Adaptive immune system : B and T Cells Flashcards
What are the two main components involved in adaptive immune responses?
Cellular and humoral components.
What are the three stages of the adaptive immune response?
Recognition of antigen
Activation of lymphocytes (B and T cells)
Attack against antigen and creation of memory.
Which cells are activated during the adaptive immune response?
B and T cells (lymphocytes).
What is the significance of the attack against the antigen in the adaptive immune response?
It leads to the destruction of the antigen and the creation of immune memory.
How is vaccination related to the adaptive immune response?
Vaccination leverages the stages of the adaptive immune response to create memory, offering protection against future infections.
What are two key features of adaptive immune responses?
Specificity and diversity.
What is the importance of memory in adaptive immune responses?
Memory allows the immune system to respond faster and more effectively upon subsequent exposure to the same antigen.
What is clonal expansion in the adaptive immune response?
The process where specific lymphocytes rapidly multiply after recognizing an antigen, increasing the number of cells that can fight the infection.
What does specialisation refer to in adaptive immunity?
It refers to the immune system’s ability to tailor responses to specific types of pathogens (viruses, bacteria, etc.).
What happens during contraction and homeostasis in the immune response?
After an infection is cleared, most activated immune cells die off, returning the system to a stable state.
What is non-reactivity to self in adaptive immunity?
It’s the ability of the immune system to distinguish between self and non-self, preventing attacks on the body’s own cells (self-tolerance).
Where do B and T lymphocytes originate?
They develop in the bone marrow from a haematopoietic stem cell (HSC).
What is the common precursor to B and T cells?
Common lymphoid progenitors (CLPs).
Where are immature B cells found, and where do mature B cells go?
Immature B cells are found in the bone marrow, and mature B cells move to peripheral lymphoid organs.
Where do B cells and T cells differentiate?
B cells remain in the bone marrow, while T cells migrate to the thymus to mature.
What are the early stages of B cell maturation?
Hematopoietic Stem Cell (HSC)
Pro-B cell (early and late)
What happens to B cells during maturation in terms of markers?
New markers are added at each stage of B cell development on the surface of the cell.
Where are immature B cells located, and where do they mature?
Immature B cells are found in the bone marrow, and they mature in the periphery (lymphoid organs).
What significant genetic event occurs during B cell maturation?
Re-arrangements of immunoglobulin gene segments occur, leading to the creation of a unique B cell receptor (BCR) by the time the cell reaches the immature B cell stage.
What are the stages of B cell maturation after the Pro-B cell?
Large Pre-B cell
Small Pre-B cell
What is the B cell receptor (BCR)?
The BCR is an immunoglobulin (IgM molecule) found on the surface of an immature B cell.
What type of immunoglobulin is the BCR similar to?
The BCR is similar to a free antibody, specifically IgM.
Where is the BCR found on a B cell?
The BCR is found on the surface of an immature B cell in the bone marrow.
Why is each immature B cell’s BCR unique?
Each BCR is unique due to the rearrangement of immunoglobulin gene segments during B cell development
Where are B cells generated and selected?
In the bone marrow.
What receptor do B cells express?
B cells express a B cell receptor (BCR) that recognizes antigens.
Are all B cell receptors (BCRs) the same?
No, each BCR is different and unique to each B cell.
How are BCRs generated?
Through recombination of genes, a process similar to how T cell receptors (TCRs) are generated.
What is another name for Immunoglobulin (Ig)?
Antibody.
How many polypeptides make up an immunoglobulin molecule?
Four interlinked polypeptides.
What are the two types of chains in an immunoglobulin molecule?
Two long heavy chains
Two short light chains
How many classes of immunoglobulins do mammals have?
Five classes: IgM, IgG, IgE, IgA, and IgD.
Which class of immunoglobulin is found in all vertebrates?
IgM.
Which two immunoglobulins are the most abundant in mammals?
IgM (pentamer) and IgG.
What is the primary role of IgM and IgG antibodies?
They provide the bulk of specific immunity against bacteria and viruses in extracellular fluid.
What is the role of IgE antibodies?
IgE participates in defenses against multicellular parasites and triggers allergic responses.
Where are IgA antibodies secreted, and what do they protect?
