Host-Pathogen Interactions Overview
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Questions and Answers

What is the primary role of fever in the immune response?

  • To enhance the immune response by speeding up metabolism and phagocyte activity (correct)
  • To promote the activation of B cells
  • To inhibit the production of cytokines
  • To directly kill pathogens through temperature increase

    • Which immune response mechanism is primarily involved in dealing with intracellular bacteria?

  • Inhibition of surface antigen variability
  • Phagocytosis and killing in the phagolysosome (correct)
  • Activation of complement
  • Neutralization by antibodies

    • What characterizes the adaptive immune response against extracellular bacteria?

  • Release of eosinophils and IgE production
  • Type I interferons and NK cell activation
  • Phagocytosis and T cell activation
  • Neutralization by antibodies and complement activation (correct)

    • Which aspect of the immune response is primarily promoted by the complement system?

    <p>Enhancement of inflammation and clearance of microbes (D)</p> Signup and view all the answers

    Which immune response primarily addresses fungal infections?

    <p>Phagocytosis and neutrophil activity (A)</p> Signup and view all the answers

    What mechanism do viruses employ to evade the host immune response?

    <p>Surface antigens variability through mutations (B)</p> Signup and view all the answers

    What defines a pathogen as opposed to normal flora in host-microbe interactions?

    <p>Pathogens are capable of causing host damage. (A)</p> Signup and view all the answers

    Which type of microorganism is characterized by being obligate parasites that cannot replicate outside host cells?

    <p>Viruses (D)</p> Signup and view all the answers

    Which of the following is NOT a recognized type of pathogen affecting human hosts?

    <p>Bacilli (A)</p> Signup and view all the answers

    What may result from an asymptomatic carrier status in host-microbe interactions?

    <p>Potential source of infection (A)</p> Signup and view all the answers

    Which component is considered part of the host's innate immunity?

    <p>Sensing receptors (B)</p> Signup and view all the answers

    What is the role of phagocytosis in the host's defense against pathogens?

    <p>It eliminates pathogens through engulfment. (D)</p> Signup and view all the answers

    Which of the following pathogens typically has a complex life cycle?

    <p>P.falciparum (A)</p> Signup and view all the answers

    How do pathogens commonly invade host tissues?

    <p>Via adherence to receptors (D)</p> Signup and view all the answers

    What is a primary characteristic of helminths as pathogens?

    <p>They exhibit simple to complex life cycles. (B)</p> Signup and view all the answers

    What role do pathogen associated molecular patterns (PAMP) play in the immune system?

    <p>They act as ligands for pattern recognition receptors. (A)</p> Signup and view all the answers

    What is the main function of the surface barriers in the immune system?

    <p>To keep pathogens from entering host tissues. (A)</p> Signup and view all the answers

    Which of the following components is considered a part of innate immunity?

    <p>Normal flora. (A)</p> Signup and view all the answers

    Which statement accurately reflects adaptive immunity?

    <p>It is characterized by specificity and memory. (A)</p> Signup and view all the answers

    What are antigenic epitopes recognized by?

    <p>T cell receptors and B cell receptors. (A)</p> Signup and view all the answers

    Which type of immunity is primarily activated by the presence of antigens?

    <p>Adaptive immunity. (C)</p> Signup and view all the answers

    What is the significance of commensal microbiota in immune defense?

    <p>They compete with pathogens for resources. (D)</p> Signup and view all the answers

    Which immune response mechanism is characterized by its ability to specifically target and remember pathogens?

    <p>Adaptive immunity. (A)</p> Signup and view all the answers

    What can lead to opportunistic infections in a host?

    <p>Immune suppression. (D)</p> Signup and view all the answers

    What is the primary purpose of immune suppression in the context of pathogens?

    <p>To promote vulnerability to opportunistic infections. (A)</p> Signup and view all the answers

    Prions are small, proteinaceous infectious particles that contain a nucleic acid genome.

    <p>False (B)</p> Signup and view all the answers

    Viruses can replicate independently outside of host cells.

    <p>False (B)</p> Signup and view all the answers

    The immune system consists of barriers that include physical, chemical, and biological defenses.

    <p>True (A)</p> Signup and view all the answers

    Helminths are characterized as single-celled prokaryotic organisms.

    <p>False (B)</p> Signup and view all the answers

    Asymptomatic carriage refers to a pathogen that remains active and causes noticeable symptoms in the host.

    <p>False (B)</p> Signup and view all the answers

    Pathogen associated molecular patterns (PAMP) are unique to each individual pathogen and do not interact with host recognition molecules.

    <p>False (B)</p> Signup and view all the answers

    Adaptive immunity includes both B cells and T cells, which play critical roles in responding to specific antigens.

