Innate & Adaptive Immunity Flashcards
explain the innate immune system and the adaptive immune system
Innate Immune System:
The innate immune system is the first line of defense against pathogens. It provides rapid, non-specific protection.
Components of the innate immune system include physical barriers (e.g., skin and mucous membranes), phagocytic cells (e.g., neutrophils and macrophages), natural killer (NK) cells, and complement proteins.
These components work together to detect and eliminate pathogens without prior exposure or memory of the specific invader.
Adaptive Immune System:
The adaptive immune system is a more specialized and targeted defense mechanism.
It involves immune cells known as lymphocytes, which include B cells and T cells. B cells are responsible for antibody production, while T cells have various roles, such as cytotoxic T cells that kill infected cells.
The adaptive immune system has memory, meaning it can “remember” specific pathogens, allowing for a faster and more effective response upon subsequent exposure.
Molecular Components:
Specialized molecules play a crucial role in immune responses. These include cytokines (signaling molecules that regulate immune cell communication), antibodies (produced by B cells to neutralize pathogens), and complement proteins (a set of proteins that enhance immune responses).
Cellular Components:
Immune cells, such as lymphocytes, macrophages, and dendritic cells, play vital roles in detecting, capturing, and destroying pathogens. They migrate to sites of infection or inflammation.
Organs:
Various organs in the body are involved in immune function, including the thymus (site of T cell maturation), spleen (filters blood and removes damaged blood cells), and lymph nodes (where immune cells interact and mount immune responses).
Adhesion Proteins:
Adhesion proteins are molecules that help immune cells attach to target cells or tissues, facilitating their movement to the site of infection or inflammation.
explain the innate immune system’s major components
The innate immune system is the body’s first line of defense against invading pathogens and provides an immediate response to protect the host. This system primarily consists of two major components:
Phagocytic Cells: The innate immune system includes various types of phagocytic cells, such as monocytes, macrophages, and polymorphonuclear leukocytes. The polymorphonuclear leukocytes further include neutrophils, eosinophils, and basophils. These cells play a crucial role in attacking and eliminating invading microorganisms.
Mechanism: Phagocytic cells use their cell membrane to engulf pathogens, such as bacteria, viruses, or other harmful agents. Once internalized, the pathogen is enclosed within an internal compartment called a phagosome.
Lysosome Fusion: Phagosomes then fuse with lysosomes present in the cell’s cytoplasm. Lysosomes contain hydrolytic enzymes and reactive oxygen species, which have a powerful antimicrobial effect. These enzymes and reactive oxygen species work together to break down and digest the internalized pathogen, ultimately destroying it.
Dendritic Cells: Dendritic cells are another important component of the innate immune system. They serve as antigen-presenting cells and are essential for initiating adaptive immune responses. Dendritic cells capture antigens from pathogens and present them to T cells, which then trigger specific immune responses.
The innate immune system’s rapid response is critical in providing immediate protection against infections. It acts as a first line of defense to prevent pathogens from causing extensive damage while also facilitating the activation of adaptive immunity for more specific and long-lasting protection.
explain phagocytes
Phagocytes: Phagocytes are a group of white blood cells that have the ability to engulf and digest invading microorganisms. They are essential for the body’s defense against infections. The main types of phagocytes include neutrophils, monocytes, and macrophages.
Macrophages: Macrophages are a type of phagocytic cell. They have several important functions in the immune system. Unlike some other immune cells, macrophages can leave the circulatory system by squeezing through the walls of capillary blood vessels and migrate to tissues where they are needed. Once they reach an area with pathogens, they can efficiently engulf and destroy the invading microorganisms. Macrophages also play a key role in immune regulation by releasing signaling molecules called cytokines. These cytokines help recruit and activate other immune cells to join the fight against infections.
explain the crucial components of the innate immune system
Neutrophils: Neutrophils are a type of white blood cell, and they are part of the body’s first line of defense against infections. Neutrophils contain granules in their cytoplasm that are filled with toxic substances. When they encounter bacteria or fungi, they release these toxins to kill or inhibit the growth of the invading microorganisms.
Natural Killer (NK) Cells: Natural Killer cells are a type of lymphocyte, a white blood cell. They play a crucial role in immune surveillance. NK cells are able to recognize and destroy infected host cells, such as cells infected with viruses or cancerous cells. By eliminating these infected cells, NK cells help stop the spread of infections.
