Immune System Microbial Detection Quiz

Immune System Danger Sensing

• The immune system must distinguish between foreign, dangerous substances, and harmless or self substances.
• Different microbes have characteristic molecules, enabling immune cells to recognise pathogens.
• Key objectives include describing how microbes are detected by immune cells and methods microbes use to avoid detection.
• Questions to consider:
  • What microbial substances activate the immune system?
  • How does the immune system recognise the damage caused by pathogens?
  • Which cells and receptors respond to microbial products?
  • What are the consequences of microbial sensing for the host?
  • How do microbes evade detection?

Initial Infection Response

• Local innate immune cells are activated.
• Blood vessel permeability increases.
• Migration of more immune cells and plasma proteins into tissues (acute inflammation).
• Immune cells involved include dendritic cells, blood vessels, macrophages, neutrophils, and monocytes.

Host Receptors

• Charles Janeway predicted host receptors recognizing conserved patterns on pathogenic molecules.
• Key researchers include Janeway, Beutler, Hoffmann, and Steinman (Nobel Prize 2011).

PAMPs

• PAMPs (Pathogen Associated Molecular Patterns) are microbial components differentiating microbes from host cells.
• Examples of PAMPs include viral nucleic acids, bacterial DNA, fungal polysaccharides, and protozoan glycolipids..

Danger Model

• Polly Matzinger argued the immune system senses danger, not just non-self.
• The system responds to damage or danger, not just foreign antigens.

DAMPs

• DAMPs (Damage-Associated Molecular Patterns) are molecules from dying cells.
• Examples include nucleic acids and cytoplasmic proteins.

Information Transfer

• Innate cells sense pathogens, and this information is passed to adaptive immune cells.
• Adaptive immune cells include CD4+ T cells (coordinate immune response), CD8+ T cells (kill infected cells), and B cells (make antibodies to eliminate pathogens).

Leukocytes and Tissue Cells

• Leukocytes (blood cells) and tissue cells (epithelial and fibroblast cells) detect and control pathogens at infection sites.
• Immune cells, like dendritic cells and macrophages, engulf pathogens to activate adaptive immune cells.
• Tissue cells, like epithelial cells, release inflammatory molecules.

Pathogen Avoidance of Complement

• Host cells and some pathogens evade complement components.
• Examples include CD46 inactivating C3b and CD59 stopping MAC formation.

Pattern Recognition Receptors (PRRs)

• PRRs recognize PAMPs and DAMPs.
• Different types of PRRs include Toll-like receptors (TLRs, mostly recognize PAMPs), Nucleotide-binding oligomerization domain-like receptors (NLRs), C-type lectin-like receptors (CLRs), and some other absent receptors.

PRR Location

• PRRs are located on cell membranes (for bacteria and fungal recognition) or inside cells in the cytoplasm (for viral, bacterial, and DAMP/PAMP sensing).

Pathogen Hiding

• Pathogens can hide from PRR recognition.
• Examples include Helicobacter pylori flagellin, poliovirus RNA, and Listeria monocytogenes altered cell walls.

Consequences of PRR Activation

• PRR activation leads to signaling to other cells, adaptive immune system activation, limiting microbe replication, and controlling pathogen presence.
• The involved mechanisms include phagocytosis, inflammation, and cytokine release.

NF-κB Activation

• Bacteria can alter gene transcription by activating NF-κB.
• TLR activation initiates intra-cellular pathways activating NF-κB.
• NF-κB activates gene transcription.

Pathogen Inhibition

• Some pathogens limit NF-κB activation, reducing the warning signal to the immune system.
• Examples include E. coli virulence factors and Shigella enzymes.

Inflammasomes

• Some NLRs form inflammasomes.
• Inflammasomes are platforms activating caspase-1.
• Inflammasomes act in the cytoplasm of cells.

Viral Infection

• Influenza virus infection causes inflammatory cytokines and cell death.
• Influenza targets respiratory tract epithelial cells.
• TLR and RIG-I signaling are involved.
• Type I IFN is released reducing viral spread.

Viral Inhibition

• Influenza virus inhibits intracellular activation of PRRs, reducing anti-viral immune responses.
• NS1 inhibits NF-κB activation.

Adaptive Responses

• Pathogens and the damage they cause trigger innate immune responses.
• This sometimes activates adaptive immune responses (e.g., vaccination, immunity).
• Pathogens can evade recognition, and sometimes, the immune response is inappropriately triggered (e.g., allergies, autoimmunity).

This quiz focuses on the immune system's ability to sense and respond to dangerous microbes. It covers the mechanisms by which immune cells identify pathogens and the strategies employed by microbes to evade detection. Explore key concepts about innate immune responses, cell activation, and the consequences for the host.