Immunity to Infection Chapter 13
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Questions and Answers

What type of immune response is primarily associated with the defense against helminth infections?

  • Th2 responses (correct)
  • Cytotoxic T-cell responses
  • Th1 responses
  • Innate immune responses

Which mechanism is commonly used by parasites to evade the host immune response?

  • Molecular mimicry (correct)
  • Cytokine release
  • T-cell activation
  • Antibody production

What is a common characteristic of fungal infections relating to human immunity?

  • They do not elicit any immune response.
  • They are usually eliminated by neutrophils.
  • They primarily target the liver.
  • They might trigger a hyperactive immune response. (correct)

What defines a prion disease?

<p>A condition caused by misfolded proteins. (B)</p> Signup and view all the answers

How do immunocompromised individuals respond to infections compared to healthy individuals?

<p>Their immune response may be diminished. (A)</p> Signup and view all the answers

Which of the following is NOT typically linked to Th2 responses?

<p>Increased macrophage activation (A)</p> Signup and view all the answers

What is the role of cytokines in the context of fungal infections?

<p>They recruit immune cells to the site of infection. (D)</p> Signup and view all the answers

In terms of immune evasion, how can some parasites protect themselves from host defenses?

<p>By altering their surface proteins (A)</p> Signup and view all the answers

What is the primary immune response required to eliminate helminth worms?

<p>Th2 responses (D)</p> Signup and view all the answers

Which mechanism is commonly used by parasites to evade the immune system?

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

Which fungal species is particularly threatening to immunocompromised individuals?

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

In the context of protozoan infections, what role does IFN-g involving CTLs play?

<p>It contributes significantly to anti-protozoan responses (C)</p> Signup and view all the answers

How do dimorphic fungi differ in their structure during their life cycle?

<p>They switch between unicellular and multicellular forms (C)</p> Signup and view all the answers

What does TLR4 play a crucial role in combating?

<p>Helminth worms like Schistosoma mansonii (A)</p> Signup and view all the answers

What immune challenge do fungi pose particularly to individuals undergoing chemotherapy?

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

Which immune response is primarily ineffective during the early stages of protozoan infections?

<p>Perforin/granzyme-mediated cytolysis (B)</p> Signup and view all the answers

What is the role of Th1 responses in anti-protozoan defense?

<p>They are key sources of IFN-g needed for macrophage hyperactivation. (C)</p> Signup and view all the answers

Which mechanism is NOT primarily associated with humoral defense against protozoans?

<p>Viral replication inhibition. (D)</p> Signup and view all the answers

How does IFN-g contribute to the immune defense against protozoan parasites?

<p>By inducing iNOS expression leading to nitrogen oxide production. (D)</p> Signup and view all the answers

What is the consequence of hyperactivated macrophages failing to clear a protozoan infection?

<p>They form a granuloma around the infected cells. (A)</p> Signup and view all the answers

Which of the following cytokines is associated with Th2 responses, contributing to susceptibility to protozoan infections?

<p>IL-10 (B)</p> Signup and view all the answers

Which is a function of antibodies in defense against small extracellular protozoans?

<p>Facilitation of opsonized phagocytosis. (D)</p> Signup and view all the answers

What is a potential effect of Th2 cytokines on macrophage function during protozoan infections?

<p>Inhibiting the production of IFN-g. (D)</p> Signup and view all the answers

Which type of immune cell is primarily involved in ADCC against larger extracellular protozoans?

<p>Neutrophils and macrophages. (D)</p> Signup and view all the answers

Which strategy do fungi use to evade immune detection by pattern recognition receptors (PRRs)?

<p>Changing their morphological forms (A)</p> Signup and view all the answers

What principal characteristic differentiates prions from other pathogens?

<p>Transmissible proteins without nucleic acid (D)</p> Signup and view all the answers

How do misfolded prion proteins affect healthy proteins in the host?

<p>By converting them into more prion proteins (D)</p> Signup and view all the answers

What is a common outcome of prion infections in the brain?

