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Activation et différenciation des cellules B
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Q1: How does a naive B cell become sensitized to an antigen?
Sensitization begins when a naive B cell encounters an antigen that binds to its B cell receptor (BCR) on the surface. The B cell then engulfs the antigen through receptor-mediated endocytosis, internalizing the antigen-BCR complex. Inside the cell, the antigen is processed into smaller peptide fragments and combined with MHC II molecules, which are transported to the B cell surface for display.
Q2: What role do Helper T cells play in B cell activation?
After sensitization, the B cell presents the antigen-MHC II complex to Helper T cells. When the Helper T cell's TCR binds to this complex, the Helper T cell releases cytokines as co-stimulatory signals that activate the B cell. This interaction is essential for triggering the B cell's proliferation and differentiation into effector and memory cells.
Q3: What happens during clonal expansion of activated B cells?
Upon activation by Helper T cell signals, the B cell undergoes clonal expansion, rapidly proliferating to generate many identical B cells capable of binding to the same antigen. This expansion amplifies the immune response by creating a large population of cells with identical antigen specificity, enabling a more effective defense against the pathogen.
Q4: How do plasma cells and memory B cells differ in function?
Some activated B cells differentiate into effector plasma cells, which produce antibodies that neutralize antigens or mark them for destruction by phagocytes. Other activated B cells become long-lived memory B cells that provide immunological memory, enabling rapid recognition and response upon future encounters with the same antigen.
Q5: What pathogens can B cells help defend against?
B cells mount tailored responses against specific pathogens including bacteria, free virus particles, toxins, and parasites. Through antibody production and antigen presentation, B cells enable the adaptive immune system to recognize and eliminate these diverse threats with precision and specificity.
Q6: Why is immunological memory important after B cell differentiation?
Memory B cells generated during initial antigen exposure provide immunological memory that enables faster and stronger responses to subsequent encounters with the same antigen. This long-lived population of cells allows the immune system to recognize previously encountered pathogens more quickly, providing enhanced protection against reinfection.
Q7: How does antigen processing contribute to B cell sensitization?
During sensitization, the internalized antigen is broken down into smaller peptide fragments and combined with MHC II molecules to form an antigen-MHC II complex. This processed complex is transported to the B cell surface where it is displayed, allowing the B cell to function as an antigen-presenting cell for Helper T cells and enabling proper immune activation.