B Cell Development and Activation
- B cells originate from hematopoietic stem cells (HSCs) in the bone marrow.
- HSCs differentiate into multipotent progenitor (MPP) cells and then into common lymphoid progenitor (CLP) cells.
- B cell development occurs in stages, marked by gene expression patterns and rearrangements of immunoglobulin genes.
- Positive selection and negative selection processes ensure proper B cell development.
- Immature B cells migrate from the bone marrow to the spleen, passing through transitional stages.
- B cell activation occurs in secondary lymphoid organs like the spleen and lymph nodes.
- B cells are activated when they bind to antigens via their B cell receptors (BCRs).
- Different subsets of B cells undergo T cell-dependent or T cell-independent activation.
- CD21, in complex with CD19 and CD81, enhances B cell activation.
- T cell-dependent activation involves antigen uptake, presentation to T cells, and co-stimulation through CD40L.
T Cell-Dependent Activation and B Cell Differentiation
- T cell-dependent antigens require the help of T cells for B cell activation.
- B cells take up antigens, degrade them, and present peptide pieces to T cells.
- T helper cells recognize the peptide-MHC-II complexes through their T cell receptors (TCRs).
- T cell activation leads to the expression of CD40L and cytokines.
- CD40L binding to CD40 on B cells promotes proliferation, immunoglobulin class switching, and somatic hypermutation.
- Activated B cells undergo a two-step differentiation process.
- The extrafollicular response occurs outside lymphoid follicles.
- Activated B cells proliferate, undergo class switching, and differentiate into plasmablasts.
- In lymphoid follicles, B cells form germinal centers (GCs) for further differentiation.
- GCs facilitate proliferation, class switching, and affinity maturation, resulting in memory B cells and plasma cells.
B Cell Functions and Memory B Cell Activation
- B cells produce antibody molecules, which can be secreted or inserted into the plasma membrane.
- Activated B cells differentiate into plasmablasts or plasma cells that secrete antibodies.
- B cells present antigens and secrete cytokines.
- B cell receptors (BCRs) allow B cells to bind to foreign antigens and initiate an antibody response.
- B cells play a crucial role in humoral immunity and the adaptive immune system.
- Memory B cells are activated by detecting and binding their target antigen.
- Some memory B cells can be activated without T cell help, while others require T cell help.
- Memory B cells present the antigen to T cells through receptor-mediated endocytosis and MHC-II molecules.
- Memory T helper cells recognize and bind the MHC-II-peptide complexes.
- Memory B cells can differentiate into plasmablasts and plasma cells via an extrafollicular response or enter a germinal center reaction.
B Cell Types and B Cell-related Pathology
- Plasmablasts are short-lived, proliferating antibody-secreting cells.
- Plasma cells are long-lived, non-proliferating antibody-secreting cells.
- Lymphoplasmacytoid cells have features of both B lymphocytes and plasma cells.
- Memory B cells are dormant B cells that initiate a stronger antibody response upon re-encountering the antigen.
- B-2 cells are the most common type of B cells responsible for generating high-affinity antibodies.
- Autoimmune diseases can result from abnormal B cell recognition of self-antigens.
- B cell activity is correlated with disease activity in autoimmune diseases such as scleroderma, multiple sclerosis, and systemic lupus erythematosus.
- Malignant transformation of B cells can cause various cancers, including leukemia and lymphoma.
- Abnormal B cells may be observed in diseases such as diffuse large B-cell lymphomas.
- Patients with B cell alymphocytosis are more susceptible to infections.
Epigenetics and B Cell Development
- A study investigated the methylome of B cells along their differentiation cycle.
- Whole-genome bisulfite sequencing was used to analyze the DNA methylation patterns.
- Epigenetic changes in B cells can influence their differentiation and function.
- Understanding the epigenetic regulation of B cells may provide insights into immune-related diseases.
- Epigenetic modifications play a role in the development and maintenance of B cell identity.
B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or inserted into the plasma membrane where they serve as a part of B-cell receptors. When a naïve or memory B cell is activated by an antigen, it proliferates and differentiates into an antibody-secreting effector cell, known as a plasmablast or plasma cell. In addition, B cells present antigens (they are also classified as professional antigen-presenting cells, APCs) and secrete cytokines. In mammals, B cells mature in the bone marrow, which is at the core of most bones. In birds, B cells mature in the bursa of Fabricius, a lymphoid organ where they were first discovered by Chang and Glick, which is why the B stands for bursa and not bone marrow, as commonly believed.
| B lymphocyte cell | |
|---|---|
.jpg) Transmission electron micrograph of a human B cell | |
| Details | |
| System | Immune system |
| Identifiers | |
| Latin | lymphocytus B |
| MeSH | D001402 |
| FMA | 62869 |
| Anatomical terms of microanatomy | |
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B cells, unlike the other two classes of lymphocytes, T cells and natural killer cells, express B cell receptors (BCRs) on their cell membrane. BCRs allow the B cell to bind to a foreign antigen, against which it will initiate an antibody response. B cell receptors are extremely specific, with all BCRs on a B cell recognizing the same epitope.