<p>Destruction of neuronal tissue (A)</p> Signup and view all the answers

What role do T cells have in response to prion infections?

<p>They display tolerance towards PrPres proteins (A)</p> Signup and view all the answers

What is the primary reason that viruses depend on host cells for replication?

<p>Viruses lack the necessary components for protein assembly. (D)</p> Signup and view all the answers

What classification is used for viral diseases based on their duration?

<p>Acute and chronic. (C)</p> Signup and view all the answers

Which of the following describes a potential outcome when a virus becomes latent?

<p>It can lead to severe disease upon reactivation. (B)</p> Signup and view all the answers

How can the immune response to a viral infection cause damage to host tissues?

<p>Via inflammation and immunopathic disease. (B)</p> Signup and view all the answers

What is a common mechanism by which progeny virions spread to other host cells?

<p>Binding to host surface receptors. (D)</p> Signup and view all the answers

Which factor can influence the severity of acute viral diseases?

<p>The virulence of the virus. (C)</p> Signup and view all the answers

What role do viral pathogen-associated molecular patterns (PAMPs) play in viral infections?

<p>They trigger immune recognition and response. (C)</p> Signup and view all the answers

What happens to host cells that are infected by viruses?

<p>They are usually destroyed or inactivated. (A)</p> Signup and view all the answers

What is the process by which a virus changes its antigenic epitopes over successive generations?

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

Which type of immune response is typically induced by protozoan parasites?

<p>Th1 responses (B)</p> Signup and view all the answers

How do helminth worms primarily reproduce in relation to their host?

<p>Extracellularly but inside the host's body (C)</p> Signup and view all the answers

Which immune component is activated by certain stages of Plasmodium species to produce interferons?

<p>Plasmacytoid dendritic cells (pDCs) (C)</p> Signup and view all the answers

Which of the following parasites uses a mosquito as a vector for transmission?

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

What is a common mechanism for fighting Plasmodium falciparum aside from immune cell activation?

<p>Complement activation via the MBL-induced lectin pathway (D)</p> Signup and view all the answers

Which type of immune response is typically associated with helminth worm infections?

<p>Th2 responses (B)</p> Signup and view all the answers

Which characteristic is typical of antigenic shift in viruses?

<p>Major reassortment of viral genetic material (B)</p> Signup and view all the answers

What role does IFN-g play during protozoan infections?

<p>Enhances CTL and gd T cell responses (A)</p> Signup and view all the answers

Which immune response is primarily necessary for combating helminth worms?

<p>Th2 response (C)</p> Signup and view all the answers

What is a key mechanism of immune evasion used by pathogenic parasites?

<p>Avoiding phagolysosomal destruction (B)</p> Signup and view all the answers

Why are fungi a significant clinical threat to immunocompromised individuals?

<p>They often induce immunosuppression (B)</p> Signup and view all the answers

What characteristic do dimorphic fungi exhibit?

<p>They can switch between unicellular and multicellular forms (B)</p> Signup and view all the answers

What does perforin/granzyme-mediated cytolysis primarily target during chronic protozoan infections?

<p>Infected host cells (A)</p> Signup and view all the answers

Which TLR is crucial for inducing innate defenses against Schistosoma mansonii?

<p>TLR4 (A)</p> Signup and view all the answers

What phase of the immune response is represented by the activity of gd T cells in protozoan infections?

<p>Early stages of infection (A)</p> Signup and view all the answers

What is a crucial effect of Th1 responses in anti-protozoan defense?

<p>Production of IFN-g necessary for macrophage hyperactivation (C)</p> Signup and view all the answers

How do antibodies contribute to the defense against small extracellular protozoans?

<p>Mediate opsonization, neutralization, and complement activation (B)</p> Signup and view all the answers

Which statement about macrophage hyperactivation is correct?

<p>It results in the production of reactive oxygen and nitrogen intermediates. (C)</p> Signup and view all the answers

What role does TNF secreted by hyperactivated macrophages play in protozoan infections?

