Mast Cells, Dendritic Cells & NK Cells

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Questions and Answers

Considering the maturation process and location of mast cells, how might their strategic placement in the skin, intestines, and airway mucosa contribute to their protective function?

Their strategic placement allows them to act as sentinels, ready to release inflammatory mediators at the first sign of tissue invasion by pathogens.

How does the functional shift of dendritic cells from phagocytic activity to T lymphocyte activation represent a critical link between innate and adaptive immunity?

The shift signifies the transition from direct pathogen elimination to initiating a targeted, long-term immune response by presenting processed antigens to T cells.

Explain how the mechanism by which NK cells recognize and destroy target cells differs fundamentally from that of T lymphocytes, and why this difference is crucial for innate immunity?

NK cells use Fc receptors to detect antibody-coated cells, providing a broad, immediate response, whereas T cells require specific antigen recognition, enabling a tailored but delayed response. This difference insures there is an immediate immune response.

If a patient has a genetic defect that impairs the migration of mast cell precursors from the bone marrow to peripheral tissues, what broad categories of immune challenges would they likely be more susceptible to, and why?

They would be more susceptible to parasitic infections and allergic reactions due to the reduced presence of mast cells to initiate inflammatory responses in tissues exposed to external pathogens and allergens. Signup and view all the answers

Considering that NK cells can recognize antibody-coated cells, how might a deficiency in antibody production impact the effectiveness of NK cell-mediated cytotoxicity, and what other immune cells or mechanisms could potentially compensate for this deficiency?

A deficiency would impair NK cell activation, reducing their ability to eliminate infected or cancerous cells. Macrophages and complement-mediated lysis could compensate, though less effectively. Signup and view all the answers

How does the macropinocytosis process in dendritic cells (DCs) contribute to the initiation of adaptive immune responses?

Macropinocytosis enables DCs to non-discriminately sample a wide range of extracellular material, increasing the probability of capturing relevant antigens. The captured antigens are then processed and presented to T cells in the lymph nodes, initiating an adaptive immune response. Signup and view all the answers

Describe the molecular mechanisms and cellular interactions that allow T lymphocytes to efficiently patrol and survey lymph nodes for their cognate antigens, referencing the key steps in their recirculation between blood and lymph nodes.

T lymphocytes enter lymph nodes from the blood via high endothelial venules (HEVs), guided by chemokines like CCL21. If they don't encounter their cognate antigen, they exit via efferent lymphatic vessels, re-entering the blood through the thoracic duct. This constant recirculation, driven by chemokine gradients and adhesion molecules, maximizes their chances of finding a specific antigen. Signup and view all the answers

Detail the sequence of events that follows after a T cell recognizes its cognate antigen on a dendritic cell (DC), explaining how this interaction leads to both clonal expansion and the differentiation into effector and memory cells.

Upon recognizing its cognate antigen on a DC, the T cell receives co-stimulatory signals, activating intracellular signaling pathways that induce the expression of genes promoting proliferation and differentiation. Clonal expansion generates a large population of T cells specific for the antigen, while differentiation leads to effector cells for immediate response and memory cells for long-term immunity. Signup and view all the answers

Explain how the migration of dendritic cells (DCs) from peripheral tissues to draining lymph nodes integrates innate and adaptive immunity, detailing the signals and processes involved in antigen uptake, DC activation, and subsequent T cell activation.

In peripheral tissues, DCs capture antigens and undergo activation, upregulating co-stimulatory molecules and chemokine receptors. They then migrate to draining lymph nodes, guided by chemokines, where they present processed antigens to T cells. This process links the innate detection of antigens in the periphery to the adaptive immune response in the lymph nodes. Signup and view all the answers

Describe how the temporal dynamics of antigen presentation by dendritic cells (DCs) influence the balance between T cell tolerance and immunity, considering factors such as antigen dose, co-stimulatory signals, and the presence of inflammatory cytokines.