    <p>True (A)</p> Signup and view all the answers

    The three lines of defense in the immune system include only biological barriers.

    <p>False (B)</p> Signup and view all the answers

    Normal flora in the body can help protect against colonization by pathogens through competition and production of toxic components.

    <p>True (A)</p> Signup and view all the answers

    The innate immune response is characterized by its ability to recognize specific pathogens and develop long-lasting immunity.

    <p>False (B)</p> Signup and view all the answers

    Cytokines play a crucial role in mediating communication between immune cells during an immune response.

    <p>True (A)</p> Signup and view all the answers

    Antigens are substances that do not activate immune responses in the body.

    <p>False (B)</p> Signup and view all the answers

    Virulence factors are essential for the survival of pathogens in the environment but not necessary for infection.

    <p>False (B)</p> Signup and view all the answers

    Memory in adaptive immunity allows for a faster and more effective response upon subsequent exposures to the same antigen.

    <p>True (A)</p> Signup and view all the answers

    Surface barriers such as intact skin and mucosa act as a first line of defense against invading pathogens by keeping them outside host tissues.

    <p>True (A)</p> Signup and view all the answers

    Flashcards

    Host-microbe interaction

    The relationship between a human body and microorganisms, including beneficial (normal flora) and harmful (pathogens).

    Pathogens

    Microbes that cause host damage through direct actions or immune response.

    Normal flora

    Microbes that live in specific areas of the body in a stable way and benefit the host.

    Bacteria

    Single-celled prokaryotic organisms with cell walls.

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    Viruses

    Small, obligate parasites needing a host cell to replicate.

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    Immune system

    The body's defense against pathogens; organs, cells, and molecules.

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    Innate immunity

    The body's first line of defense against pathogens, involving sensing receptors, phagocytosis, and microbicide activity.

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    Contagious potential

    Factor influencing the spread of a pathogen, determined by various aspects such as inoculum size, transmission mode, and entry site.

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    Host defenses

    The barriers (physical, chemical, biological) and immune system mechanisms (cells, molecules) that protect the body from pathogens.

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    Innate Immune Response

    The body's first line of defense against pathogens, triggered by the binding of PRRs (Pattern Recognition Receptors) to PAMPs (Pathogen-Associated Molecular Patterns).

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    Complement System

    Part of the innate immune system that enhances the ability of antibodies and phagocytic cells to clear pathogens, promoting inflammation, and attacking the pathogen's cell membrane.

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    Phagocytes

    Immune cells that engulf and destroy pathogens (e.g., neutrophils, macrophages, dendritic cells).

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    Adaptive Immunity vs. Innate Immunity

    The nature of the invader determines the optimal (best-suited) immune response, whether it be innate or adaptive.

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    Extracellular Bacteria

    Bacteria that reside outside of host cells. Examples include neutralization by antibodies, complement activation, opsonization, phagocytosis.

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    CTL (Cytotoxic T Lymphocytes)

    A type of T cell that directly kills infected cells.

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    Antigen

    Any substance that triggers an immune response in the body to protect it from harmful entities like microbes.

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    Adaptive immunity

    A specific immune response that targets a specific antigen (part of an invader).

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    Pathogen associated molecular patterns (PAMPs)

    Conserved molecules in pathogens that trigger innate immune responses.

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    Surface barriers

    Physical, chemical, and biological barriers that keep invaders from entering the body.

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    Physical Barriers

    Intact skin and mucus membranes which prevent entry of pathogens.

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    Chemical Barriers

    Secretions like saliva, tears, stomach acid that actively block pathogens.

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    Cytokines

    Signaling proteins that regulate immune responses.

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    NK Cells (Natural Killer cells)

    Part of innate immunity, attack and destroy infected cells.

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    Antigen-presenting cells

    Cells that display antigens on their surface to activate T cells, triggering adaptive immunity.

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    Types of Pathogens

    Pathogens are microbes causing host damage; classified into bacteria, viruses, protozoa, helminths, fungi, arthropods, and prions. Each category has distinct features and infection mechanisms.

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    Outcomes of Infection

    The interaction between a host and a pathogen can lead to three outcomes: Eviction (elimination of the pathogen), Asymptomatic carriage (contained pathogen, carrier status), or Clinical symptoms (acute or chronic disease).

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    Host Defense: Barriers

    Our body has defenses against pathogens: Physical barriers (skin, mucous membranes), Chemical barriers (saliva, stomach acid), and Biological barriers (microbiota).

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    Host Defense: Immune System

    Our immune system is made up of organs, cells, and molecules that fight pathogens; It includes both innate and adaptive responses.