<p>It significantly contributes to the control of protozoan infections. (A)</p> Signup and view all the answers

What is the consequence of a Th2 response dominating over a Th1 response?

<p>Heightened susceptibility to diseases caused by protozoan parasites. (D)</p> Signup and view all the answers

Which of the following is a consequence of IFN-g production by Th1 cells?

<p>Stimulating IL-12 production by dendritic cells and macrophages. (C)</p> Signup and view all the answers

Which mechanism is employed to eliminate larger extracellular protozoans?

<p>Antibody-dependent cell-mediated cytotoxicity (ADCC) (C)</p> Signup and view all the answers

What is one of the effects of iNOS expression in infected macrophages?

<p>It helps kill the parasites or infected cells. (B)</p> Signup and view all the answers

Which mechanism is used by fungi to elude host immune response by interfering with T helper cell functions?

<p>Promoting a less effective Th response (A)</p> Signup and view all the answers

What is the primary characteristic that distinguishes prions from other infectious agents?

<p>They are transmissible proteins (A)</p> Signup and view all the answers

In the context of prion diseases, what clinical effect does PrPres have on the host's normal prion protein (PrPc)?

<p>It refolds PrPc into more PrPres (C)</p> Signup and view all the answers

What is one of the major challenges that prions pose to the immune system during infection?

<p>Host tolerance to the infectious PrPres protein (D)</p> Signup and view all the answers

Which statement best describes the method by which fungi can avoid detection by pattern recognition receptors (PRRs)?

<p>By altering their morphological forms (C)</p> Signup and view all the answers

What is primarily responsible for the replication of viruses within a host cell?

<p>Host cell's enzymes (D)</p> Signup and view all the answers

What can be a consequence of a virus becoming latent in a host?

<p>Reactivation triggering acute disease (A), Chronic infections without symptoms (D)</p> Signup and view all the answers

How does the immune response to viral infections primarily challenge host tissues?

<p>By inducing inflammation (D)</p> Signup and view all the answers

Which of the following describes the mechanism by which progeny virions spread to other host cells?

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

What factor is primarily included in determining the severity of an acute viral disease?

<p>The virulence of the virus (C)</p> Signup and view all the answers

What is one of the fundamental roles of viral pathogen-associated molecular patterns (PAMPs) during infections?

<p>Activating host immune defenses (B)</p> Signup and view all the answers

What is a potential effect of the immune response against viral infections?

<p>Immunopathology leading to tissue damage (A)</p> Signup and view all the answers

What distinguishes acute viral diseases from chronic ones?

<p>Acute diseases are typically short-term, while chronic ones persist (A)</p> Signup and view all the answers

What role does IFN-g play in the immune response to protozoan infections?

<p>It assists in the activation of CTLs and boosts anti-protozoan responses. (A)</p> Signup and view all the answers

Which type of immune response is critical for eliminating helminth worms?

<p>Th2 responses (D)</p> Signup and view all the answers

What mechanism is important for controlling the chronic stages of protozoan infections?

<p>Perforin/granzyme-mediated cytolysis (B)</p> Signup and view all the answers

What is one potential method used by protozoan parasites to evade the immune response?

<p>Avoiding antibody detection (D)</p> Signup and view all the answers

How do dimorphic fungi adapt during their life cycle?

<p>By switching between unicellular and multicellular forms. (C)</p> Signup and view all the answers

Which of the following fungal species poses a notable threat to those with weakened immune systems?

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

Which innate immune component has been identified as important for combating Schistosoma mansonii?

<p>TLR4 (C)</p> Signup and view all the answers

What is a significant clinical implication of fungal infections for individuals undergoing certain medical treatments?

<p>Heightened risk of invasive infections due to immunosuppression (A)</p> Signup and view all the answers

What process describes the minor modifications of viral antigens through random mutations over generations?

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

What type of immune responses do helminth worms usually evoke during infections?

