11.3 Immunity to Bacteria and Fungi

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Questions and Answers

What is the primary pathological consequence of severe infection by certain bacteria leading to sepsis?

Systemic tissue edema

Localized inflammation

Direct bacterial tissue invasion

Organ dysfunction and systemic disorders (correct)

Which cytokines are primarily involved in mediating sepsis?

IL-2, IL-10, and TNF

IL-8, IL-12, and TGF-beta

IFN-gamma, IL-4, and IL-6

IL-1, IL-6, and TNF (correct)

How do bacteria evade humoral immunity through antigenic variation?

By producing superantigens that distract the immune response

By releasing toxic enzymes that degrade antibodies

By altering surface antigens to escape specific antibody recognition (correct)

Through the formation of biofilms that block immune access

What is a disease that can arise from an immune response after streptococcal infections?

Glomerulonephritis Signup and view all the answers

What characteristic helps certain bacteria resist phagocytosis?

Polysaccharide-rich capsules Signup and view all the answers

What is the primary role of humoral immunity in response to extracellular bacteria?

To block infection, eliminate microbes, and neutralize toxins Signup and view all the answers

Which cytokines are primarily secreted by innate lymphoid cells (ILCs) to attract neutrophils during inflammation?

IL-17 and IL-22 Signup and view all the answers

Which cell type is crucial for stimulating antibody production in response to extracellular bacteria?

CD4+ helper T cells Signup and view all the answers

What are the injurious effects of inflammation in response to extracellular bacteria primarily caused by?

Local production of reactive oxygen species (ROS) and lysosomal enzymes Signup and view all the answers

Which IgG subclasses are primarily involved in the immune response against extracellular bacteria?

IgM, IgG1, and IgG3 Signup and view all the answers

What is the primary mechanism of innate immunity against extracellular bacteria?

Complement activation Signup and view all the answers

Which of the following statements best describes extracellular bacteria?

They can replicate outside host cells. Signup and view all the answers

What is one way that pathogens can injure host tissues during infection?

By releasing toxins Signup and view all the answers

How do microbes typically evade host immunity?

By resisting destruction by immune mechanisms Signup and view all the answers

Which immune response role do phagocytes play in combating extracellular bacteria?

They recognize and engulf bacteria. Signup and view all the answers

What is a mechanism through which extracellular bacteria can induce tissue damage?

By inducing apoptosis in host cells Signup and view all the answers

What consequence can arise when the immune response controls but does not eliminate a microbe?

Latent infection Signup and view all the answers

What types of organisms do microbes encompass in the context of immune response mechanisms?

Bacteria, viruses, fungi, and parasites Signup and view all the answers

What cytokine is known to provide protective effects in many protozoal infections?

IFN-γ Signup and view all the answers

Which immune response is primarily activated against helminthic infections?

Activation of Th2 cells Signup and view all the answers

What is the role of IgE in the defense against helminths?

It coats the parasites allowing eosinophils to bind and release their granules. Signup and view all the answers

What is the mechanism of immune evasion exhibited by parasites through antigen variation?

Stage-specific change in antigen expression and continuous variation of major surface antigens Signup and view all the answers

What specifically activates eosinophils during the immune response to helminthic infections?

IL-5 Signup and view all the answers

What is the main mechanism of antigenic variation in influenza viruses?

Reassortment Signup and view all the answers

Which of the following best describes the role of MHC class I molecules?

Presenting cytosolic protein antigens to CD8+ T cells Signup and view all the answers

What effect does chronic viral infection have on cytotoxic T lymphocyte responses?

Results in exhaustion of CTL responses Signup and view all the answers

Why are parasitic infections often chronic?

Weak innate immunity and ability to evade immune responses Signup and view all the answers

What is the principal innate immune response to protozoa?

Phagocytosis Signup and view all the answers

Which type of cells contribute to the innate immune response against helminths?

Eosinophils Signup and view all the answers

What adaptive immune response is primarily activated against protozoa that survive within macrophages?

Cell-mediated immunity Signup and view all the answers

How do some viruses inhibit the immune response?

By encoding soluble cytokine receptors Signup and view all the answers

What is the primary mechanism by which intracellular bacteria are recognized by the innate immune system?

Recognition by TLRs and NOD-like receptors Signup and view all the answers

Which immune cells play a significant role in mediating the adaptive immune response against intracellular bacteria?

CD4+ T cells and phagocytes Signup and view all the answers

What is a common consequence of macrophage activation in response to intracellular bacteria?

