B2 W1 - Adaptive Immunity Flashcards
(38 cards)
What are the two main branches of the immune system, and how do they interact?
The immune system comprises the innate and adaptive branches. The innate system often triggers and shapes the adaptive response, while the adaptive system can also provide feedback to enhance innate immunity.
How do the innate and adaptive immune systems differ in terms of evolutionary history and speed of response?
The innate system is evolutionarily older and provides a rapid, non-specific response. The adaptive systemis more recent, providing a slower but highly specific and targeted response.
What are the two main effector mechanisms found in both the innate and adaptive immune responses?
Both immune branches employ cell-mediated and humoral mechanisms. Cell-mediated immunity involves direct cell-to-cell interactions, while humoral immunity is mediated by soluble molecules.
What is the role of cell surface receptors in immune responses, and in which branch are they particularly important?
Cell surface receptors are crucial for recognizing and responding to specific threats. They are particularly vital for the adaptive immune response, where highly specific receptors on B and T cells recognize distinct antigens.
What are the two main types of lymphocytes involved in the adaptive immune response, and what key ability do they share?
The two main types of lymphocytes are B lymphocytes (B cells) and T lymphocytes (T cells). Both B cells and T cells possess receptors on their surface that can recognise and bind to specific antigens.
Where do T cells mature, and how does this relate to their name?
T cells migrate to and mature in the thymus, which is why they are called T cells. This process ensures they develop the ability to recognise specific antigens.
Where do mature lymphocytes reside and what triggers them to mount an immune response?
Mature T and B cells reside in peripheral lymphoid organs. When they encounter their specific cognate antigen, they become activated and initiate an immune response.
How do B cells and cytotoxic T cells differ in their methods of combating pathogens?
B cells, when activated by an antigen, differentiate into plasma cells that produce and secrete antibodies. These antibodies target pathogens in body fluids. Cytotoxic T cells directly kill infected or cancerous cells by releasing cytotoxic molecules.
What is the role of helper T cells in the adaptive immune response?
Helper T cells secrete signalling molecules called cytokines that stimulate and coordinate other immune cells, including B cells, cytotoxic T cells and macrophages. This “help” is often crucial for the full activation and effectiveness of other immune cells.
What is the function of regulatory T cells in the immune system?
Regulatory T cells (T-regs) have a suppressive or downregulatory effect on immune responses. This helps to prevent excessive immune activation and maintain immune system balance, protecting against autoimmunity.
Besides B and T cells, what other cell type plays a crucial role in activating the adaptive immune response?
Antigen presenting cells (APCs), such as dendritic cells and macrophages, engulf foreign material, break it down, and present fragments (antigens) on their surface using MHC molecules to activate T cells.
What are memory cells and how do they contribute to long-term immunity?
Memory cells are long-lived B or T lymphocytes that persist in the body after an initial immune response. Upon subsequent encounters with the same antigen, memory cells enable a faster and more robust response, providing long-term immunity against specific pathogens.
How does the adaptive immune system achieve the ability to potentially detect any antigen?
The adaptive immune system generates a vast diversity of B cells, each with a unique immunoglobulin receptor on its surface. This enormous repertoire of receptors, theoretically, allows for the recognition of any antigen that the body might encounter.
How does the body regulate the immune response to prevent harmful reactions against itself (autoimmunity) and enhance responses against genuine threats?
The body controls the immune response by regulating the populations of B and T cells. Cells with receptors that recognise “self” antigens are eliminated to prevent autoimmunity. In contrast, cells with receptors that bind to foreign antigens are stimulated to proliferate and mount a targeted immune response.
What is meant by humoral immunity, and what is its primary effector molecule?
Humoral immunity refers to the immune response mediated by molecules in extracellular fluids, primarily antibodies (also known as immunoglobulins).
How does the B cell receptor relate to the antibodies produced by activated B cells?
The B cell receptor is a membrane-bound form of the antibody. Upon activation, the B cell differentiates into a plasma cell and secretes a soluble form of the same antibody that was initially present on its surface.
How does the activation of a B cell lead to changes in its morphology and function?
When an antigen binds to the B cell receptor, it triggers a signalling cascade within the cell. This leads to changes in gene expression, resulting in the development of extensive endoplasmic reticulum needed for producing and secreting large amounts of soluble antibodies. The activated B cell transforms into a plasma cell, essentially becoming an “antibody factory.”
What is clonal selection, and how does it ensure a targeted and effective humoral immune response?
Clonal selection is the process where a B cell that encounters and binds its cognate antigen is selectively stimulated to proliferate. This results in the production of a large clone of identical B cells, all producing the same antibody specific for the triggering antigen, thereby amplifying the immune response against that specific threat.
What are the main functions of antibodies once they are secreted into the body fluids?
Antibodies can neutralise pathogens by blocking their ability to bind to host cells, opsonise pathogens to enhance their phagocytosis by macrophages and other phagocytes, and activate the complement system, a cascade of proteins that can directly kill pathogens or enhance other immune mechanisms.
Define ‘epitope’.
An epitope is a specific region or structural feature on an antigen that is recognized by an antibody. Large antigens can have multiple epitopes, each potentially recognized by a different antibody.
Explain what is meant by antibody affinity, and how it can vary.
Antibody affinity refers to the strength of binding between an antibody and its specific epitope. Different antibodies can have varying affinities for the same antigen, influenced by factors like shape complementarity, charge interactions and hydrophobic interactions. Higher affinity generally translates to more effective neutralisation or opsonisation of the antigen.
How do polysaccharides differ from proteins in terms of their epitopes, and what implications does this have for antibody binding?
Polysaccharides often have repetitive epitopes, meaning the same structural feature is present in multiple copies. This allows for multiple identical antibodies to bind to the polysaccharide, creating a dense coating of antibodies. Proteins, in contrast, typically have more diverse epitopes, with different antibodies binding to distinct regions.
Explain the concept of immunological memory and its importance in protecting against subsequent infections.
Immunological memory results from the generation of long-lived memory B cells and T cells during the initial immune response. If the same antigen is encountered again, these memory cells enable a much faster and stronger secondary response, often preventing or significantly reducing the severity of disease. This is the basis of vaccination, where exposure to a harmless form of an antigen primes the immune system to respond effectively to the actual pathogen in the future.
Briefly describe the structure of a typical antibody molecule.
Antibodies, or immunoglobulins, typically have a Y-shaped structure composed of four polypeptide chains: two identical heavy chains and two identical light chains. The tips of the “Y” arms form the variable regions, responsible for antigen binding, while the stem of the “Y” constitutes the constant region, involved in effector functions like complement activation.