IgA (dimer) is secreted by plasma cells in the linings of the gastrointestinal, respiratory, and genitourinary tracts to provide local protection.
What is a major function of IgA in mammals?
It is the major antibody found in milk.
What is known about the function of IgD antibodies?
The function of IgD is unclear.
What part of the antibody binds to a specific antigen?
The variable region.
Do all antibodies recognize the same antigen?
No, different antibodies recognize and bind to different antigens or different parts of the same antigen.
What is the binding site of an antibody called?
The epitope.
What are the two types of epitopes antibodies can recognize?
Epitopes can be based on a linear sequence of the antigen or on its folding structure.
What are the main types of antigens?
Foreign antigens (heteroantigens)
Self-antigens (autoantigens)
Cancer cell-derived antigens (neoantigens)
What is the specific site on an antigen recognized and bound by an antibody called?
The epitope.
What is an antigen?
An antigen is a substance capable of stimulating an immune response.
What are examples of foreign antigens?
Microbes, proteins, large polysaccharides, complexed lipids, and nucleic acids.
What does the variable region of an antibody do?
The variable region varies among different B cells and specifically recognizes and binds to an antigen.
What is the constant region of an antibody also known as?
The Fc domain.
Are the constant regions identical for all antibodies of a given class?
Yes, the constant region (Fc domain) is identical for all antibodies within a specific class.
How is the B cell receptor (BCR) activated?
The BCR is activated by antigens and by cytokines from Helper T cells (T-dependent activation).
What are the three stages of adaptive immunity?
The humoral arm, carried out by B cells, is one of the three stages of adaptive immunity.
What is the role of specific antigen-binding sites on antibodies?
They allow antibodies to bind selectively to their corresponding antigens.
What happens to B cells upon activation?
Activated B cells proliferate into plasma cells that produce antibodies, and some differentiate into memory cells.
What is the primary role of B cells in humoral immunity?
They provide major defense against bacteria, viruses, other microbes in extracellular fluid, and against toxins.
What is the first stage of adaptive immune responses?
Recognition of antigen.
What happens in the third stage of adaptive immune responses?
Attack against the antigen and creation of memory.
What occurs in the second stage of adaptive immune responses?
Activation of lymphocytes (B and T cells).
What is the significance of memory in adaptive immune responses?
Memory allows for a faster and more effective immune response upon subsequent exposure to the same antigen.
What does each B lymphocyte possess for recognizing antigens?
Each B lymphocyte has a membrane receptor known as the B cell receptor (BCR).
What happens when an antigen binds to a lymphocyte receptor?
The antigen is “recognized” by the lymphocyte.
How specific is each lymphocyte in terms of antigen recognition?
Each lymphocyte is specific for just one type of antigen.
What happens to a lymphocyte upon binding to its specific antigen?
The lymphocyte undergoes cell division to make clones.
What are the two main functions of the clones produced from activated lymphocytes?
Plasma cells that carry out the attack on the antigen.
Memory cells for future encounters with the same antigen.
What role do plasma cells play in the immune response?
Plasma cells produce antibodies to attack the antigen.
What is the purpose of memory cells in the immune system?
Memory cells provide a faster and more effective response to future encounters with a particular antigen.
What is the process called when an antigen stimulates a lymphocyte to divide?
Clonal selection
What happens to an antigen-stimulated lymphocyte during T-dependent activation?
The lymphocyte divides and replicates itself.
What is true about the progeny of an activated lymphocyte?
All progeny express the same receptor as the original lymphocyte.
What do activated B cells differentiate into during the attack against antigens?
Activated B cells differentiate into plasma cells that secrete antibodies.
What role do activated cytotoxic T cells play in the immune response?
Activated cytotoxic T cells carry out the attack against infected or cancerous cells.
How long do plasma cells typically live after activation?
Plasma cells are short-lived.
What is the initial stage of B cell differentiation?
B cells begin as hematopoietic stem cells (HSC) in the bone marrow.
What happens to B cells during maturation in the bone marrow?
They undergo several stages, developing specific markers, and rearranging immunoglobulin genes to form unique B cell receptors (BCRs).
How are immature B cells characterised?