Tissue injury Signup and view all the answers

What type of immune cells are primarily responsible for killing virally infected cells in the adaptive immune response?

CD8+ cytotoxic T lymphocytes Signup and view all the answers

Which of the following cytokines are crucial for activating NK cells in response to intracellular bacteria?

IL-15 and IL-12 Signup and view all the answers

How do antibodies primarily function in the immune response to viral infections?

By neutralizing viruses and blocking their entry Signup and view all the answers

What role do type I interferons (IFNs) play in the immune response to viral infections?

They inhibit viral replication in both infected and uninfected cells Signup and view all the answers

Which immune response is primarily triggered against extracellular fungal infections?

Th17 response Signup and view all the answers

What characterizes many fungal infections in terms of patient immunity?

They are often opportunistic in immunocompromised patients Signup and view all the answers

What is a common feature of immune evasion strategies employed by intracellular bacteria?

They promote chronic infections and resistance to elimination Signup and view all the answers

What is the primary function of humoral immunity in response to extracellular bacteria?

To block infections and neutralize toxins Signup and view all the answers

Which cell type is primarily responsible for enhancing phagocytic activity against extracellular bacteria?

CD4+ helper T cells Signup and view all the answers

What is one of the injurious effects of inflammation caused by host responses to extracellular bacteria?

Tissue damage from reactive oxygen species (ROS) Signup and view all the answers

Which cytokines are secreted by ILCs to promote neutrophil attraction during inflammation?

IL-17 and IL-22 Signup and view all the answers

Which immunoglobulin isotype provides a high-affinity response against extracellular bacteria and helps neutralize toxins?

IgG Signup and view all the answers

What is a key factor determining the pathogenicity of microbes in a host?

Their ability to evade host immune responses Signup and view all the answers

What specific type of bacteria are defined as extracellular bacteria?

Bacteria that replicate outside host cells Signup and view all the answers

Which mechanism is primarily responsible for the phagocytosis of extracellular bacteria?

Complement receptor engagement Signup and view all the answers

What role do toxins produced by extracellular bacteria play during an infection?

Causing tissue damage and derangements Signup and view all the answers

How do microbes typically cause tissue injury upon infection?

By directly killing host cells or releasing harmful toxins Signup and view all the answers

What role does IL-4 play in the immune response to helminthic infections?

Stimulates the production of IgE antibodies Signup and view all the answers

What is the main effector mechanism of innate immunity against extracellular bacteria?

Complement activation and phagocytosis Signup and view all the answers

How do eosinophils contribute to the defense against helminths during an immune response?

They release their granule contents to destroy helminths Signup and view all the answers

Which of the following describes a characteristic of latent infections caused by some microbes?

The immune response controls but does not eliminate the microbe Signup and view all the answers

What initiates the complement activation in response to extracellular bacteria?

Peptidoglycans in Gram-positive bacteria and LPS in Gram-negative bacteria Signup and view all the answers

What is an example of antigenic variation in parasites?

Distinct antigen expression between sporozoite and merozoite stages in malaria Signup and view all the answers

What is the primary action of the cytokine IFN-γ in protozoal infections?

Enhances Th1 cell responses Signup and view all the answers

Which cells are primarily responsible for mediating the immune response against helminthic infections?

Th2 cells Signup and view all the answers

What is a primary mechanism viruses use to change their antigens and escape immune responses?

Reassortment Signup and view all the answers

Which of the following best describes how some viruses inhibit class I MHC molecule functions?

By blocking transport and processing of cytosolic proteins Signup and view all the answers

What is a consequence of chronic viral infections on cytotoxic T lymphocyte (CTL) responses?

Exhaustion of CTL responses Signup and view all the answers

What type of immune response is primarily activated against helminths?

Humoral immunity Signup and view all the answers

What is the principal immune response mechanism utilized by eosinophils against helminths?

Degranulation Signup and view all the answers

Which cytokines are common targets for viral proteins that inhibit the immune response?

IFN-γ, TNF, IL-1, IL-18 Signup and view all the answers

What is the primary role of TLR2 and TLR4 in the immune response to protozoa?

Recognition and detection leading to phagocytosis Signup and view all the answers

What mechanism do parasites typically utilize to survive within the host immune system?

Antigenic variation Signup and view all the answers

What severe condition can arise as a result of sepsis?

Septic shock Signup and view all the answers

Which of the following is a mechanism by which bacteria escape the immune response?