Dendritic Cells: Dendritic cells are specialized immune cells with the unique ability to capture, process, and present antigens. Antigens are substances that trigger an immune response when they enter the body. Dendritic cells act as messengers for the immune system. When they encounter an antigen (e.g., a piece of a virus), they “present” it to other immune cells, such as T cells and B cells. This presentation helps activate these cells and directs the adaptive immune response against the specific antigen.
These components work together to provide an immediate and non-specific defense against infections. Neutrophils act to directly kill invading microorganisms. NK cells target infected host cells, and dendritic cells play a key role in alerting the adaptive immune system to specific threats.
explain phagocytosis
Chemotaxis: When the body is under attack by pathogens, various immune responses are initiated. One of the initial responses is the release of chemicals, including histamine, which can attract immune cells like neutrophils to the site of infection. The movement of immune cells toward a chemical stimulus is called chemotaxis.
Recognition: Neutrophils, in particular, have receptor proteins on their surfaces that can recognize and attach to molecules like antibodies. Antibodies are produced by the immune system and can specifically target pathogens. When neutrophils encounter pathogens that are marked with antibodies, they attach to the pathogen’s surface.
Engulfment: Once attached to the pathogen, the neutrophil’s cell membrane surrounds the pathogen and engulfs it. This process is called endocytosis, and it forms a phagocytic vacuole, also known as a phagosome, around the pathogen.
Fusion with Lysosomes: The phagosome, containing the engulfed pathogen, fuses with lysosomes. Lysosomes are cellular organelles filled with hydrolytic enzymes and reactive oxygen species.
Destruction: Once the phagosome fuses with the lysosome, the contents of the lysosome are released into the phagosome. The hydrolytic enzymes and reactive oxygen species in the lysosome act to digest and destroy the internalized pathogen. This destruction process is essential for eliminating the invading microorganism.
explain dendritic cells
Origin and Distribution: Dendritic cells are derived from bone marrow and share a lineage with monocytes. They exist in the body’s tissues as “immature” dendritic cells.
Microbial Capture: Immature dendritic cells located within the body’s tissues serve as the first line of defense against invading microbes. When these dendritic cells encounter microbes, they can capture and internalize them. This internalization activates the dendritic cells.
Activation and Maturation: Upon capturing microbes, dendritic cells become activated. Activated dendritic cells then undergo maturation, a process that equips them to carry out their role more effectively.
Transport to Lymph Nodes: Maturation prepares dendritic cells to migrate to the lymphatic system. They travel to the lymph nodes, which are important sites for immune response coordination.
Antigen Presentation: In the lymph nodes, mature dendritic cells present the microbial antigens they’ve captured to the adaptive immune system. This presentation is a critical step in the initiation of an adaptive immune response.
Cytokine and Chemokine Secretion: Dendritic cells are not just antigen-presenting cells. They also secrete various signaling molecules such as interferon-alpha (IFN-alpha), interleukin-12 (IL-12), and chemokines. These molecules play a role in regulating immune responses. For example, they can induce the differentiation of lymphocytes and promote an inflammatory response.
The ability of dendritic cells to capture and present antigens from pathogens to the adaptive immune system makes them essential for the initiation of specific and targeted immune responses. They act as a bridge between innate immunity and adaptive immunity, helping the body combat infections effectively.
explain how the recognition of foreign substances is a crucial aspect of the immune response
Danger Signals: The innate and adaptive immune systems are both activated when they detect “danger signals” associated with foreign organisms. These danger signals serve as indicators of potential threats to the body.
Pathogen-Associated Molecular Patterns (PAMPs): These danger signals often include specific molecular motifs called Pathogen-Associated Molecular Patterns (PAMPs). PAMPs are common, conserved structural elements found on the surface of many pathogens, such as bacteria, viruses, and fungi. These patterns are shared among different strains of pathogens and are not found in the host’s own cells.
Recognition by Pattern Recognition Receptors (PRRs): The innate immune system primarily relies on non-antigen-specific receptors known as Pattern Recognition Receptors (PRRs). These receptors are present on cells like dendritic cells and phagocytes. PRRs are responsible for recognizing and binding to PAMPs when they encounter them.
Initiation of Immune Response: When PRRs on immune cells bind to PAMPs, it triggers an immune response. The activation of PRRs sends signals within the immune system, alerting it to the presence of a potential threat.
This early recognition process is part of innate immunity, providing a rapid and generalized response to pathogens. The immune system’s ability to identify these common molecular patterns allows it to quickly identify and respond to a wide range of pathogens, even those it has never encountered before.