<p>Th2 responses (D)</p> Signup and view all the answers

Which immune mechanism is notably activated during Plasmodium falciparum infections?

<p>Complement activation via MBL-induced lectin pathway (C)</p> Signup and view all the answers

Which stage of Plasmodium species specifically produces PAMPs that trigger interferon production?

<p>Sporozoite stage (C)</p> Signup and view all the answers

What strategy do viruses commonly use to avoid detection by the host immune system?

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

What describes the accommodation of various hosts by parasites during their life cycle?

<p>Multistage life cycles (D)</p> Signup and view all the answers

Which type of immune response is generally less effective against protozoan parasites during their early infection stages?

<p>Th2 responses (B)</p> Signup and view all the answers

How do protozoan parasites typically replicate in relation to their host cells?

<p>Both intracellularly and extracellularly (A)</p> Signup and view all the answers

What is the role of anti-parasite antibodies in defending against small extracellular protozoans?

<p>Mediating neutralization and opsonization (B)</p> Signup and view all the answers

What is the primary mechanism by which hyperactivated macrophages eliminate protozoan parasites?

<p>Generating reactive oxygen intermediates and reactive nitrogen intermediates (B)</p> Signup and view all the answers

What consequence occurs if hyperactivated macrophages cannot clear a protozoan infection?

<p>Development of a granuloma around the infected cells (C)</p> Signup and view all the answers

How does IFN-g affect dendritic cells and macrophages in the context of anti-protozoan defense?

<p>Stimulates IL-12 production (C)</p> Signup and view all the answers

What is the primary function of TNF secreted by hyperactivated macrophages?

<p>Contributing to the control of protozoans (B)</p> Signup and view all the answers

What effect do Th1 cytokines have on the immune response to protozoan parasites?

<p>They facilitate macrophage activation and IFN-g production. (A)</p> Signup and view all the answers

What consequence arises from the presence of larger extracellular protozoans in relation to the immune response?

<p>They are effectively dealt with by neutrophil-mediated ADCC. (A)</p> Signup and view all the answers

Flashcards

Viral Structure

Viruses are intracellular pathogens with a nucleic acid genome (DNA or RNA) enclosed in a protein capsid. Some may have a membrane envelope.

Viral Replication

Viruses depend on host cells for replication, using host enzymes to produce new virions (viral particles).

Viral Dissemination

New viral particles released by infected cells spread to other cells, potentially throughout the body.

Acute Viral Disease

A short-term viral infection that resolves relatively quickly.

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Chronic Viral Infection

A persistent viral infection that lasts a long time, possibly recurring or causing long-term illness.

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Viral Latency

A state where a virus remains dormant in the body without causing symptoms, potentially reactivating later.

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Immune Response to Viruses

The body's immune response to viral infection can sometimes cause tissue damage, inflammation, and immunopathic disease.

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Viral Pathogenesis

Viruses cause disease either directly by damaging host cells or indirectly through provoking an overwhelming immune response.

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Humoral defense against protozoans

Antibodies target small extracellular protozoans through neutralization, opsonization, and complement activation.

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ADCC for larger protozoans

Larger extracellular protozoans are destroyed by antibody-dependent cell-mediated cytotoxicity involving neutrophils and macrophages.

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Th1 responses in anti-protozoan defense

Th1 cells produce IFN-g, activating macrophages to kill intracellular protozoans.

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Macrophage hyperactivation

Enhanced macrophage activity to produce reactive oxygen and nitrogen intermediates needed to kill protozoan parasites.

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Granuloma formation

A defensive structure formed by macrophages when hyperactive macrophages can't eliminate the parasite, isolating the infection.

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IFN-g's anti-protozoan effects

IFN-g directly kills parasites, boosts IL-12, induces NO production, enhances phagosome maturation, and increase Fas expression in infected macrophages.

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Th2 responses and protozoan susceptibility

Th2 cytokines inhibit IFN-g production and suppress iNOS, making individuals more susceptible to protozoan diseases.

