2.5.7 The B lymphocyte Response

Key Features of B Cells:

1. Development and Maturation:

• B cells are produced and mature in the bone marrow.
• Each B cell has a specific receptor (BCR) on its surface, which binds to a complementary antigen.

2. Role in Humoral Immunity:

• B cells are responsible for producing antibodies that neutralise pathogens or mark them for destruction.

Steps in the B Lymphocyte Response:

3. Antigen Detection:

• A specific antigen binds to the B cell receptor (BCR) on a complementary B cell.
• The B cell engulfs the pathogen through endocytosis and processes the antigen.

4. Antigen Presentation:

• The processed antigen is displayed on the surface of the B cell bound to an MHC class II molecule.
• This converts the B cell into an antigen-presenting cell (APC).

5. Activation by Helper T Cells:

• Helper T cells (Tᕼ) recognise the antigen-MHC complex on the B cell and release cytokines.
• These cytokines stimulate the B cell to divide and differentiate.

6. Clonal Expansion:

• The activated B cell divides by mitosis, producing a large population of identical cells (clones) specific to the antigen.

7. Differentiation:

• Cloned B cells differentiate into:
• Plasma cells:
• Produce and release large quantities of antibodies specific to the antigen.
• Antibodies neutralise pathogens, clump them together (agglutination), or mark them for destruction by phagocytes.
• Memory B cells:
• Persist in the body, enabling a faster and stronger response to the same antigen during future infections (immunological memory).

Key Characteristics of the B Lymphocyte Response:

8. Specificity:

• Each B cell has a receptor specific to a single antigen, ensuring a targeted response.

9. Production of Antibodies:

• Antibodies are proteins that bind specifically to antigens, aiding in the elimination of pathogens.

10. Immunological Memory:

• Memory B cells remain in the body long-term, providing protection against re-infection.

Importance of the B Lymphocyte Response:

11. Neutralisation of Pathogens:

• Antibodies prevent pathogens from entering cells or neutralise their toxins.

12. Targeting Extracellular Pathogens:

• Particularly effective against bacteria, viruses, and fungi in body fluids.

13. Long-Term Immunity:

• Vaccination relies on the formation of memory B cells to provide immunity against specific diseases.