B-cells

B-cells

B-cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They play a crucial role in the adaptive immune system by producing antibodies that are used to attack invading bacteria, viruses, and toxins.

Development

B-cells develop from hematopoietic stem cells in the bone marrow. The process of B-cell development involves several stages:

• Pro-B cells: These are the earliest B-cell precursors. They undergo heavy chain gene rearrangement.
• Pre-B cells: These cells express a pre-B cell receptor and undergo light chain gene rearrangement.
• Immature B cells: These cells express IgM on their surface.
• Mature B cells: These cells express both IgM and IgD and are capable of responding to antigens.

Activation

B-cells are activated in the lymph nodes and spleen when they encounter their specific antigen. Activation requires two signals:

1. Binding of the antigen to the B-cell receptor (BCR).
2. A second signal provided by helper T-cells or other means.

Upon activation, B-cells can differentiate into plasma cells or memory B-cells.

Functions

Antibody Production

The primary function of B-cells is to produce antibodies. Plasma cells, which are differentiated B-cells, secrete large quantities of antibodies that circulate in the blood and lymph.

Antigen Presentation

B-cells can also act as antigen-presenting cells (APCs). They internalize antigens, process them, and present them on their surface in association with MHC class II molecules to T-cells.

Memory B-cells

Memory B-cells are long-lived cells that provide rapid and robust antibody responses upon re-exposure to the same antigen.

Types of B-cells

• Follicular B-cells: These are the most common type of B-cells found in the lymphoid follicles of the spleen and lymph nodes.
• Marginal zone B-cells: These are found in the marginal zone of the spleen and are important for T-independent antigen responses.
• B-1 cells: These are a subset of B-cells that are primarily found in the peritoneal and pleural cavities and are involved in the production of natural antibodies.

Clinical Significance

B-cell Disorders

B-cells can be involved in various disorders, including:

• Autoimmune diseases: Such as systemic lupus erythematosus and rheumatoid arthritis, where B-cells produce autoantibodies.
• Immunodeficiencies: Such as X-linked agammaglobulinemia, where there is a lack of B-cells.
• B-cell lymphomas: Such as Hodgkin's lymphoma and non-Hodgkin's lymphoma, which are cancers of B-cells.

See Also

• T-cells
• Immune system
• Antibody

References

• Janeway, C. A., et al. Immunobiology: The Immune System in Health and Disease.
• Abbas, A. K., et al. Cellular and Molecular Immunology.