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SNPs and Malaria susceptibility

Variations in single nucleotide polymorphisms (SNPs) in TLRs, complement receptors, and CRP can influence resistance or susceptibility to malaria.

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CTLs role in protozoan infection

CTLs (cytotoxic T lymphocytes) target infected host cells, releasing IFN-γ, which plays a crucial role in combating protozoan infections. Perforin/granzyme-mediated cytolysis is less effective during acute infections but becomes more important during chronic ones.

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gd T cells and protozoa

Activated gd T cells secrete IFN-γ, supporting the body's defenses during the initial stages of protozoan infections.

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Helminth defense mechanism

Induced innate (TLR4) and Th2 immune responses are important in destroying helminth worms, but the exact mechanisms are not fully understood.

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Parasite immune evasion

Parasites avoid or interfere with the host's immune responses in several ways, including by avoiding antibodies, phagolysosomes, complement, and potentially manipulating host T-cell responses.

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Fungal infection types

Fungi can be unicellular (yeast) or multicellular (mycelium). Some fungi (dermatophytes) specifically infect skin, hair, and nails. Many more fungal types present a clinical threat to immunocompromised individuals.

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Immune response to fungi

Most fungal species aren't harmful, but become invasive in immunocompromised individuals, like those undergoing organ transplants, autoimmune treatments, or chemotherapy.

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Th1 vs Th2

Th1 responses are crucial for combating protozoan parasites, while Th2 responses are important against helminth (worm) parasites.

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Immune evasion by parasites

Parasites can use strategies to avoid the immune system, including avoiding antibodies, phagolysosomes, complement, and modulating T-cell responses.

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Viral Entry

Viruses enter a host cell by attaching to a specific surface receptor, allowing them to enter and replicate within the cell.

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Viral Spread

Newly produced viral particles spread to neighboring cells, potentially leading to widespread infection within the body.

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Acute vs. Chronic Viral Infection

Acute viral infections are short-lived and usually resolve quickly, while chronic infections persist over long periods and may cause recurring illnesses.

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Immune Effector Mechanisms for Viral Defense

Immune mechanisms against viruses include the destruction of viral particles by phagocytosis or clathrin-mediated endocytosis, as well as the recognition and activation of immune cells by viral PAMPs.

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Viral Evasion Strategies

Viruses have evolved strategies to evade the immune system by suppressing immune responses, hiding from immune cells, mutating to avoid recognition, or interfering with immune signaling.

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Antigenic Drift

A gradual change in a virus's antigens due to random mutations during replication. This makes it harder for the immune system to recognize and fight the virus.

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Antigenic Shift

A sudden, major change in a virus's antigens that can occur when two different viruses mix, creating a new, potentially more dangerous strain.

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How do viruses evade the immune system?

Viruses use various strategies to avoid the immune system, including changing their antigens (antigenic drift and shift), suppressing immune responses, and hiding within cells.

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What is the role of Th1 responses in parasitic infections?

Th1 responses are important for fighting protozoan parasites. Th1 cells produce IFN-γ, which activates macrophages to kill intracellular parasites.

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What is the role of Th2 responses in parasitic infections?

Th2 responses are important for fighting helminth worms. Th2 cells produce cytokines that help expel worms from the body.

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How do parasitic infections impact the immune system?

Different parasites trigger different immune responses. Protozoans often induce Th1 responses, while helminths typically induce Th2 responses.

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What is the role of complement in protozoan infections?

Complement activation, specifically through the lectin pathway, is important for fighting Plasmodium falciparum and other malaria-causing Plasmodium species.

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How do parasites evade the immune system?

Parasites can evade the immune system using various strategies, including hiding within cells, mimicking host molecules, and suppressing immune responses.

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SNPs and Malaria

Variations in single nucleotide polymorphisms (SNPs) within genes such as TLRs, complement receptors, and CRP can influence an individual's susceptibility or resistance to malaria.

