Immunity - Innate adaptive immunity

Define the term immunity

Naturally existing mechanisms which defend the organism from external and internal agents and maintain its immunological homeostasis.

What are pathogen-associated molecular patterns (PAMPs), and how do they activate the innate immune response?

1.  PAMPs are molecular structures found in pathogens but not in humans (e.g., lipopolysaccharide, flagellin, RNA/DNA). They bind to pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs), on innate immune cells (e.g., macrophages, dendritic cells). This triggers signaling cascades that activate NF-κB, leading to cytokine production, inflammation, and upregulation of adhesion molecules.

1. List three outcomes of NF-κB activation in the innate immune system.

• Cytokine production (e.g., IL-1, TNF-α)

• Inflammation

• Upregulation of endothelial adhesion molecules

Definition of TLR toll like receptors

1. Toll like receptors are LLR containing proteins that function as pattern recognition receptors (PRR’s). Some TLR are present on the cell surface to recognize extracellular microbe products, and others are endosomed into which microbes are ingested. Upon activation, TLR’s trigger NF-kB, leading to the expression of cytokines and endothelial adhesion molecules, initiating antimicrobial and inflammatory response. 

Features of innate immunity:

• Non-specificity - responds to a broad range of pathogens, without targeting a specific antigen. 

• Recognition - recognizes pathogen-associated molecular patterns (PAMPs) using pattern recognition receptors (PRPs), like toll-like receptors (TLRs.)

• PAMPs - found in pathogens not humans, examples include; lipopolysaccharide (LPs), flagellin, RNA/DNA. Binds to pattern recognition receptors (PRRs) on innate immune cells (e.g., macrophages, dendritic cells). Triggers signalling cascades that activate NF-kB leading to:

   

  • Cytokine production (e.g., IL-1, TNF- alpha)

  • Inflammation 

  • Upregulation of adhesion molecules 

Actions of Innate immunity include:

1. Phagocytosis - Neutrophils, macrophages and dendritic cells engulf and destroy pathogens using hydrolytic enzymes (lysozyme, proteases, nucleases and lipases). They also present antigens to the adaptive immune system.

2. Cytokine production - Innate cells release proinflammatory cytokines and chemokines to coordinate the immune response. 

3. Nk-cell activity - NK are cytotoxic, their cytoplasm contain perforin and granzymes.

   Upon release in close proximity to a cell slated for killing, perforin forms pores in the cell membrane of the target cell through which the granzymes and associated molecules can enter, inducing apoptosis. Nk-cells are activated in response to interferons or macrophage-derived cytokines.

Definition

Phagocytosis - Phagocytosis is the cellular process of engulfing solid particles by the cell membrane to form an internal phagosome.