Pathogen Recognition Receptors & Innate immune Response || Toll-like Receptors

Summary

This script explains how the innate immune system detects and responds to pathogens through specialized receptors. Dendritic cells recognize pathogen-associated molecular patterns (PAMPs) using Toll-like receptors (TLRs). For instance, TLR-4 identifies lipopolysaccharides (LPS) on gram-negative bacteria. TLRs, along with NOD proteins and RNA helicase domains, detect both extracellular and intracellular pathogens, triggering immune responses. These receptors help initiate processes like dendritic cell maturation and activation of the acquired immune system. Collectively, these mechanisms allow the immune system to detect and respond to various pathogens, whether inside or outside cells.

Takeaways

• 🛡️ The innate immune system acts as the first line of defense by detecting pathogens early during an immune response.
• 🔍 Dendritic cells recognize pathogen-associated molecular patterns (PAMPs) like lipopolysaccharides (LPS) on gram-negative bacteria using Toll-like receptors (TLRs).
• 🦠 LPS is identified by TLR-4, which is expressed on the surface of dendritic cells and initiates an immune response.
• 🧬 TLRs recognize different PAMPs; for example, TLR-5 identifies flagellin, while TLR-9 detects bacterial CpG DNA after degradation in the lysosome.
• ⚙️ Upon recognition of LPS, the TLR-4 signaling stimulates dendritic cell maturation and migration to lymph nodes to activate the acquired immune response.
• 🧫 TLRs are membrane-bound proteins, some found on the cell surface and others in endocytic vesicles, where they detect pathogens taken in by endocytosis.
• 🧩 TLR-2 forms dimers with TLR-1 or TLR-6 to detect bacterial lipopeptides, while TLR-3 and TLR-7 identify viral RNA.
• ⚡ Activation of TLRs triggers transcription factors to send signals to the cell nucleus, initiating an immune response.
• 🌐 NOD proteins, like NOD2, detect intracellular bacterial components and activate immune responses through nuclear signaling.
• 🧬 The RNA helicase CARD domain family, including RIG-I, detects viral double-stranded RNA and triggers the production of Type-1 interferons to combat viral infections.

Q & A

What is the first line of defense in the immune system?

The innate immune system acts as the first line of defense by detecting pathogens through various cells like dendritic cells and macrophages.

What are pathogen-associated molecular patterns (PAMPs)?

PAMPs are conserved molecular structures found on pathogens, such as lipopolysaccharides (LPS) in gram-negative bacteria, that are recognized by the immune system.

How do dendritic cells recognize PAMPs?

Dendritic cells recognize PAMPs using Toll-like receptors (TLRs), which detect specific components of pathogens. For example, TLR-4 detects LPS in gram-negative bacteria.

What role does the CD14 protein play in detecting LPS?

CD14, along with the LPS-binding protein (LBP), helps transport LPS to the dendritic cell surface, where it is recognized by TLR-4, leading to the activation of the immune response.

What happens when a TLR detects a PAMP like LPS?

When a TLR detects a PAMP like LPS, it triggers a signaling cascade that leads to dendritic cell maturation and the activation of the acquired immune response.

Where are Toll-like receptors (TLRs) located within immune cells?

Some TLRs are located on the cell surface, where they detect extracellular pathogens, while others are found in endocytic vesicles, where they detect degraded pathogens.

What is the role of TLR-5 in pathogen detection?

TLR-5 recognizes flagellin, a conserved protein found in bacterial flagella, enabling the immune system to detect bacteria that use flagella for movement.

Which TLRs recognize RNA from viruses, and where are they found?

TLR-3 and TLR-7 recognize double-stranded RNA and single-stranded RNA, respectively. They are located in endocytic vesicles and detect viral RNA after the virus is degraded.

How do NOD proteins contribute to immune detection?

NOD proteins, such as NOD2, are cytosolic receptors that detect intracellular bacterial components like muramyl dipeptide, triggering an immune response inside the cell.

What is the role of the RIG-I protein in the immune response?

RIG-I is a cytosolic receptor that detects double-stranded RNA, a byproduct of many RNA viruses, and triggers the production of Type-1 interferons to combat viral infections.