Makindo Medical Notes

🛡️ Pattern Recognition Receptors (PRRs) are key components of innate immunity. They detect pathogen-associated molecular patterns (PAMPs) on microbes. This recognition triggers inflammation and antiviral defences, protecting the host from infection.

🧬 Types of Pattern Recognition Receptors (PRRs)

• 🛑 Toll-Like Receptors (TLRs) :
  • Found on cell surface & endosomes.
  • Detect bacterial LPS, viral RNA, fungal components.
  • ➡️ Trigger cytokines & type I interferons.
• ⚙️ NOD-Like Receptors (NLRs) :
  • Located in cytoplasm.
  • Detect bacterial peptidoglycan & DAMPs.
  • Form inflammasomes → activate caspase-1 → IL-1β & IL-18 release.
• 🧾 RIG-I-Like Receptors (RLRs) :
  • Cytoplasmic sensors of viral RNA.
  • Stimulate strong antiviral type I interferon response.
• 🍄 C-Type Lectin Receptors (CLRs) :
  • Surface receptors recognising fungal glucans & mannans.
  • Induce phagocytosis + inflammatory cytokines.
• 🧬 AIM2-Like Receptors (ALRs) :
  • Cytoplasmic sensors of double-stranded DNA.
  • Activate inflammasomes & pro-inflammatory cytokines.

⚙️ Mechanism of Action

• 🔎 Recognition: PRRs bind conserved microbial motifs (LPS, dsRNA, peptidoglycan).
• 📡 Signal Transduction: Activates NF-κB, MAPK, IRF → transcription of immune genes.
• 💥 Cytokine Production: Release of TNF-α, IL-1β, IL-6, IL-8 → recruit immune cells.
• 🌉 Adaptive Immunity: Antigen presentation enhanced → primes T-cell responses.

🛡️ Role in Immune Response

• ⏱️ Early detection: Rapid recognition of invading microbes.
• 🔥 Inflammation: Cytokines ↑ vascular permeability & immune recruitment.
• 🦠 Antiviral defence: RLRs induce interferons → block viral replication.
• ♻️ Pathogen clearance: PRR activation boosts phagocytosis & killing.

⚠️ Clinical Relevance

• 🦠 Infectious Disease: Defective PRRs → ↑ infection risk.
• 🔁 Autoimmunity: Overactivation → excessive inflammation (e.g., lupus, IBD).
• 💊 Therapeutics: PRRs are targets for vaccines & immune-modulating drugs.

📚 Summary

PRRs are the body’s early warning system. They sense microbial PAMPs and initiate signalling cascades that trigger cytokine release, inflammation, and activation of adaptive immunity. They are vital for host defence but can contribute to autoimmunity when dysregulated.