Variation of surface antigens Signup and view all the answers

What is a common consequence of the immune response to streptococcal infections?

Glomerulonephritis Signup and view all the answers

Which substance is primarily secreted by macrophages during sepsis to mediate systemic disorders?

Tumor necrosis factor (TNF) Signup and view all the answers

How do bacteria with polysaccharide-rich capsules affect immune response?

Resist phagocytosis Signup and view all the answers

What is the primary mechanism required for eliminating intracellular bacteria?

Cell-mediated immunity Signup and view all the answers

Which immune cells are mainly responsible for the innate response to fungal infections?

Neutrophils and macrophages Signup and view all the answers

What is the primary action of CD4+ T cells in the context of intracellular bacteria?

Activating phagocytes Signup and view all the answers

Which process do type I interferons inhibit in virus-infected cells?

Viral replication Signup and view all the answers

Which immune response is triggered primarily by extracellular fungi?

Th17 response Signup and view all the answers

How do CD8+ cytotoxic T lymphocytes (CTLs) contribute to viral infection control?

Inducing apoptosis in infected cells Signup and view all the answers

What role do natural killer (NK) cells play in antiviral immunity?

Killing infected cells directly Signup and view all the answers

What consequence can arise from macrophage activation in response to intracellular pathogens?

Tissue injury Signup and view all the answers

Which immune component is primarily responsible for blocking virus entry into host cells?

Antibodies Signup and view all the answers

What is a characteristic of intracellular bacteria that contributes to chronic infections?

Resistance to phagocyte-mediated elimination Signup and view all the answers

Study Notes

Immunity to Pathogens

Study objectives include understanding infection and immune response mechanisms to pathogens (bacteria, viruses, fungi, and parasites), injurious effects of immune responses, and pathogen immune evasion.

Development of Infectious Disease

Important events in infection include microbe entry, invasion and colonization of host tissues, evasion of host immunity, and tissue injury/functional impairment.

Microbes and Disease Production

Microbes cause disease through direct killing of host cells, releasing toxins causing tissue damage/functional derangements, or stimulating immune responses that can injure normal tissues.

Progression and Outcomes of Infections

Infection progression involves an incubation period, followed by a disease phase where the immune response controls the infection, resulting in either no disease, recurrent illness, or eradication with full recovery if the host response is strong enough.

Overview of Immune Responses to Pathogens

Immunity is mediated by innate and adaptive effector mechanisms.
The immune system employs specific responses to combat different pathogens.
Pathogen survival relies on evasion or resistance to the host's immune response.

Latent/Persistent Infections

Some microbes establish latent or persistent infections where the immune response controls but does not eliminate the pathogen.

Inherited/Acquired Defects in Immunity

Defects in innate and adaptive immunity increase susceptibility to infections.

Immunity to Extracellular Bacteria

Extracellular bacteria replicate outside host cells (e.g., blood, connective tissue).
They induce inflammation and produce toxins damaging tissues.

Innate Immunity to Extracellular Bacteria

Complement activation is crucial, triggered by peptidoglycans in gram-positive bacteria and lipopolysaccharides (LPS) in gram-negative bacteria through the alternative pathway.
Mannose-expressing bacteria activate the lectin pathway.
Phagocytes use mannose/scavenger receptors, Fc receptors, and complement receptors to recognize and engulf bacteria.

Phagocytosis

Phagocytes (e.g., neutrophils, macrophages) use mannose/scavenger receptors, Fc receptors, and complement receptors to recognize and engulf bacteria.

Inflammatory Response

Phagocytes and dendritic cells secrete cytokines and inflammation mediators to induce leukocyte infiltration.

Adaptive Immunity to Extracellular Bacteria

Humoral immunity is a major protective response.
Antibodies neutralize toxins, opsonize bacteria for phagocytosis, and activate complement for bacterial destruction.

CD4+ Helper T cells

Helper T cells produce cytokines that enhance phagocytic and microbicidal activities of macrophages/neutrophils, as well as stimulate antibody production.

Outcomes of Immune Responses to Extracellular Bacteria

Inflammation is often self-limiting but can cause tissue damage.
Sepsis is a severe systemic consequence of infections, leading to potentially fatal outcomes.

Polyclonal Activation of T cells

Bacterial superantigens can cause polyclonal T cell activation, stimulating cytokine storm and T cell deletion.

Disease-Producing Antibodies

Antibodies produced against bacteria can cross-react with host tissues resulting in conditions like myocarditis and glomerulonephritis.

