Lecture 05: Antibody Production and Adaptive Immunity [SEQ 2]

BCRs recognize a wide variety of antigens, including carbohydrates, lipids, DNA, and proteins, directly. They have two antigen-binding sites formed by the pairing of heavy and light chains. In contrast, TCRs only recognize peptide antigens presented by cells in complex with MHC molecules. TCRs have a single binding site formed by the alpha and beta chains. This difference reflects the distinct roles of B cells and T cells in the immune response.

When an antigen enters the lymph nodes, it encounters naive B cells with diverse BCRs. Clonal selection occurs when a specific B cell with a BCR that recognizes the antigen is activated. This activated B cell undergoes rapid replication, producing clones of itself. These clones differentiate into plasma cells, which secrete large quantities of antibodies specific to that antigen, and memory cells, which provide long-term immunity. Clonal selection ensures that only B cells specific to a particular antigen are activated and amplified, leading to a highly targeted immune response and a diverse antibody repertoire.

Plasma cells are short-lived cells that secrete large quantities of antibodies, providing immediate protection against an ongoing infection. Memory B cells are long-lived cells that retain the same BCR as the activated parent B cell. Upon re-exposure to the same antigen, memory B cells rapidly differentiate into plasma cells, producing a large number of antibodies, leading to a faster and more effective response, often preventing disease symptoms. This provides long-term immunity against pathogens that are encountered previously.

<p>Vaccines introduce a weakened or inactive form of a pathogen or its components into the body. This triggers an immune response, including B-cell activation and clonal selection, without causing the full-blown disease. This process generates memory B cells specific to the vaccine-associated antigens. When exposed to the actual pathogen, these memory B cells rapidly differentiate into plasma cells, producing antibodies that neutralize the infection before it causes illness. This provides long-lasting protection against the disease.</p> Signup and view all the answers

<p>B cells mediate humoral immunity by producing antibodies that directly target extracellular pathogens and toxins. They recognize a wide range of antigens and contribute to neutralizing and eliminating pathogens. T cells, involved in cell-mediated immunity, target infected cells or abnormal cells. They recognize peptide antigens presented by MHC molecules on the surface of cells. They directly kill infected cells or activate other immune cells to eliminate the threat. Together, they provide a comprehensive immune response that targets both extracellular and intracellular threats, ensuring effective protection against pathogens.</p> Signup and view all the answers

<p>During differentiation in the bone marrow, each B cell undergoes genetic recombination to create its own unique antibody gene. This involves rearranging segments of the antibody gene on the chromosome, specifically the variable (V), joining (J), and diversity (D) segments for the heavy chain, and V and J segments for the light chain. This combinatorial diversity, alongside junctional diversity (random mutations at the segment junctions), ensures each B cell produces a distinct antibody capable of recognizing a specific antigen.</p> Signup and view all the answers

<p>The adaptive immune system ‘remembers’ previous encounters with pathogens through memory B cells. When a B cell encounters its specific antigen, it proliferates and differentiates, creating both effector B cells that produce antibodies to combat the current infection and memory B cells. These memory B cells persist long-term, ready to rapidly mount a more robust immune response if the same pathogen is encountered again. This allows for a faster and more efficient response to subsequent infections from the same pathogen.</p> Signup and view all the answers

<p>The two main arms of the adaptive immune response are the humoral response and the cell-mediated response. The humoral response relies on antibodies produced by B cells, which target pathogens in the body fluids. The cell-mediated response, however, involves T cells directly attacking infected cells or destroying pathogens through the release of cytotoxic molecules. The humoral response primarily defends against extracellular pathogens, while the cell-mediated response targets intracellular pathogens and eliminates infected cells.</p> Signup and view all the answers

<p>Dendritic cells (DCs) act as sentinels in external-facing tissues, equipped with pathogen recognition receptors (PRRs) to detect invading microbes. Upon encountering pathogens and cytokines, DCs become activated and migrate to lymph nodes. They present processed antigens to naive T cells and B cells, initiating the adaptive immune response. DCs possess long cytoplasmic projections called dendrites, which enhance their ability to capture and present antigens, and their unique migratory properties enable them to bridge the gap between innate and adaptive immunity.</p> Signup and view all the answers

<p>Antibody affinity maturation is an ongoing process of mutation and selection that occurs in the variable region of antibodies produced by B cells. It involves the introduction of random mutations in the variable region of antibodies during a B cell's proliferation. These mutations are followed by a selection process where B cells with higher affinity for the antigen survive and proliferate, while those with lower affinity are eliminated. This process results in a gradual increase in the affinity of antibodies for their target antigen over time, ultimately leading to a more effective immune response.</p> Signup and view all the answers

<p>A naive B cell is a B cell that has not yet encountered its specific antigen. It expresses IgD as its B-cell receptor, but has not yet undergone proliferation or differentiation. Upon encountering its antigen, a naive B cell becomes activated. This activation involves: 1) binding to the antigen via its B-cell receptor, 2) receiving signals from helper T cells, and 3) undergoing clonal expansion through proliferation. Activated B cells differentiate into plasma cells, which produce and secrete antibodies, and memory B cells, which provide long-lasting immunity.</p> Signup and view all the answers

<p>The lymphatic system is a network of vessels that carries lymph fluid throughout the body, driven by muscle movement. This fluid carries antigens from the tissues to lymph nodes, where they are presented to immune cells. Within the lymph nodes, dendritic cells and macrophages display processed antigens to naive B cells and T cells, initiating the adaptive immune response. The lymphatic system, therefore, plays a vital role in ensuring that antigens are efficiently transported to the immune system for recognition and response.</p> Signup and view all the answers

White blood cells produced in the bone marrow that create antibodies.

The variety of antibodies generated through genetic recombination of V, J, and D segments.

Variable region of an antibody that differs among different antibodies.

Continuous mutations in an antibody that increase affinity to the antigen.

Immune response that retains memory of past infections, developed by B and T cells.

Antigen-presenting cells that migrate to lymph nodes after engulfing pathogens.

Network that transports lymph fluid through the body and is involved in immune responses.

The aspect of immunity that involves antibodies produced by B cells.

Membrane-bound antibody on B-cells that recognizes antigens like carbohydrates, lipids, and proteins.

Process by which B-cells are activated by antigens, replicating to form clones.

B-cells that provide long-lasting immunity by responding quickly to previous antigens.