The adaptive immune response, a sophisticated defense mechanism, relies on the activation and differentiation of B lymphocytes, or B cells. These processes enable our bodies to mount a tailored response against specific pathogens such as bacteria, free virus particles, toxins, and parasites.
When naive B cells encounter a specific antigen that can bind to the B cell receptor (BCR) on their surface, they undergo sensitization to respond to the antigen's presence. Sensitization begins with antigen recognition, causing the B cell to engulf the antigen through receptor-mediated endocytosis. Once inside the B cell, the antigen is broken down into smaller peptide fragments, which combine with MHC II molecules. This antigen-MHC II complex is then transported to the B cell surface, where it is displayed, completing the sensitization process.
After sensitization, the B cell acts as an antigen-presenting cell for T cells. The binding of the MHC II-complex antigen to the T cell receptor (TCR) on a Helper T cell releases cytokines, which serve as co-stimulatory signals to activate the B cell. Upon activation, the B cell undergoes clonal expansion, rapidly proliferating to generate identical B cells capable of binding to the same antigen. Some activated cells differentiate into effector plasma cells, producing antibodies. The antibodies can neutralize the antigen, preventing it from interacting with host cells or mark it for destruction by phagocytes. Simultaneously, other activated B cells differentiate into long-lived memory B cells that provide immunological memory upon subsequent encounters with the same antigen.
Naive B cells become sensitized when they encounter their corresponding antigen, which binds to the B cell receptor, or BCR, on the cell surface.
After binding, the B cell engulfs the antigen by receptor-mediated endocytosis, internalizing the antigen-BCR complex.
Inside the B cell, the antigen is processed into smaller peptide fragments and combined with MHC II molecules.
The antigen-MHC II complex is transported for display on the surface of the B cell, completing the sensitization process.
Next, the sensitized B cell binds the TCR on Helper T cells, which release cytokines as a co-stimulatory signal to activate the B cell.
Upon activation, the B cell undergoes clonal expansion, rapidly proliferating to generate identical B cells capable of binding to the same antigen.
Some activated cells differentiate into effector plasma cells, producing antibodies that neutralize the antigen or mark it for destruction.
Simultaneously, other activated B cells differentiate into long-lived memory B cells that provide immunological memory upon future encounters with the same antigen
繁體中文