The adaptive immune system, on the other hand, relies on antigen-specific receptors, such as B cell receptors and T cell receptors, to recognize and target specific antigens associated with pathogens. This specificity allows the adaptive immune system to develop a tailored response to the particular pathogen it encounters.
explain Pattern Recognition Receptors (PRRs)
Pattern Recognition Receptors (PRRs) play a critical role in recognizing Pathogen-Associated Molecular Patterns (PAMPs) and initiating immune responses. Here’s more information on PRRs and some examples of them:
Toll-like Receptors (TLRs): TLRs are a family of PRRs that recognize various PAMPs, such as pathogen RNA, DNA, lipopolysaccharides, and other microbial components. Different TLRs are specific for different PAMPs.
Chemotactic Receptors: These receptors are involved in chemotaxis, which is the directed movement of immune cells toward the source of a chemical signal. This helps immune cells locate and respond to sites of infection or inflammation.
Phagocytic Receptors: These receptors are expressed on phagocytic cells like macrophages and neutrophils. They play a role in the recognition and uptake of pathogens for subsequent destruction.
Mannan Binding Lectin (MBL): MBL is involved in the recognition of sugar motifs present on the surface of pathogens. It can initiate the complement pathway to enhance the immune response.
DC1: This is likely a reference to dendritic cell receptors, which can interact with lipids on pathogens. Dendritic cells are key players in presenting antigens to the adaptive immune system.
When PRRs on immune cells engage with their corresponding PAMPs, it triggers a cascade of events that lead to the internalization and removal of the pathogen. This process is crucial for the early defense against infections and the activation of immune responses.
Each PRR has its own specificities, and collectively, they allow the immune system to recognize a wide range of pathogens based on the unique molecular patterns present on these invaders. This innate recognition is a fundamental aspect of immune surveillance and defense.
explain the adaptive immune system
B Lymphocytes (B Cells): These immune cells are responsible for the humoral immune response. B cells can produce antibodies, also known as immunoglobulins (Ig). These antibodies can recognize and bind to specific antigens (foreign substances), marking them for destruction. B cells play a central role in fighting infections by preventing pathogens from entering host cells.
T Lymphocytes (T Cells): T cells are involved in cellular immune responses. There are different types of T cells with specific functions:
Helper T Cells (CD4+ T Cells): These cells play a central role in coordinating immune responses. They help activate other immune cells, such as B cells and cytotoxic T cells, to fight infections. Helper T cells are involved in both humoral and cellular immunity.
Cytotoxic T Cells (CD8+ T Cells): These T cells are responsible for directly killing infected host cells. They recognize and destroy cells infected with viruses or other intracellular pathogens.
Regulatory T Cells (Tregs): These cells are involved in suppressing immune responses. They help maintain immune tolerance to prevent the immune system from attacking healthy cells and tissues. Tregs are crucial for preventing autoimmune reactions.
The adaptive immune system relies on the recognition of specific antigens, and it generates highly targeted responses against these antigens. Memory B and T cells are also formed during adaptive immune responses, providing long-term immunity against previously encountered pathogens.
explain how the adaptive immune system relies on the recognition of pathogens through antigen-specific receptors on B and T lymphocytes
Antigen-Specific Receptors:
B Cells: B cells possess immunoglobulin receptors, also known as B cell receptors (BCRs). BCRs are membrane-bound antibodies that can specifically recognize and bind to antigens. Each B cell expresses a unique BCR, leading to a vast diversity of receptor specificities.
T Cells: T cells have T-cell receptors (TCRs) on their surfaces. TCRs can recognize specific antigens when they are presented by antigen-presenting cells (APCs), such as dendritic cells or macrophages. TCRs are highly diverse and play a crucial role in T cell activation.
Antigen Recognition:
Antigen recognition by B cells occurs when the BCR on a B cell’s surface binds to an antigen. This binding activates the B cell and initiates the humoral immune response. B cells can produce antibodies (also known as immunoglobulins) that specifically target the recognized antigen.
Antigen recognition by T cells is slightly different. T cells do not directly recognize free-floating antigens but require antigen presentation. APCs process antigens from pathogens and present them on their surfaces along with major histocompatibility complex (MHC) molecules. TCRs on T cells can recognize these antigen-MHC complexes. There are two main classes of MHC molecules: MHC class I (presenting intracellular antigens) and MHC class II (presenting extracellular antigens).
Secondary Lymphoid Organs:
Lymphocytes constantly patrol the body for pathogens, but the process of antigen recognition and immune response initiation typically occurs in secondary lymphoid organs. These organs serve as sites for lymphocyte activation, proliferation, and interaction with APCs. Common secondary lymphoid organs include the spleen, lymph nodes, tonsils, and Peyer’s patches.
explain the cellular immune response, particularly the activation of T cells
T Cell Activation by Antigen Presentation:
T cells, specifically CD4+ helper T cells and CD8+ cytotoxic T cells, require the presentation of pathogenic antigens to become activated.