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Macrophage Hyperactivation: Killing Parasites

Activated macrophages produce increased levels of reactive oxygen and nitrogen intermediates, essential for effectively killing protozoan parasites.

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Granuloma Formation: Wall Off Infection

If hyperactive macrophages cannot completely eliminate a parasite, they form a 'granuloma', a defensive structure that encapsulates infected cells and isolates the infection.

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IFN-γ: Many Anti-Protozoan Roles

IFN-γ has multiple roles in fighting protozoans, including directly killing them, stimulating IL-12 production, inducing NO production, enhancing phagosome maturation, and increasing Fas expression in infected macrophages.

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ADCC (Antibody-Dependent Cell-Mediated Cytotoxicity)

Larger extracellular protozoans can be eliminated by antibody-dependent cell-mediated cytotoxicity (ADCC) involving neutrophils and macrophages.

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Fungal Evasion Strategies

Fungi have evolved various mechanisms to avoid immune detection and destruction, including hiding from PRRs, resisting phagocytosis, evading complement, modulating T cell responses, and blocking antibody binding.

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How do fungi avoid detection by PRRs?

Fungi can modify their surface molecules to avoid recognition by pattern recognition receptors (PRRs) on immune cells, making them 'invisible' to the immune system.

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What is the role of complement in fungal defense?

Complement proteins can help to kill fungi by forming membrane attack complexes (MACs) and triggering opsonization. However, some fungi can evade complement activation.

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How do fungi manipulate T cell responses?

Some fungi can promote a less effective T cell response (Th2) by suppressing Th1 responses, which are important for fighting intracellular infections.

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Why are antibodies less effective against fungi?

Fungi can evade antibodies by hiding within host cells, producing antigenic variation, or creating a capsule that shields them from antibody binding.

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CTLs and Protozoa

Cytotoxic T lymphocytes (CTLs) target cells infected with protozoan parasites. They release IFN-γ, which is crucial for controlling infections, especially during the early stages. Perforin/granzyme-mediated cytolysis is less effective during acute infections but becomes more important in chronic stages.

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Th2 Response and Helminths

Th2 responses are essential for combating helminth (worm) infections. They produce cytokines that help eliminate these parasites.

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TLR4 and Schistosoma

TLR4 is an important immune receptor involved in fighting Schistosoma mansonii, a blood-dwelling trematode. It plays a role in initiating the defense against this helminth.

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Fungal Infections in Immunocompromised Individuals

Though most fungi are harmless, they can become invasive and dangerous in individuals with weakened immune systems, like those undergoing organ transplants, autoimmune treatments, or chemotherapy.

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Fungal Types

Fungi can be either unicellular (like yeast) or multicellular (like mycelia, with hyphae). Some types, called dermatophytes, specifically infect the skin, hair, and nails.

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Dimorphic Fungi

Some fungi can exist in both unicellular (yeast) and multicellular (mycelia) forms at different stages of their life cycle.

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Acute Viral Infection

A short-term viral infection that resolves quickly, often with mild symptoms. The immune system effectively fights off the virus.

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Th2 responses for helminth defense

Th2 responses are essential for fighting helminth (worm) infections by producing cytokines that help expel these parasites from the body.

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Parasite immune evasion strategies

Parasites can evade the immune system by hiding within cells, mimicking host molecules, and suppressing immune responses to ensure their survival.

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Macrophage hyperactivation for killing parasites

Activated macrophages produce increased levels of reactive oxygen and nitrogen intermediates, essential for effectively killing protozoan parasites.

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SNPs in Immunity

Variations in single nucleotide polymorphisms (SNPs) in immune system genes, like TLRs, complement receptors, and CRP, can influence susceptibility to diseases like malaria.

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Th1 Response: Protozoan Defense

Th1 immune response is crucial for combating protozoan parasites. Th1 cells produce IFN-gamma, activating macrophages to kill intracellular parasites.

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Macrophage Hyperactivation: Killing Protozoa

Activated macrophages produce increased levels of reactive oxygen and nitrogen intermediates, crucial for effectively killing protozoan parasites inside them.

