Innate and Adaptive Immunity

🧾 Innate Immunity – Key Points

  • Definition: A non-specific host defense mechanism that acts without producing antibodies.

  • Origin: Inborn or genetically acquired.

  • Speed: Acts quickly (minutes to hours).

  • Activation: Triggered by pattern recognition receptors (e.g., Toll-like receptors – TLRs) on immune cells.

  • Recognition: These receptors recognize Pathogen-Associated Molecular Patterns (PAMPs) – structures commonly found in pathogens.

✅ Examples of PAMPs:

  • LPS (lipopolysaccharide) – outer membrane of gram-negative bacteria

  • Flagellin – protein in bacterial flagella

  • Peptidoglycan – cell wall of gram-positive bacteria

  • Bacterial DNA

  • Viral DNA and RNA

🔄 Flowchart: Innate Immunity Activation

Pathogen enters body
        ↓
PAMPs on pathogen recognized by → TLRs on defensive cells
        ↓
TLRs bind to PAMPs
        ↓
Activation of innate immune response
        ↓
Initiation of defense mechanisms:
- Inflammation
- Phagocytosis (by macrophages, neutrophils)
- Cytokine release
        ↓
Pathogen elimination or containment

🧬 Innate vs Adaptive Immunity

Feature

Innate Immunity

Adaptive Immunity

Definition

First line of defense, non-specific

Second line of defense, highly specific

Onset (Speed)

Immediate (minutes to hours)

Delayed (days to weeks)

Specificity

Non-specific (same response to all pathogens)

Specific to each pathogen

Memory

No memory

Has memory (stronger and faster upon re-exposure)

Cells Involved

Neutrophils, macrophages, NK cells, dendritic cells

B cells, T cells (Helper & Cytotoxic)

Receptors Used

Toll-like Receptors (TLRs)

Antigen-specific receptors (BCRs & TCRs)

Examples

Skin, mucous membranes, fever, inflammation

Antibodies, memory cells, vaccine response

🧠 Summary:

  • Innate immunity is the body’s immediate and non-specific defense against pathogens.

  • Adaptive immunity is a delayed, specific immune response that involves B cells and T cells and leads to immunological memory.