Immune Response to Fungal Recognition

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Questions and Answers

What activates innate effector cells upon recognition of fungi?

Receptor signaling (correct)

Adaptive immune responses

Antigen presentation

Cytokine production

Which adaptive immune responses are generated from the recognition of fungi?

Th2 and Th17 responses

Th1 and Th17 responses (correct)

Th1 and Th2 responses

Th1 and Th0 responses

Which receptor is specifically mentioned as recognizing fungi?

TLR4

Dectin-1 (correct)

CD4

Dectin-3

What is the primary role of Dectin-2 in the immune system's response to fungi?

Pathogen recognition (B) Signup and view all the answers

Which immune pathway is activated through the recognition of fungal elements?

Innate immunity (C) Signup and view all the answers

What is one function of pili in pathogens?

Attachment to host cells (C) Signup and view all the answers

What is antigenic drift primarily caused by?

Natural mutations over time (A) Signup and view all the answers

How does Borrelia burgdorferi evade the immune response?

By binding complement protein factor H (A) Signup and view all the answers

What role does molecular mimicry play in immune response evasion?

It prevents immune recognition of self-peptides. (B) Signup and view all the answers

Which pathogen is known to express a single functional copy of the pilin gene?

Neisseria species (D) Signup and view all the answers

What specific mechanism do pathogens often use to resist phagocytosis?

Production of capsular polysaccharides (C) Signup and view all the answers

What is the mutation rate of a wild-type E. coli per genome per generation?

Approximately 1 × 10−3 (A) Signup and view all the answers

What do the Osp proteins produced by Borrelia burgdorferi bind to?

Complement protein factor H (A) Signup and view all the answers

What mechanism enables fungal pathogens to replicate and spread within the host?

Persistence within phagocytes (B) Signup and view all the answers

Which immune response is primarily responsible for tissue damage during a fungal infection?

Inflammation (A) Signup and view all the answers

Which of the following cells are principal mediators of the innate immune response against fungal pathogens?

Neutrophils (A) Signup and view all the answers

Which receptor type is a C-type lectin receptor that recognizes fungal cell wall components?

Dectin (B) Signup and view all the answers

What role does IL-12 play in the immune response to intracellular bacteria?

Activates NK cells (A) Signup and view all the answers

What role do neutrophils play in responding to fungal pathogens?

They phagocytose fungal cells and release reactive oxygen intermediates. (D) Signup and view all the answers

Which statement about dendritic cells in the context of fungal infections is true?

They express PRRs that recognize fungal components. (C) Signup and view all the answers

How do cytotoxic T cells (CTLs) eliminate infected cells?

Through perforin and granzymes (D) Signup and view all the answers

Which mechanism allows Listeria monocytogenes to evade the immune response?

Degrading phagosomal membrane with LLO (A) Signup and view all the answers

In combating fungal infections, the immune system's response mainly involves which of the following?

Cell-mediated immune responses (A) Signup and view all the answers

What cytokines are secreted by sentinel macrophages and dendritic cells to recruit neutrophils?

Chemokines (C) Signup and view all the answers

What is the primary response of macrophages to ingested intracellular bacteria they cannot kill?

Secretion of IL-12 (A) Signup and view all the answers

What function does the protein ActA serve in Listeria monocytogenes?

Propels the bacterium through host cell actin (A) Signup and view all the answers

What effect does activation of NK cells have during the immune response?

It produces IFN-γ to activate macrophages (A) Signup and view all the answers

Which of the following best describes the adaptive immune response to intracellular bacteria?

Primarily cell-mediated immunity (C) Signup and view all the answers

Which type of immune cell is primarily responsible for activating macrophages through IFN-γ secretion?

NK cells (D) Signup and view all the answers

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

Activating phagocytosis and complement (A) Signup and view all the answers

Which mechanism do some intracellular bacteria use to resist the immune response?

Escape from the phagosome (C) Signup and view all the answers

How do endotoxins from gram-negative bacteria contribute to immune activation?

Cause release of pro-inflammatory cytokines (B) Signup and view all the answers

Which of the following is considered part of the innate immune response to extracellular bacteria?