Immature B cells express B cell receptors (BCRs) and undergo selection processes to ensure functionality and self-tolerance.
What do plasma cells do?
Plasma cells secrete antibodies to target and neutralize specific antigens.
What occurs when an immature B cell successfully binds to an antigen?
It becomes activated, undergoes clonal expansion, and differentiates into plasma cells and memory cells.
What is one of the main functions of antibodies?
Neutralization of antigens.
What is the role of memory B cells?
Memory B cells persist in the body to provide a faster and more effective response upon re-exposure to the same antigen.
What system do antibodies help to activate?
The complement system.
How do antibodies assist in opsonization?
Antibodies coat bacteria, making them easier for phagocytes to recognize and engulf.
What is ADCC in the context of antibody function?
Antibody-dependent cellular cytotoxicity (ADCC) refers to the ability of antibodies to aid in killing infected or cancerous cells.
What is the role of B cells in the adaptive immune system?
B cells are part of the adaptive humoral immune system and produce antigen-specific immunoglobulins, typically known as antibodies.
What is the main function of T cells in the adaptive immune system?
T cells play a central role in adaptive immunity.
What are the two main types of immune responses mediated by T cells?
Cell-mediated immunity and help in activating B cells.
How do T cells assist B cells in the adaptive immune response?
Certain types of T cells, such as Helper T cells, provide signals and cytokines that activate B cells and enhance antibody production.
Where do T cells develop?
T cells develop in the bone marrow and mature in the thymus.
What is the purpose of T cell development?
The purpose is to generate a diverse collection of T cell receptors (TCRs).
What can be said about the types of T cells?
There are many different types of T cells, each with specific functions in the immune response.
Why is the diversity of T cell receptors important?
It allows the host to mount an adaptive immune response against a wide range of pathogens.
Where are T cells selected during their development?
T cells are selected in the thymus.
What happens to T cells after they mature in the thymus?
They migrate into the periphery.
How do T cells move through the body?
T cells circulate through lymph nodes.
What occurs when a T cell recognizes an antigen?
The T cell activates and acquires effector functions.
What does the adaptive immune system generate in terms of antigen specificity
A diverse range of antigen-specific cells.
What do the antigen-specific cells in the adaptive immune system recognize?
They recognize different antigens.
What is a potential issue with some of the antigen-specific cells generated?
Some of these cells may be specific for self-antigens.
What is the significance of clonal selection in the immune response?
Clonal selection ensures that only the lymphocytes that recognize and bind to a specific antigen are activated and proliferated.
Why is clonal deletion important in the immune system?
It prevents lymphocytes with self-reactive receptors from becoming problematic by recognizing self-antigens.
What happens to T cells that receive too little or too much of a signal during selection?
They are deleted through a process called apoptosis.
What is another mechanism, besides apoptosis, that helps regulate self-reactive T cells?
Inducing an inactive state called anergy.
What is the significance of inducing anergy in self-reactive lymphocytes?
Anergy prevents self-reactive lymphocytes from becoming activated and causing autoimmune responses.
What is one critical feature of lymphocyte development that distinguishes adaptive immunity?
Each lymphocyte expresses only one receptor specificity.
How is a lymphocyte’s DNA altered during development?
The lymphocyte’s DNA is irreversibly altered by gene rearrangement.
What are the two main types of protein chains that make up the T cell receptor (TCR)?
Often alpha (α) and beta (β) chains; sometimes gamma (γ) and delta (δ) chains.
What does the gene rearrangement during T cell development ensure?
It ensures that all progeny inherit the same receptor specificity.
What is the term used to describe the proliferation of an individual T cell into clones with identical antigen receptors?
Clonal expansion.
: What is the role of the variable regions in the TCR?
The variable regions recognize the diversity of antigens.
What is the structural characteristic of the TCR?
It is a transmembrane protein with a cytoplasmic tail.
What happens upon recognition of an antigen by the TCR?
Signaling occurs that activates the T cell.
How is the T cell receptor (TCR) generated?
The TCR is generated by random recombination and mutation of germline DNA for both TCR chains.
What is the significance of the random recombination and mutation in TCR generation?