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IFN-gamma: Multiple Anti-Protozoan Roles

IFN-gamma has several functions in fighting protozoans. It can directly kill them, stimulate IL-12 production, induce NO production, enhance phagosome maturation, and increase Fas expression in infected macrophages.

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Th2 Response: Helminth Defense

Th2 immune response is important for fighting helminth (worm) infections. Th2 cells produce cytokines that help expel these parasites from the body.

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TLR4: Key Defense in Helminth Infections

TLR4, a pattern recognition receptor, is involved in fighting Schistosoma mansonii, a blood-dwelling trematode. It plays a vital role in initiating the defense against this parasitic worm.

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Prion infection

A rare, fatal neurodegenerative disease caused by infectious proteins called prions that cause the brain to become sponge-like. Prions can be transmitted through ingestion of infected tissue.

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PrPres protein

The misfolded form of the prion protein that is infectious. It acts as a template for changing the normal PrPc protein into more PrPres, leading to disease.

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How do fungi avoid PRRs?

Fungi can evade detection by the immune system by altering their surface molecules to avoid being recognized by pattern recognition receptors (PRRs) on immune cells.

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What is the role of T cells in prion infection?

In cases of prion infection, T cells are usually tolerant to the infectious PrPres protein, meaning they don't attack it. This contributes to the lack of an effective adaptive immune response against prions.

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What is the role of complement in fungal infections?

Complement proteins can help kill fungi by forming membrane attack complexes (MACs) and triggering opsonization. However, some fungi have evolved to evade complement activation.

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Evasion by Parasites

Parasites can evade the immune system using various strategies, including hiding within cells, mimicking host molecules, and suppressing immune responses.

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Study Notes

Chapter 13: Immunity to Infection

  • The lecture outlines immunity to viruses, viral evasion strategies, immunity to protozoa, immunity to helminths and parasites, immunity to fungi, and immunity to prions.

Immunity to Viruses: Disease Mechanisms

  • Viruses are intracellular pathogens that consist of a nucleic acid genome packaged in a protein coat (capsid).
  • The viral genome can be DNA or RNA.
  • Viral capsids may or may not have an envelope.
  • Most viruses enter host cells by binding to surface receptors.
  • Virus replication can be carried out by host or viral enzymes, depending on the virus.
  • Viruses lack their own protein synthesis machinery and depend on host cellular machinery for protein translation and assembly.
  • Progeny virions from infected host cells attack nearby cells, leading to widespread virus dissemination.
  • Progeny virions reaching the blood can spread systemically.
  • Viruses cause disease directly or indirectly by killing or inactivating host cell functions.
  • Symptoms arise when host cells are significantly affected.
  • Immune responses to viral infections often damage host tissue and induce inflammation, leading to immunopathic diseases.
  • Viral diseases are classified as acute or chronic.
  • Initial viral infection may be mild or severe depending on the virus' virulence and duration.
  • Some viruses establish persistent infections, causing long-term or recurrent illnesses (chronic diseases).
  • Some viruses become latent without causing disease but reactivate later, causing more significant disease (e.g., Varicella-zoster virus (VZV) causing chicken pox in children and shingles in adults).

Innate Immune Effector Mechanisms

  • The mechanisms involve clathrin-mediated endocytosis or phagocytosis of virions or activation by viral PAMPs.
  • Natural killer (NK) cell activation by interferon alpha/beta (IFNα/β).
  • Macrophage activation by interferon gamma (IFNγ).

Adaptive Immune Effector Mechanisms

  • CD4+ T cell activation.
  • Antibody-mediated phagocytosis.
  • CTL Activation.

Viral Evasion Strategies

  • Viruses can alter viral epitopes (antigenic drift or shift) to evade antibody detection.
  • Viruses sometimes inhibit complement activation.
  • Viruses may evade CD8+ T cells by decreasing MHC-I expression.
  • Viruses may evade CD4+ T cells by interfering with MHC-II-mediated antigen presentation.