High antigen dose in the absence of co-stimulation or inflammatory signals can induce T cell tolerance, while optimal antigen dose with strong co-stimulation and inflammatory cytokines promotes T cell activation and immunity. The duration and context of antigen presentation by DCs thus determine the fate of T cell responses, influencing whether tolerance or immunity prevails. Signup and view all the answers

Beyond LPS and lipoteichoic acids, describe two hypothetical molecular structures that could differentiate host cells from pathogens and thus function as PAMPs.

Pathogen-specific nucleic acids, such as dsRNA or unmethylated CpG DNA, are absent in host cells and can be recognized by PRRs. Unique surface glycoproteins or glycolipids found only on pathogens' cell membranes can also serve as PAMPs. Signup and view all the answers

If a patient's macrophages failed to express functional TLR-4, how would their initial immune response to a Gram-negative bacterial infection be affected?

The initial inflammatory response would be significantly impaired. Macrophages would not effectively recognize LPS, leading to reduced production of inflammatory mediators and delayed recruitment of other immune cells to the site of infection. Signup and view all the answers

Explain how vasodilation and edema, while beneficial for initial immune response, can potentially contribute to pathological outcomes if left unchecked?

Excessive vasodilation can lead to a dangerous drop in overall blood pressure. Uncontrolled edema can impair organ function by restricting blood flow and oxygen delivery, eventually leading to tissue damage. Signup and view all the answers

How could the adaptive immune system be affected if a person had a genetic defect that impaired the ability of antigen-presenting cells (APCs) to migrate to lymph nodes?

The activation of T cells would be significantly impaired. Without APC migration, T cells wouldn't be able to efficiently encounter and recognize foreign antigens, compromising the development of adaptive T cell responses. Signup and view all the answers

Considering the roles of both T cells and B cells in adaptive immunity, how may a deficiency in T cell function impact the ability of B cells to produce high-affinity, class-switched antibodies?

T cell deficiency impairs B cell activation through the lack of cytokine stimulation, leading to a reduced ability for B cells to undergo affinity maturation and class switching. This results in lower-affinity, short-lived antibody responses. Signup and view all the answers

In what ways would the immune response to a viral infection differ in a patient who is unable to produce antibodies compared to one who is unable to activate cytotoxic T lymphocytes (CTLs)?

Without antibodies, the virus can spread unimpeded through the body and infect more cells. Without CTLs, the body cannot directly eliminate the virally infected cells, meaning viruses can continue to replicate within those cells. Signup and view all the answers

In the context of tissue transplantation, explain why understanding the principles of both innate and adaptive immunity is crucial for preventing graft rejection.

The innate immune response can initiate inflammation and activate APCs, leading to T cell-mediated rejection. Adaptive immunity then allows for specific recognition and destruction of the graft by T cells and antibodies. Preventing both arms of the immune system from targeting the graft is often necessary for long-term acceptance. Signup and view all the answers

How might chronic exposure to low levels of a specific PAMP, such as a component of the gut microbiome that leaks into circulation, influence the development of autoimmune disorders?

Chronic PAMP exposure can lead to persistent immune activation, causing dysregulation of immune tolerance mechanisms and increasing the risk of autoreactive lymphocyte activation. This can result in the immune system attacking the individual's own tissues, leading to autoimmune disorders. Signup and view all the answers

Explain how the theoretical diversity of T cell receptors (TCRs) addresses the challenge of recognizing a vast number of pathogens and pathogen-derived antigens.

The immense theoretical diversity of TCRs (estimated at 2 x 10^18 sequences) ensures that the adaptive immune system can potentially recognize and respond to virtually any foreign antigen, as there is likely a TCR that can bind to any given antigen. Signup and view all the answers

Describe the key differences between a naïve lymphocyte and an effector lymphocyte in terms of antigen exposure and function.

A naïve lymphocyte has not yet encountered its cognate antigen, while an effector lymphocyte has been activated by antigen recognition and has acquired specific effector functions such as killing infected cells or activating other leukocytes. Signup and view all the answers

Explain the importance of clonal expansion in adaptive immunity, particularly in the context of generating an effective immune response against a pathogen.