Phagocytosis and complement activation (A) Signup and view all the answers

What type of response do antibodies primarily provide against extracellular bacterial infections?

Humoral immune response (A) Signup and view all the answers

What is the role of antimicrobial peptides in the innate immune response?

Directly kill bacteria by disrupting their membranes (A) Signup and view all the answers

Which bacterium prevents the fusion of the phagosome with lysosomes during an immune response?

Mycobacterium tuberculosis (D) Signup and view all the answers

Which of the following statements about the role of antibodies is incorrect regarding intracellular bacteria?

Antibodies directly eliminate intracellular bacteria (A) Signup and view all the answers

What is the primary immune response to intracellular fungi?

Th1 and CTLs (A) Signup and view all the answers

Which immune cells are primarily stimulated by cytokines from dendritic cells in response to fungal pathogens?

Innate effector cells (A) Signup and view all the answers

What is one evasion tactic used by fungal pathogens to resist the immune system?

Biofilm formation (A) Signup and view all the answers

Which type of immune response is mainly involved in combating extracellular fungi?

Th17 responses that recruit neutrophils (B) Signup and view all the answers

What roles do antibodies play in the immune response to fungal pathogens?

Neutralization, opsonization, and activation of complement (C) Signup and view all the answers

What does the term 'anti-fungal PRRs' refer to?

Pathogen recognition receptors that specifically react to fungal elements (B) Signup and view all the answers

Which immune response correlates with the activation of Th1 and Th17 cells?

Response to fungal infections (D) Signup and view all the answers

How do fungi typically mask their antigens from the immune system?

By modifying their cell wall composition and organization (A) Signup and view all the answers

Study Notes

Pathogens

Pathogen: A bacterium, virus, or other microorganism that can cause disease
Opportunistic Pathogen: A microorganism that causes disease in people with weakened immune systems, but not in healthy individuals.
Pathogenicity: Actions taken by an organism to circumvent innate immunity and inflict damage.

Evasion of Immunity

The immune system is highly adapted to combat invaders.
Mammals appeared roughly 210 million years ago, while the first prokaryotic cells appeared around 4 billion years ago.
The statement, "Never underestimate an adversary with a 3.5-billion-year head start" highlights the significant evolutionary history of pathogens.

Non-pathogens

Most E. coli strains are harmless residents of the mammalian microbiota.
E. coli K12 synthesizes vitamin B6 and coenzyme B12.
It does not produce toxins and lacks virulence factors.

Pathogens (cont.)

Enteropathogenic and Enterotoxigenic Escherichia coli (EPEC and ETEC) cause diarrheal diseases in animals (and humans).
ETEC has multiple toxins.
EPEC possesses virulence factors for host epithelial cell colonization.

Innate Immunity and Microbiota

Mammals are colonized with thousands of bacterial species that coexist in harmony (symbiosis).
In the colon, there are roughly 10¹² bacterial cells and they are able to breach the mucosal barrier, but innate immunity usually responds swiftly, before the need for adaptive immunity.
Inflammatory bowel disease is an adaptive immune response to microbiota.

Immune Response to Pathogens

Pathogens cause direct damage by killing host cells or toxin release.
Immune responses to pathogens can contribute to tissue damage and disease indirectly.

How the Immune System Responds

The immune system responds to non-pathogens, intracellular bacterial pathogens, extracellular bacterial pathogens, and fungal pathogens in different ways.

Pathogens Evade Responses

Pathogens evade immune responses through various mechanisms.
- Antigenic or Phase Variation
- Antigenic Drift
- Molecular Mimicry
- Virulence Factors

Antigenic/Phase Variation

A change in promoter arrangement alters the expression levels of flagellin protein — such as in salmonella.
Pili functions include attachment to host cells and motility.
Pili are composed of a highly antigenic protein known as pilin.
Neisseria species often have a single functional pilin gene (pilE) and many silent copies of a different pilin gene (pilS).