Antigenic Variation

  • Antigenic variation is a common viral evasion strategy.
  • Antigenic drift involves minor modifications to viral antigens through random mutations.
  • Antigenic shift involves major changes in viral antigens due to reassortment of RNA segments

Evasion Strategies of Viruses (Specific examples)

  • NK cells: Express viral homologs of MHC class I to avoid detection or increase HLA-E.
  • DCs: Block DC development or maturation and regulate DC expression.
  • Complement: Block convertase formation, express virus homologs of host proteins, bud through the host membranes, acquire host RCA proteins.
  • Host PRRs: Produce proteins interfering with normal PRR signaling or low CpG motifs.
  • Antiviral state: Block IFN secretion, interfere with metabolic/enzymatic events.
  • Apoptosis: Block steps of extrinsic or intrinsic pathways, express homologs of death receptors, express regulatory molecules, sustain host cell survival.
  • Cytokines/chemokines: Express competitive inhibitors, block cytokine/chemokine transcription, block cytokine/chemokine translation or downregulate receptor expression.

Immunity to Parasites

  • Parasites include unicellular protozoa and multicellular worms.
  • Protozoa can reproduce extracellularly or intracellularly.
  • Helminth worms reproduce inside or outside host cells.
  • Parasites frequently use vectors to infect hosts.
  • Different parasite types evoke different immune responses.
  • Protozoa typically stimulate Th1 responses.
  • Helminth infections commonly stimulate Th2 responses.

Defense Against Protozoans

  • Innate defenses: Protozoan components activate TLRs. Stages of Plasmodium activate plasmacytoid DCs (pDCs). Complement activation via MBL-induced lectin pathways is vital against malaria. Single nucleotide polymorphisms (SNPs) in TLRs, complement receptors, or acute phase proteins influence resistance.
  • Humoral defenses: Antibody-mediated neutralization, opsonization, and phagocytosis or classical complement activation work against extracellular protozoans. Larger extracellular protozoa are cleared using antibody-dependent cellular cytotoxicity (ADCC) mediated by neutrophils/macrophages.
  • Th1 responses and macrophage hyperactivation: Crucial for eliminating intracellular protozoa, which often persist inside macrophages. IFN-γ is vital for macrophage activation.
  • Th2 responses are susceptible to protozoan diseases.

Defense Against Helminth Worms

  • Innate defenses: In mice, TLR4 plays a role in fighting blood-dwelling trematodes (e.g., Schistosoma mansonii).
  • Th2 responses and humoral defenses are essential for eliminating helminths. Th2 responses, along with antibodies (e.g., IgE) and mast cell activation, are key to eliminating these parasites.

Immunity to Fungi

  • Fungi can be unicellular or multicellular (hyphae) and form a mass (mycelium).
  • Dimorphic fungi switch between cellular and multicellular forms in their life cycles.
  • Dermatophytes fungi commonly infect skin, hair, and nails.
  • Most fungal species are harmless but can become invasive and cause significant problems in immunocompromised individuals.

Evasion Strategies used by Fungi

  • Avoiding detection by pattern recognition receptors (PRRs), phagocyte activation, or complement activation.
  • Promoting less effective Th responses.
  • Avoiding antibodies.

Immunity to Prions

  • Prions are misfolded proteins involved in neurodegenerative diseases.
  • Prions trigger more prions to be produced by acting as templates.
  • Prions lead to the destruction of the brain without inducing any significant adaptive response.
  •  Recent evidence suggests innate defenses may play a role in combating prion diseases.

Next Lecture Topic:

  • Chapter 18: Immune Hypersensitivity.

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Lecture 30: Immunity to Infection (Kaushik 2024) PDF

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This quiz covers various aspects of immunity to infections, including responses to viruses, protozoa, helminths, parasites, fungi, and prions. Gain insights into how these pathogens evade the immune system and the mechanisms behind viral infections. Perfect for understanding the complexities of immune responses in human health.

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