Clonal expansion generates a large population (millions!) of antigen-specific T cells, which is essential for effectively combating a pathogen. Without clonal expansion, there would not be enough T cells bearing the right receptor to clear the infection. Signup and view all the answers

Outline the steps a naive lymphocyte undergoes when it encounters a foreign antigen presented by an antigen-presenting cell, ultimately leading to an effective immune response.

The naïve lymphocyte is activated upon recognizing its cognate antigen on an antigen-presenting cell. It then undergoes proliferation and differentiation, giving rise to a large number of antigen-specific effector cells that can clear the pathogen. Signup and view all the answers

How does clonal selection ensure that the adaptive immune response is specific to the invading pathogen and doesn't target self-antigens?

Clonal selection activates and expands only those lymphocytes with receptors specific to foreign antigens, while lymphocytes recognizing self-antigens are typically eliminated or inactivated, preventing autoimmunity. Signup and view all the answers

Contrast the effector functions of CD8+ T cells and CD4+ T cells in adaptive immunity. How do their roles complement each other in eliminating pathogens?

CD8+ T cells kill target infected cells directly, whereas CD4+ T cells help activate other leukocytes, such as B cells and macrophages, to enhance their immune functions. They complement each other by directly eliminating infected cells and coordinating the overall immune response. Signup and view all the answers

How does the concept of clonal selection address the challenge that 'fighting' a pathogen requires an army of antigen-specific T cells, given the limited initial number of naïve lymphocytes?

Clonal selection allows for the rapid amplification of rare, antigen-specific naïve lymphocytes into a large army of effector cells through proliferation and differentiation, overcoming the initial scarcity of antigen-specific cells. Signup and view all the answers

Considering a scenario where a naïve lymphocyte binds to an antigen but does not receive the necessary co-stimulatory signals. What is the likely outcome, and how does this prevent an unwanted immune response?

In the absence of co-stimulatory signals, the lymphocyte is likely to become anergic or undergo apoptosis, which prevents its activation and proliferation. This mechanism prevents unwanted immune responses against harmless antigens or self-antigens. Signup and view all the answers

Describe the critical role dendritic cells play in bridging innate and adaptive immunity, detailing the mechanisms by which they capture, process, and present antigens to T cells in secondary lymphoid tissues.

Dendritic cells (DCs) capture antigens through macropinocytosis, process them into peptides, migrate to draining lymph nodes, and present these peptides on MHC molecules to T cells, initiating adaptive immune responses. Signup and view all the answers

Explain the concept of clonal selection in adaptive immunity, including how the recognition of a foreign antigen leads to the proliferation and differentiation of naïve lymphocytes into effector cells.

Clonal selection involves the activation of naïve lymphocytes upon recognizing a specific antigen, leading to their proliferation and differentiation into effector cells, creating a large population of antigen-specific cells. Signup and view all the answers

Distinguish between the effector functions of CD8+ and CD4+ T cells in adaptive immunity, detailing how each type of T cell contributes to the elimination of pathogens during an infection.

CD8+ T cells directly kill infected target cells, while CD4+ T cells help activate other leukocytes, such as B cells and macrophages, to enhance the immune response against pathogens. Signup and view all the answers

Describe the roles of antibodies in adaptive immunity, include how their specific binding to foreign antigens inactivates pathogens and facilitates their clearance.

Antibodies bind specifically to foreign antigens, neutralizing pathogens by blocking their ability to infect cells. They also mark pathogens for destruction by phagocytes or complement activation, leading to their clearance. Signup and view all the answers

Explain how vaccination leverages the principles of adaptive immunity to protect against future infections.

Vaccination introduces a harmless form of a pathogen, triggering an adaptive immune response that results in the creation of memory lymphocytes and antibodies, providing long-term protection against future infections by the same pathogen. Signup and view all the answers

How do transmembrane antibodies differ from secreted antibodies in terms of function and location within the immune system?