It results in different TCRs for each T cell, allowing each T cell to recognize a different antigen.
Why is it important that each T cell recognizes a different antigen?
This diversity enables the immune system to respond to a wide range of pathogens.
What does the T cell receptor (TCR) generate?
A huge diversity of antigen-specific T cells.
Why might not all T cells generated be useful?
Some T cells may recognize self-antigens, leading to potential autoimmune responses.
What happens to T cells that do not recognize MHC (major histocompatibility complex)?
They are not activated and may undergo deletion during the selection process.
What is the purpose of T cell selection?
To ensure that only T cells that recognize foreign antigens presented by MHC molecules are allowed to mature and proliferate.
Where are T cells selected?
T cells are selected in the thymus.
What is tested during T cell selection in the thymus?
The T cell receptor (TCR) is tested to confirm that it functions properly and does not recognize self-antigens
How is the selection of T cells based on affinity?
T cells with strong affinity for self-antigens are deleted, while those with appropriate affinity for foreign antigens are retained.
What types of cells do useful T cells differentiate into?
They differentiate into either CD4+ ‘helper’ T cells or CD8+ ‘killer’ T cells.
What are the two main subsets of T cells?
CD4+ ‘helper’ T cells and CD8+ ‘killer’ T cells.
What is the role of CD4+ ‘helper’ T cells?
They assist other immune cells, including B cells and CD8+ T cells, in mounting an effective immune response
What percentage of αβ T cells are CD4 and CD8 subsets?
CD4 and CD8 subsets comprise the bulk of αβ T cells and are the main components of T-mediated immune responses.
What is the primary function of CD8+ ‘killer’ T cells?
They directly kill infected or cancerous cells.
Are there further subsets of T cells beyond CD4+ and CD8+?
Yes, there are further subsets of T cells derived from both CD4+ and CD8+ T cells.
What do T cells recognize in the immune response?
T cells recognize short peptides generated from pathogen-associated proteins.
How are these short peptides generated?
They are produced by phagocytes (innate cells) that digest pathogens.
What is the term used for the short peptides that T cells recognise?
Antigens.
Why is it important for T cells to recognize these short peptides?
Recognizing these peptides allows T cells to identify and respond to infected or abnormal cells.
How are peptides recognized by T cells?
Peptides are presented to the T cell receptor (TCR) in the context of Major Histocompatibility Complex (MHC).
What are the two forms of MHC?
MHC-I and MHC-II.
Which T cell subset interacts with MHC-II molecules?
CD4+ T cells.
Which T cell subset interacts with MHC-I molecules?
CD8+ T cells.
Where are MHC class I molecules expressed?
MHC class I molecules are expressed on all mammalian cells, including cells of epithelial origin.
Where are MHC class II molecules selectively expressed?
MHC class II molecules are selectively expressed on professional antigen-presenting cells, including dendritic cells, macrophages, and B cells.
How are antigens recognized when they are engulfed from outside the cell?
Antigens engulfed from outside the cell (e.g., bacteria) are presented via MHC II to CD4+ T cells.
How are antigens presented when they come from inside the cell?
Antigens presented from inside the cell (e.g., viruses) are displayed via MHC I to CD8+ T cells.
What determines how antigens are presented to T cells?
The right stimulus determines how antigens are presented to T cells.
Which type of cells are very effective at presenting antigens?
Dendritic cells are very good at presenting antigens via both MHC I and MHC II.
What do naïve antigen-specific T cells do?
They recirculate looking for phagocytes presenting their cognate antigen.
What occurs upon recognition of the antigen/MHC by a T cell?
The T cell and antigen-presenting cell form an interaction.
What role does the T cell receptor (TCR) play upon antigen recognition?
The TCR transmits signals that activate the T cell.
What is the outcome of T cell activation?
The activated T cell will proliferate and differentiate into effector cells that perform various immune functions.
Why is the proliferation of T cells necessary after activation?
The huge diversity of T cells means that antigen-specific T cells are rare, so they need to proliferate to generate an effective immune response.
What happens to activated T cells during proliferation?
Activated T cells proliferate rapidly and differentiate into functional effector T cells.
What are effector T cells responsible for?
Effector T cells carry out various immune functions, including killing infected cells and helping other immune cells.