Antigenic Drift

Natural mutations over time lead to altered proteins that become targets of antibodies.
The mutation rate of a wild-type E. coli is approximately 1 × 10^-3 per genome per generation.

Molecular Mimicry

Sequence similarities between foreign and self-peptides may result in a lack of an antibody response to the antigen or cross-reactive immune responses.
For instance, Campylobacter jejuni shares similarities with GM1 ganglioside in nerve cell membranes.

Virulence Factors

Borrelia burgdorferi (causes Lyme disease) resists complement-mediated phagocytosis.
Osp proteins within its outer membrane bind complement protein factor H.
C3b binding to factor H inactivates it.

Other Evasive Strategies

Possession of a capsule by some bacterial pathogens resists phagocytosis and inhibits complement activation.
- Streptococcus suis, for example, secretes sIgA proteases.
- Many bacteria secrete IgA proteases to inactive sIgA.
- Fab and Fc fragments of antibodies have short half-lives at the mucosal surface.

Intracellular Bacteria

Listeria monocytogenes causes gastroenteritis in mammals.
- It produces Listeria lysin O(LLO) that degrades phagosomal membranes.
- It replicates in the cytoplasm and utilizes host cell actin to propel to new cells.
- The immune response involves phagocytosis and NK cell activity.
- Macrophages secrete IL-12 to trigger an immune response.
- IL-12 activates NK cells for specific actions.
- Activated NK cells secrete IFN-y that enhances macrophage activity and directly kills infected cells with downregulated class I MHC molecules.
- Adaptive immunity involves CD8 T cells (cytotoxic T cells).
- Activated CTLs kill infected cells via perforin and granzymes, or Fas-FasL interaction.
- Antibodies can play a limited role against intracellular bacteria by binding to bacterial antigens on infected cell surfaces to initiate ADCC or activate complement and phagocytosis.

Extracellular Bacteria

Mechanisms of pathogenesis include the release of toxins like endotoxin (LPS), which activates macrophages and causes cytokine release and complement activation in gram-negative bacteria.
- Gram-positive bacteria may have lipoteichoic acid in their cell walls with similar functions.
- Exotoxins stimulate cytokine release or are cytotoxic to certain cells.
Atrophic rhinitis in swine is also related to exotoxin function of bacteria Bordetella brontisceptica and Pasteurella multocida.
- Disrupts cellular signaling, thus disrupting bone formation.
Innate immune responses involve physical barriers, antimicrobial peptides like lysozyme, and defensins.
- Extracellular pathogens lead to inflammation, the activation of complement, and phagocytosis.
- Anaphylatoxins and pro-inflammatory cytokines drive inflammation.
Adaptive immune responses involve antibodies. Antibodies neutralize microbes and toxins, opsonize microbes for phagocytosis, activate complement, and lead to antibody-dependent cell-mediated cytotoxicity.

Fungal Pathogens

Fungal diseases use similar mechanisms to bacterial diseases.
Persistence within phagocytes is a common tactic.
- Increased replication within phagocytes can increase the spread of the pathogen.
Inflammation leads to tissue destruction at the site of infection, along with other systemic effects.
Cytotoxic T-cell (CTL) activity also damages tissues.
Innate response involves neutrophils, macrophages, and dendritic cells that secrete cytokines and release ROS, lysosomal enzymes, and NETS upon recognizing fungal components.
Adaptive responses are characterized by cell-mediated immunity, initially stimulated by cytokines from dendritic cells, and use of T helper cells with particular cytokine profiles to target fungal pathogens inside or outside cells.
Antibodies neutralize fungi, opsonize them for phagocytosis, activate complement, and lead to antibody-dependent cell-mediated cytotoxicity -- similar to how the immune response acts against bacteria.
- Evasion tactics for fungal pathogens include biofilm formation, altered cell-wall composition, masking of antigens, acquisition of nutrients, and production of proteins to inactivate antimicrobial peptides.

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Description

Test your understanding of the immune system's response to fungal infections. This quiz covers innate and adaptive immune responses, key receptors involved, and the specific roles of Dectin-2. Perfect for students studying immunology or related fields.