Innate Immunity and Pathogen Recognition

Innate Immunity: A First Line of Defense

• Innate immunity is the body's first and non-specific line of defense against pathogens.
• It is rapid and present from birth, acting immediately to eliminate invading pathogens.
• It doesn't have memory; responses are the same for repeated encounters.
• This approach relies on various mechanisms to recognize and eliminate pathogens.

Pathogen Recognition

• Pattern Recognition Receptors (PRRs) are crucial components of innate immunity.
• These receptors recognize pathogen-associated molecular patterns (PAMPs).
• PAMPs are conserved molecular structures found on various pathogens.
• PRRs include Toll-like receptors (TLRs), NOD-like receptors (NLRs), and RIG-I-like receptors (RLRs).
• Binding of PAMPs to PRRs triggers a cascade of intracellular signaling events.
• Other receptors include C-type lectin receptors (CLRs) and scavenger receptors.

Inflammatory Response

• Inflammation is a critical component of innate immunity, characterized by redness, swelling, heat, and pain.
• It is initiated by the recognition of pathogens and damaged tissues.
• Cytokines are key mediators of the inflammatory response.
• The inflammatory response involves the recruitment of immune cells to the site of infection or injury.
• Vasodilation and increased vascular permeability are crucial for the recruitment of immune cells and the delivery of inflammatory mediators.
• Pro-inflammatory cytokines (e.g., TNF-α, IL-1β) initiate and regulate inflammation, attracting neutrophils and macrophages.
• Resolution of inflammation is a tightly regulated process to prevent chronic inflammation leading to tissue damage

Antimicrobial Peptides

• Antimicrobial peptides (AMPs) are small, cationic peptides produced by a variety of cells.
• They contribute to innate immunity by directly killing or inhibiting the growth of pathogens.
• Mechanisms include membrane disruption, inhibiting enzymatic activity, or disrupting the cell wall of pathogens.
• Many AMPs are found in various mucosal surfaces.
• Examples of AMPs include defensins and cathelicidins.

Cytokine Signaling

• Cytokines are signaling molecules crucial for coordinating immune responses.
• They regulate the activation and differentiation of immune cells.
• Cytokine signaling often involves a cascade.
• Cytokine receptors on target cells bind specific cytokines, initiating intracellular signaling pathways that cause biological effects.
• Type I interferons (e.g., IFN-α, IFN-β) combat viral infections.
• Interleukins (ILs) mediate interactions between various immune cells.

Immune Cell Types

• Key immune cells involved in innate immunity include neutrophils, macrophages, dendritic cells, and natural killer (NK) cells.
• Neutrophils are phagocytic cells that rapidly migrate to sites of infection to engulf and destroy pathogens.
• Macrophages are antigen-presenting cells that engulf and destroy microbes; they also release cytokines involved in inflammation and immune regulation.
• Dendritic cells bridge innate and adaptive immunity. They capture and process antigens that are then presented to lymphocytes.
• Natural killer (NK) cells identify and eliminate virally infected or cancerous cells.
• These cells release cytotoxic granules to induce apoptosis in target cells.
• Mast cells are involved in allergic responses and inflammation.
• Eosinophils play a role in defence against certain pathogens, particularly parasites.

Explore the fundamentals of innate immunity, the body's first line of defense against pathogens. This quiz covers the mechanisms of pathogen recognition through Pattern Recognition Receptors (PRRs) and the role of inflammation in immune responses. Test your knowledge on how the body responds to threats without memory of past encounters.