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    Virulence Factors

    Traits of a pathogen that determine its ability to cause disease. These factors can be direct (toxins, enzymes) or indirect (immune evasion, colonization).

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    Immune Suppression

    Weakening of the immune system, making the body more susceptible to infections, including opportunistic infections caused by weak pathogens.

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    Drug Resistance

    The ability of a pathogen to survive and proliferate despite exposure to antimicrobial drugs. Contributes to the development of untreatable infections.

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    Pathogen-Associated Antigens

    Molecules on pathogens that trigger immune responses in the host. These can be generic (PAMPs) or specific (antigenic epitopes).

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    PAMPs

    Pathogen-associated molecular patterns, conserved molecules on pathogens that bind to host pattern recognition receptors (PRRs), triggering innate immunity.

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    Antigenic Epitope

    Specific part of an antigen that is recognized by T cell and B cell receptors, triggering adaptive immunity.

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    Three Lines of Defense

    The body's defense system comprised of surface barriers (physical, chemical, biological), innate immunity, and adaptive immunity.

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    Adaptive Immunity: Memory

    A key feature of adaptive immunity where the immune system 'remembers' encountered antigens and can mount a faster and stronger response upon re-exposure.

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    Study Notes

    Host-Pathogen Interactions

    • The human body is constantly interacting with various microorganisms.
    • Some microorganisms are normal flora/microbiota, peacefully coexisting with the host for mutual benefit.
    • Other microorganisms are pathogens, capable of causing host damage via direct microbial action or inappropriate immune response.

    Types of Host-Microbe Relationships

    • Commensalism: One organism benefits, the other is neither harmed nor benefited.
    • Parasitism: One organism benefits at the expense of the other.
    • Mutualism: Both organisms benefit.

    Pathogens Affecting Human Hosts

    • Bacteria: Prokaryotic, single-celled organisms with a single DNA chromosome and cell walls (e.g., E. coli).
    • Viruses: Smaller than bacteria, with DNA or RNA genomes; obligate parasites needing host cells to replicate (e.g., CMV, HIV).
    • Protozoa: Single-celled eukaryotic organisms with organelles and simple or complex life cycles (e.g., P. falciparum, leishmania).
    • Helminths: Multicellular organisms, often worms, with simple or complex life cycles (e.g., A. lumbricoides).
    • Fungi: Eukaryotes with cell walls containing chitin or cellulose, and form spores (e.g., C. albicans).
    • Arthropods: Organisms with jointed appendages; commonly ectoparasites (e.g., S. scabiei).
    • Prions: Small proteinaceous infectious particles without nucleic acid genomes (e.g., in CJD or BSE).

    Pathogen Size Comparison

    • Images show pathogens and their comparative sizes (from meters to nanometers) relative to the naked eye, light microscope, and electron microscope.

    Types of Transmission and Their Control

    • Respiratory or salivary spreads (aerosols, saliva) are difficult to control.
    • Fecal-oral spread is controllable with public health measures.
    • Venereal spread is difficult to control due to social factors.
    • Arthropod-borne infections and zoonoses (e.g., malaria, typhus, plague) involve vectors and vertebrate reservoirs for transmission.

    Outcome of Infectious Process

    • Eviction: Pathogen elimination.
    • Asymptomatic carriage: Pathogen contained in the host, potentially leading to latent or carrier status.
    • Clinical disease: Symptoms following incubation period (acute or chronic).

    Pathogen (Invader) and Host (Defender)

    • Pathogen (Invader): Bacteria, viruses, parasites, fungi causing host damage and disease.
      • Contagious potential (inoculum size, transmission, entry, adherence, tissue invasion)
      • Virulence factors and pathogenicity (direct or indirect effects).
      • Evasion mechanisms to host immunity.
      • Acquisition of drug resistance capacity.
    • Host (Defender): Immune system (organs, cells, soluble factors).
      • Physical, chemical, and biological barriers.
      • Innate (general) immunity.
      • Adaptive (specific) immunity.
      • Immune suppression may lead to opportunistic infections.

    Pathogen-Associated Antigens

    • Antigens trigger immune responses.
    • Innate immunity, antibody formation, and T-cell-mediated immunity are activated in response to antigens.
    • Pathogen-associated molecular patterns (PAMPs).
      • Molecules found on pathogens that activate innate immune receptors (PRRs).
    • Pathogen-associated specific antigen epitope (antigenic determinant).
      • Part of an antigen recognized by adaptive T and B cells receptors.

    Organs of the Immune System

    • Immune system is located in various organs.
    • Primary organs for immune cell development are bone marrow and thymus.
    • Secondary organs for immune responses are elsewhere (e.g., spleen).

    Lymphatic Circulation

    • Lymphatic system functions in fluid transport and immune responses.