How does the proliferation of T cells contribute to the immune response?
It increases the number of antigen-specific T cells, enhancing the body’s ability to fight off infections.
What are the effector functions of CD4+ T cells?
CD4+ T cells have a ‘helper’ function, assisting other immune cells in the immune response.
What is the primary function of CD8+ T cells?
CD8+ T cells have a ‘killer’ function, directly killing infected or cancerous cells.
What factors determine whether T-helper cells differentiate into Th1 or Th2 cells?
The type of cytokines present during activation and the nature of the antigen (e.g., intracellular vs. extracellular pathogens) influence whether T-helper cells become Th1 or Th2.
What is the function of Th1 cells in the immune response?
Th1 cells secrete IFN-γ and activate macrophage functions.
What is the role of Th1 cells?
Th1 cells primarily help activate macrophages and are important for the immune response against intracellular pathogens.
What is the role of Th2 cells?
Th2 cells assist in activating B cells and are important for the immune response against extracellular pathogens, particularly in allergic responses.
How do Th1 and Th2 cells differ in their immune functions?
Th1 cells are involved in activating macrophages for intracellular pathogen defense, while Th2 cells focus on aiding antibody production against extracellular pathogens
What happens to the number of T cells specific for an antigen after an infection?
The number of T cells specific for the antigen increases dramatically and then drops off.
What cytokine is primarily secreted by Th2 cells?
Th2 cells secrete IL-4.
What role do Th2 cells play in the immune response?
Th2 cells help promote antibody production by B cells.
What is left after the initial increase in T cells post-infection?
A low level of memory T cells remains.
Why is the presence of memory T cells significant?
Memory T cells are a key feature of the ‘adaptive’ immune system, allowing for a quicker and more effective response upon re-exposure to the same antigen.
How does the adaptive immune system differ from the innate immune system in terms of memory?
The adaptive immune system has memory T cells that provide long-lasting immunity, whereas the innate immune system does not have this memory capability.
Do memory T cells need additional signals for proliferation?
yes, memory T cells still require the correct signals to allow proliferation.
What is required for the survival of memory T cells?
Memory T cells require sustained stimulation by IL-7 and IL-5 for survival.
What role do vaccines play in T cell memory?
Vaccines stimulate the adaptive immune system to produce memory T cells against specific pathogens without causing the disease.
What is the role of IL-7 in memory T cell maintenance?
IL-7 promotes the survival of memory T cells by providing essential survival signals.
What is the role of IL-5 in memory T cell functions?
IL-5 aids in the growth and differentiation of memory T cells, enhancing their response capabilities.
What is a potential issue with recognizing self-antigens in the adaptive immune system?
Not all antigens are harmful; self-antigens can lead to autoimmunity if misrecognized.
Why is cross-talk important between the innate and adaptive immune systems?
Cross-talk helps control immune responses, preventing harmful reactions to non-harmful antigens.
What are “danger” signals?
Danger signals are alarm signals from injured or stressed cells that alert the immune system to potential threats
What does the random generation of specificity in adaptive immunity allow?
It allows the lymphocyte population to recognize antigenic peptides from many potential pathogens.
What is a disadvantage of the random specificity in adaptive immunity?
It can lead to autoimmunity, allergies, and food sensitivities if the immune system mistakenly targets non-harmful substances.
How does adaptive immunity help prevent pathogen evasion?
It allows for the recognition and targeting of diverse antigenic peptides, stopping pathogens from evading the immune system.
What activates the immune system?
The immune system is activated by inflammatory inducers that indicate the presence of pathogens or tissue damage.
How quickly does innate immunity respond to threats?
Innate immunity is normally initiated within minutes, with the initial response observable within hours.
How does the timeline of the adaptive immune response differ from innate immunity?
The adaptive immune response takes over later, with a variable timeline that can span days to weeks, and even years if the infection persists.
What is a critical aspect of the adaptive immune response?
The critical induction of memory, including the production and maintenance of memory T cells, is a key aspect of the adaptive immune response.
What role do memory T cells play in the immune response?
Memory T cells enable a quicker and more robust response to previously encountered pathogens upon re-exposure.