Transmembrane antibodies (membrane-bound antibodies) function as B cell receptors, recognizing antigens and initiating B cell activation. Secreted antibodies are released by plasma cells to neutralize pathogens and mediate effector functions throughout the body. Signup and view all the answers

Discuss the cooperation between T cells (both CD4+ and CD8+) and B cells in a typical adaptive immune response against a viral infection. How do these cells interact to eliminate the virus?

CD8+ T cells kill virus-infected cells, while CD4+ T cells activate B cells to produce antibodies that neutralize the virus and mark infected cells for destruction. This coordinated response ensures efficient viral clearance and long-term immunity. Signup and view all the answers

Explain how the adaptive immune response, while highly specific and effective, can sometimes lead to immunopathology. Provide an example of a situation where the adaptive immune response causes harm to the host.

In autoimmune diseases, the adaptive immune system mistakenly targets self-antigens, leading to chronic inflammation and tissue damage, such as in rheumatoid arthritis where antibodies attack joint tissues. Signup and view all the answers

How does the absence of afferent lymphatics in Peyer's patches influence the initiation of the adaptive immune response in the gut?

The absence of afferent lymphatics means that antigen enters directly from the gut lumen via M cells, rather than being filtered through lymph nodes first. This allows for immediate sampling of gut contents. Signup and view all the answers

In the context of splenic function, how do macrophages in the red pulp contribute to immune homeostasis and prevent systemic complications?

Red pulp macrophages phagocytose old or damaged red blood cells and immune complexes, preventing their accumulation and potential inflammatory responses. Signup and view all the answers

Contrast the roles of follicular dendritic cells (FDCs) and dendritic cells (DCs) in initiating and shaping the adaptive immune response within secondary lymphoid organs.

DCs present processed antigens to T cells in the T cell zone, initiating T cell activation. FDCs, found in B cell follicles, display intact antigens to B cells, crucial for B cell activation and affinity maturation. Signup and view all the answers

Describe the functional significance of the periarteriolar lymphoid sheath (PALS) in the spleen, particularly in the context of T cell activation.

The PALS is the T cell zone of the spleen's white pulp, enriched in DCs, facilitating the crucial interactions between DCs presenting antigens and T cells, initiating T cell activation and adaptive immunity. Signup and view all the answers

How do the distinct anatomical structures of B cell follicles and T cell zones within secondary lymphoid organs contribute to the development of a coordinated adaptive immune response?

Spatial segregation allows for specialized microenvironments: T cell zones for T cell priming by DCs, and B cell follicles for B cell activation, proliferation, and affinity maturation, enabling coordinated humoral and cellular responses. Signup and view all the answers

What mechanisms regulate neutrophil trafficking from the bone marrow to sites of infection, and how does this process contribute to acute inflammation?

Chemokines (e.g., IL-8) released at infection sites signal to neutrophils, promoting their release from bone marrow and migration through blood vessels into inflamed tissues. Signup and view all the answers

Considering the relatively short lifespan of neutrophils, what aspects of their function make them critical in the context of acute infections, and what are the potential consequences of their dysregulation?

Neutrophils are rapidly recruited and efficiently phagocytose and kill pathogens; dysregulation can lead to excessive inflammation and tissue damage due to release of toxic granule contents. Signup and view all the answers

How do eosinophils and basophils contribute to both protective immunity against parasitic infections and the pathogenesis of allergic diseases?

In parasitic infections, they release toxic granules to kill parasites; in allergies, they are activated by IgE, releasing mediators that cause inflammation and tissue damage. Signup and view all the answers

Flashcards

Adaptive Immunity Initiation

Adaptive immune responses start when antigen and antigen-presenting cells meet in secondary lymphoid tissues.

Dendritic Cells (DCs)

Dendritic cells are major antigen-presenting cells that capture and present antigens to T cells.