    Cells of the Immune System

    • Key immune cells (e.g., phagocytes, lymphocytes, natural killer cells) are listed with functions.

    Specific Immune Cells with Functions

    • Macrophage: Presenting antigens to helper T cells, producing cytokines (chemicals involved in cellular communication).
    • Neutrophil: Phagocytosis (engulfing pathogens).
    • Eosinophil: Kills parasites.
    • Basophil: Inflammation.
    • Mast cell: Inflammation and allergies.
    • Dendritic cell: Presenting antigens to T cells.

    Lymphocytes

    • Key role in adaptive immune responses.
    • B cells: Recognize antigens via membrane-bound antibodies; produce antibodies.
    • T cells: Coordinate immune responses and kill infected/abnormal cells.
    • Natural killer cells (NK cells): Kill stressed/unhealthy cells.

    Soluble Factors

    • Complement: Direct cell lysis (breaking down cells), enhancement of lymphocyte responses.
    • Cytokines: Cell-to-cell/tissue communication and various immune responses (e.g., inflammation, antibody production, cell growth/differentiation).
    • Interleukins: Various immune functions (inflammation and differentiation).
    • Interferons: Resistance to viral infections.
    • TNFs: Inflammation and tumor cell destruction.
    • Other chemicals: Various biochemical activities (e.g., antimicrobial actions).

    Three Lines of Defense

    • Physical, chemical, and biological barriers: Preventing pathogen entry.
    • Innate immunity: General response to destroy pathogens before they establish themselves.
    • Adaptive immunity: Specific response targeting and remembering particular pathogens.

    Surface Barriers

    • Physical barriers (intact skin).
    • Chemical barriers (secretions like saliva, tears, acidic environment).
    • Biological barriers (normal flora/microbiota).

    Innate Immunity

    • Non-specific immune mechanisms targeting pathogen elimination.
    • Binding of PRRs (Toll-like receptors) to PAMPs triggers immediate defense responses.
    • Key processes: fever, inflammation, phagocytosis, complement activation, natural killer cells.

    Inflammation

    • Response to tissue damage or infection.
    • Involves chemical signals, blood vessel changes, and immune cell migration to eliminate pathogens.

    Phagocytes

    • Cells engulf and destroy pathogens/particles.
    • Key steps include chemotaxis and adherence, ingestion, phagosome formation, phagolysosome formation and digestion, residue removal.

    Complement

    • Part of the innate immune system that enhances other immune responses.
    • Facilitates pathogen clearance, inflammation, and cell lysis (breaking down cells).

    Adaptive Immunity

    • Specific and targeted response tailored to specific pathogens encountered throughout life.
    • Key features: specificity, memory, and diversity.

    Adaptive Immunity, cont.

    • B and T cells recognize and bind to specific antigens, divide by mitosis.
    • Descendent cells recognize the same antigen.
    • T cells only recognize antigen presented by antigen-presenting cells (APC).
      • APC digest particles and display antigen in MHC complexes.

    Cell-Mediated Immunity (Cellular Immunity)

    • Processes like antigen "presenting" by macrophages to T cells activate immune responses.
    • Cytotoxic T cells kill infected/abnormal cells and coordinate helper T cell activity.

    Antibody-Mediated Immunity (Humoral Immunity)

    • Antibodies bind to antigens, facilitating phagocytosis, complement activation/lysis, and neutralizing pathogens.

    Adaptive Immunity, cont.

    • Differentiated lymphocytes (B and T cells) initiate immediate responses to fight infection.
    • B cells produce antibodies targeting specific antigens in bodily fluids; activate complement and phagocytosis or neutralize pathogens.
    • Cytotoxic T cells kill infected or abnormal cells.
    • Memory cells persist to provide a faster and stronger response to future encounters with familiar antigens.

    Primary and Secondary B Cell Responses

    • Primary response to first exposure produces effector and memory B cells.
    • Secondary response triggered by subsequent exposures is stronger and faster due to memory cells.

    Innate and Adaptive Immunity Comparison

    • Innate: Immediate response, non-specific.
    • Adaptive: Delayed response, specific.

    Nature of Invader Determines Host Immune Response

    • The type of pathogen dictates how the body responds immunologically. Different pathogens trigger different immune responses.

    Pathogen Evasion Mechanisms

    • Pathogens employ various mechanisms to evade the host's immune responses (e.g., antigenic variation, complement inhibition, evasion of phagocytosis).

    Environment: Source & Reservoir

    • Source: Site where a pathogen is transmitted.
    • Reservoir: Site where pathogens multiply.
    • Examples like humans, animals, food, water.
      • Yellow fever with monkeys as a reservoir, mosquitos as a source.

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