge array of antigens
• 1010 different antibody molecules can be generated by B cells with specific BCR
• Functional BCR genes do not exist until they are generated during lymphocyte development
• Each BCR chain (κ & λ light chains, and heavy chain) is encoded by separate MULTIGENE FAMILIES ON
DIFFERENT CHROMOSOMES
• During maturation, these gene segments are rearranged and brought together to form the BCR –
IMMUNOGLOBULIN GENE REARRANGEMENT
• There are a number of VARIABLE; V, DIVERSITY;D and JOINING;J gene segments that may be responsible for
each chain. The Diversity segment is only associated with the heavy chain. There is also a CONSTANT REGION associated with each chain
• This generates the diversity of the lymphocyte repertoire

Question 5

What is mean by prototypical membrane protein synthesis?

Answer 5

• Genomic DNA – (transcription) – Primary transcript RNA/pre-mRNA – (Splicing) – Mature mRNA – (translation) – Membrane protein
• Intracellular; Amino terminus of protein and protein domains relating to specific exons
• Transmembrane; relates to specific exon/s
• Extracellular; cytoplasmic tail- consists of exons and carboxyl terminus