B cells: Development, activation and humoral immunity Flashcards
B-cell development:
B cells develop in the bone marrow, where they undergo selection processes to ensure self-tolerance.
Bone marrow selection:
B cells that bind self-antigens with high affinity are eliminated to prevent autoimmunity.
B-cell receptor (BCR):
A membrane-bound antibody that allows B cells to recognize specific antigens.
Naïve B cells:
Mature B cells that have not yet encountered their specific antigen.
B-cell activation:
Occurs when the BCR binds to its specific antigen, and co-stimulatory signals from helper T cells are provided.
Helper T-cell support for B cells:
Activated CD4+ T cells provide cytokines and co-stimulatory signals that help B cells proliferate and differentiate.
Clonal expansion of B cells:
Activated B cells proliferate, creating a population of identical cells to combat the antigen.
B-cell differentiation:
Activated B cells differentiate into plasma cells (antibody-secreting cells) and memory B cells.
Plasma cells:
Differentiated B cells that secrete large amounts of antibodies specific to the antigen.
Antibody production:
Plasma cells produce antibodies (immunoglobulins) that bind to antigens, neutralize them, or mark them for destruction.
Humoral immunity:
The immune response mediated by antibodies produced by B cells, targeting pathogens and toxins.
Isotype switching:
B cells can change the class of antibody they produce (e.g., from IgM to IgG) in response to cytokine signals.
Memory B cells:
Long-lived B cells that remain after infection resolution, providing rapid antibody production upon re-exposure to the same antigen.
Antigen presentation by B cells:
B cells can act as antigen-presenting cells (APCs), presenting processed antigen to helper T cells to enhance activation.
T-independent activation:
Some antigens, like polysaccharides, can activate B cells without T cell help, though this response is weaker and lacks memory.
T-dependent activation:
Requires help from CD4+ T cells for full activation, leading to stronger antibody responses and memory formation.
IgM antibodies:
The first antibodies produced during an immune response, primarily produced by activated B cells.
IgG antibodies:
Antibodies produced after isotype switching, important for long-term immunity and pathogen neutralization.
IgA antibodies:
Found in mucosal areas, providing protection against pathogens entering through mucosal surfaces.
IgE antibodies:
Involved in allergic reactions and defense against parasitic infections.
Antibody affinity maturation:
During immune responses, B cells undergo mutations in their antibody genes, leading to higher-affinity antibodies.
Somatic hypermutation:
A process where mutations occur in the variable regions of the BCR genes, allowing B cells to produce antibodies with increased affinity for the antigen.
Follicular B cells:
B cells that reside in lymphoid follicles and are crucial for generating memory B cells and high-affinity antibodies.
Marginal zone B cells:
B cells found in the spleen that respond to blood-borne antigens and are involved in T-independent responses.
B-cell tolerance:
The process by which B cells are prevented from reacting against self-antigens, ensuring self-tolerance.
B-cell activation in secondary lymphoid organs:
Activated B cells undergo clonal expansion and differentiation in lymph nodes and spleen after encountering antigen.
Antibody-mediated immunity:
Antibodies bind to pathogens or toxins, neutralizing them or marking them for phagocytosis or complement activation.
Complement activation by antibodies:
Antibodies, particularly IgM and IgG, can activate the complement system, leading to pathogen destruction.
Opsonization:
Antibodies enhance phagocytosis by marking pathogens for recognition and engulfment by phagocytes.
Antibody-dependent cell-mediated cytotoxicity (ADCC):
Antibodies bound to target cells can recruit NK cells to destroy infected or tumor cells.
B-cell memory response:
Upon re-exposure to an antigen, memory B cells rapidly differentiate into plasma cells and secrete antibodies.
Humoral immunity and vaccines:
Vaccines stimulate the production of memory B cells and antibodies to provide long-term immunity against pathogens.