Antigen presentation is a process where host cells display fragments of antigens derived from pathogens on their cell surfaces for recognition by T cells.
Major Histocompatibility Complex (MHC) Molecules:
MHC molecules are cell surface receptors that serve as the “presentation platforms” for antigens. These molecules are crucial for antigen recognition by T cells.
There are two main classes of MHC molecules: MHC class I and MHC class II.
MHC Class I:
MHC class I molecules are expressed on the surfaces of most nucleated cells in the body.
They present antigens derived from intracellular pathogens, such as viruses or intracellular bacteria.
CD8+ cytotoxic T cells recognize antigen-MHC class I complexes. Once recognized, they become activated to destroy infected host cells.
MHC Class II:
MHC class II molecules are mainly expressed on the surfaces of professional antigen-presenting cells (APCs), such as dendritic cells, macrophages, and B cells.
They present antigens derived from extracellular pathogens, like bacteria or fungi.
CD4+ helper T cells recognize antigen-MHC class II complexes. Upon recognition, they become activated and play a central role in coordinating various immune responses, including the activation of B cells, cytotoxic T cells, and other immune effectors.
Antigen Recognition and Immune Response:
Antigen-presenting cells (APCs) capture pathogens, process them, and display antigen fragments on their surfaces bound to MHC molecules.
When T cells encounter these antigen-MHC complexes that match their specific T cell receptors (TCRs), they become activated.
Activated T cells then initiate various immune responses, including the activation of B cells (helper T cells), killing of infected host cells (cytotoxic T cells), or the release of
inflammatory signals to recruit and activate other immune cells. The coordination of these responses is essential for an effective immune reaction against the invading pathogens. Additionally, the activation of T cells leads to clonal expansion, generating a population of effector T cells capable of recognizing and responding to the specific antigen. This process forms a critical component of the adaptive immune system, providing a targeted and potent defense against a wide range of infectious agents.
explain CD8+ cytotoxic T cells
CD8+ T Cell Response to Endogenous Antigens:
CD8+ T cell activation is triggered when they interact with pathogenic antigen fragments presented on the cell surface via MHC class I molecules.
MHC Class I Presentation of Endogenous Antigens:
MHC class I molecules are expressed on the surfaces of most nucleated cells in the body.
These molecules are specialized in presenting “endogenous” antigens, which are antigens synthesized inside host cells.
A common example is when a virus infects a host cell. The virus enters the host cell and starts expressing its genetic material (DNA or RNA) to synthesize viral proteins (antigens) within the cell.
Antigen Processing:
Once viral proteins (endogenous antigens) are synthesized inside the infected cell, they are subjected to proteolytic enzymes. These enzymes break down the proteins into smaller antigen fragments.
Antigen-MHC Class I Complex Formation:
The generated antigen fragments then bind to MHC class I molecules within the infected cell.
Cell Surface Presentation:
The antigen-MHC class I complexes are transported to the cell surface and displayed there.
CD8+ T Cell Recognition:
CD8+ cytotoxic T cells, also known as killer T cells, patrol the body and actively scan the surfaces of host cells.
When CD8+ T cells encounter a host cell displaying an antigen-MHC class I complex that matches their T cell receptor (TCR), they become activated.
Immune Response:
Activated CD8+ T cells have the ability to recognize and eliminate host cells that are infected with intracellular pathogens, including viruses. They do this by releasing cytotoxic molecules that induce apoptosis (programmed cell death) in the infected cells.
This process ensures that infected host cells are selectively targeted for destruction while sparing uninfected neighboring cells. It is a crucial mechanism for controlling intracellular infections and preventing the spread of pathogens.
explain the CD8+ T cell response to an antigen
CD8+ T Cell Response to Antigen:
Recognition of Antigen-MHC Class I Complex: CD8+ T cells, also known as cytotoxic T cells, survey the body for cells displaying antigens presented on MHC class I molecules. These antigens are typically derived from endogenous sources, such as viral proteins synthesized within the host cell.
Activation of CD8+ T Cells: When CD8+ T cells encounter a host cell displaying an antigen-MHC class I complex that matches their T cell receptor (TCR), they become activated. This activation is initiated by the binding of the TCR to the antigen-MHC complex.