Immune Evasion by Extracellular Bacteria

Bacteria can vary their surface antigens to avoid recognition and antibody-mediated clearance.
Bacteria often have capsules obstructing phagocytosis.
Some pathogenic bacteria produce components preventing complement activation.

Immunity to Intracellular Bacteria

Intracellular bacteria survive and replicate within phagocytes.
Antibody responses are ineffective since they cannot access the bacteria.
Cell-mediated immunity is critical to fight and eliminate the infection.

Innate Immunity to Intracellular Bacteria

Phagocytes/ natural killer (NK) cells are the primary mediators.
Toll-like receptors (TLRs) and Nod-like receptors (NLRs) recognize the bacteria to activate phagocytes.
Cytokines (e.g., IL-12, IL-15) activate NK cells.

Adaptive Immunity to Intracellular Bacteria

Cell-mediated immunity (CD4+/CD8+ T cells) is the main protective response.
CD4+ cells activate phagocytes/others, resulting in elimination.
CD8+ cytotoxic T lymphocytes(CTLs) kill infected cells.

Immune Evasion by Intracellular Bacteria

Bacteria use mechanisms to impede phagolysosome formation.
Bacteria may inhibit reactive oxygen/nitrogen species to prevent death.
Escape from phagosomes or inhibition of phagolysosome formation is a common mechanism for evasion.

Immunity to Fungi

Fungal infections, known as mycoses, are often opportunistic in immunocompromised individuals.
Fungi can be extracellular or intracellular.

Innate and Adaptive Immunity to Fungi

Neutrophils, macrophages, and ILCs mediate innate responses.
TLRs/lectin-like receptors (dectins) recognize fungal components.
Cytokines stimulate neutrophils/ILCs/phagocytes directly or indirectly.

Cell-Mediated Immunity to Fungi

Adaptive immunity (CD4+/CD8+ T cells) actively combat fungi.
CTLs kill fungus-infected cells; CD4+ cells activate phagocytes.

Immunity to Viruses

Viruses are intracellular pathogens depending on host cells.
Replication mechanisms disrupt normal cellular function, resulting in cytopathic effects on host cells.
Both innate and adaptive immune pathways work in concert to resolve the infection.

Innate Immunity to Viruses

The principal innate immunity mechanisms are inhibition of infection by type I interferons and the killing of infected cells by NK cells (natural killer cells).
Virus-infected cells/dendritic cells secrete type I interferons (IFNs). These interfere with viral replication inside and outside the infected cells.
NK cells kill infected host cells.

How Type I Interferons Block Virus Replication

Type I interferons (IFNs) induce the expression of antiviral proteins.
These proteins stop viral replication by hindering gene expression/protein synthesis.

Adaptive Immunity to Viruses

Antibodies are crucial in the extracellular stage of viral infection.
Antibodies bind to viral surface antigens, neutralizing them.
Antibodies also promote phagocytosis.
CTLs eliminate infected cells.

Elimination of Viruses in Cells

Cytotoxic T lymphocytes (CTLs) eliminate viruses by killing infected cells.

Immune Evasion by Viruses

Antigenic variation where viruses alter their surface antigens to evade immune recognition is a common method of immune evasion.
Inhibition of MHC molecules, which affects cytosolic protein antigen presentation.
Inhibition of the immune response where some viruses produce molecules that inhibit immune responses, such as soluble cytokine receptors or inhibition of interferon responses.

Immunity to Parasites

Parasites include protozoa, worms(helminths), and ectoparasites.
Complex life cycles often require multiple hosts.
Parasitic infections are frequently chronic, with the immune responses frequently being less effective than in other infections and often not successfully clearing the infection.

Innate Immunity to Parasites

Phagocytes are a critical component.
Protozoan parasites are often resistant to phagocytosis.

Adaptive Immunity to Parasites

Antibodies and CD8+ cells.
CD4/Th1 cells activate macrophages to help kill parasites by phagocytosis.
Th2 cells play a role in antibody production and eosinophil activation for helminth infections.

Antigenic Variation in Parasites

Stage-specific and continuous variations are observed, which allow parasites to evade the host immune responses.

• Defense against helminthic infections involves Th2 cell activation, resulting in IgE antibody production and eosinophil activation. .

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Description

Test your knowledge on the immune responses to bacterial infections, focusing on cytokines, humoral immunity, and the mechanisms of sepsis. This quiz covers the complex interactions between pathogens and the host's immune system, highlighting key concepts in immunology.