Release of Cytotoxic Granules: Activated CD8+ T cells release cytotoxic granules, which are small vesicles containing molecules with cytolytic properties. The main cytotoxic granules secreted by CD8+ T cells include perforin and granzymes.
Perforin-Mediated Pore Formation: Perforin is a protein that forms pores or channels in the membrane of the infected host cell. These pores allow the entry of granzymes and other cytotoxic molecules into the target cell.
Granzyme-Induced Target Cell Destruction: Granzymes are enzymes that induce cell death. They enter the infected cell through the perforin-created pores and trigger apoptosis, a form of programmed cell death. Apoptosis leads to the demise of the infected cell.
Limiting Viral Spread: CD8+ T cells play a critical role in limiting the spread of intracellular pathogens, such as viruses, by directly eliminating infected cells. This process helps contain the infection and prevent further viral replication.
The ability of CD8+ T cells to selectively destroy infected cells while sparing uninfected neighboring cells is essential for effective immune responses against intracellular pathogens. This mechanism helps control infections and contributes to the immune system’s ability to combat a wide range of pathogens.
explain CD4+ T cells
CD4+ T Cell Response to Antigen:
Recognition of Antigen-MHC Class II Complex: CD4+ T cells, often referred to as helper T cells, continuously survey the body for antigen-presenting cells (APCs) that display antigens on MHC class II molecules. These antigens are typically derived from exogenous sources, such as bacteria, viruses, or other extracellular pathogens.
Activation of CD4+ T Cells: When CD4+ T cells encounter an APC presenting an antigen-MHC class II complex that matches their T cell receptor (TCR), they become activated. This activation is initiated by the binding of the TCR to the antigen-MHC complex.
Coordinating Immune Responses: Activated CD4+ T cells play a central role in orchestrating the immune response. They release signaling molecules called cytokines, which serve as messengers to communicate with other immune cells. CD4+ T cells can differentiate into different subsets, such as Th1, Th2, and Th17 cells, each of which helps regulate specific aspects of the immune response.
Stimulating B Cells: CD4+ T cells help B cells by providing the necessary signals for their activation and differentiation. This interaction leads to the production of antibodies by plasma cells, a process known as humoral immunity.
Enhancing Cytotoxic T Cell Activity: CD4+ T cells also facilitate the activation and function of CD8+ cytotoxic T cells, enhancing the body’s ability to combat intracellular pathogens by directly eliminating infected cells.
Regulating Inflammation: CD4+ T cells can promote or dampen inflammation based on the type of response required to deal with a particular infection. This regulation helps avoid excessive immune reactions, such as autoimmune responses.
Coordinating the Immune Memory: CD4+ T cells contribute to the establishment of immunological memory. By instructing B cells and cytotoxic T cells, they enable a faster and more effective response upon subsequent encounters with the same pathogen.
explain the CD4+ T cell response to an antigen
Recognition of Antigen-MHC Class II Complex: CD4+ T cells continually survey the body for antigen-presenting cells (APCs) that display antigens on MHC class II molecules. These antigens are typically derived from exogenous sources, such as bacteria, viruses, or other extracellular pathogens.
Activation of CD4+ T Cells: When CD4+ T cells encounter an APC presenting an antigen-MHC class II complex that matches their T cell receptor (TCR), they become activated. This activation is initiated by the binding of the TCR to the antigen-MHC complex.
Release of Cytokines: Activated CD4+ T cells release various cytokines, such as interleukins (ILs). These cytokines serve as signaling molecules that orchestrate the immune response. The specific types of cytokines released can vary based on the immune needs of the body.
Coordinating Immune Responses: The released cytokines play a central role in directing and regulating the immune response. Helper T cells can differentiate into different subsets, such as Th1, Th2, and Th17 cells, each of which has specific functions. For example:
Th1 cells promote the activation of macrophages and cytotoxic T cells, helping combat intracellular pathogens.
Th2 cells are involved in promoting antibody production by B cells, aiding in humoral immunity.
Th17 cells play a role in recruiting neutrophils to sites of infection and inflammation.
Enhancing Immune Cell Activation: The cytokines released by CD4+ T cells activate various immune cells, including macrophages, neutrophils, cytotoxic T cells, and B cells. This activation helps optimize the immune response to clear the pathogen.
Regulating Inflammation: CD4+ T cells play a crucial role in the regulation of inflammation. They help coordinate the balance between pro-inflammatory and anti-inflammatory responses, ensuring an appropriate immune reaction without excessive tissue damage.
Supporting Immunological Memory: CD4+ T cells contribute to the establishment of immunological memory.
