Chapter 2 - Innate Immune Responses (Part I)

What are Pattern Recognition Receptors (PRRs)?

Proteins that recognize Pathogen-Associated Molecular Patterns (PAMPs) and help the innate immune system distinguish between "dangerous" and "innocuous" things.

List three important features of PAMPs.

• Not produced by the host organism.

• Shared by large groups of pathogens.

• Essential for pathogen survival.

What are two examples of PAMPs?

Peptidoglycan in Gram-positive bacteria and lipopolysaccharide (LPS) in Gram-negative bacteria. Double-stranded RNA or single-stranded DNA in viruses

What are the two main groups of cell-associated membrane PRRs?

Phagocytosis receptors and Toll-like Receptors (TLRs).

What is the role of Toll receptors in Drosophila?

They bind infectious organisms and release anti-fungal or anti-microbial peptides.

How do mammalian TLRs resemble Drosophila Toll? ie their structure

They have leucine-rich domains for PAMP recognition, transmembrane domains, and cytoplasmic domains homologous to IL-1 receptors.

How many functional TLRs exist in humans?

11

What is the result of TLR activation in mammals?

Activation of NF-κB, leading to the production of antimicrobial peptides.

What is the complement system?

A set of plasma proteins that attack extracellular pathogens through a cascade of reactions.

How is the classical complement pathway activated?

By antibodies from a previous adaptive immune response binding to the pathogen surface.

What activates the alternative complement pathway?

Direct binding of complement proteins to the pathogen surface without the need for antibodies.

What is the function of C3 convertase in the complement cascade?

Cleaves C3 into C3a and C3b, initiating further reactions in the complement system.

What are the three major outcomes of the complement system?

• Activation of the inflammatory response.

• Opsonization and enhanced phagocytosis.

• Formation of the membrane attack complex (MAC) causing pathogen lysis.

What triggers inflammation in tissues?

Tissue damage and activation of mast cells, which release histamine.

How do C3a and C5a contribute to inflammation?

They increase blood vessel permeability, recruit leukocytes, and act as anaphylatoxins.

What is the role of C3b in phagocytosis?

Acts as an opsonin, enhancing the efficiency of pathogen engulfment by phagocytes.

What is the membrane attack complex (MAC)?

A structure formed by complement proteins that punches holes in a pathogen’s membrane, causing lysis.

How do dendritic cells link innate and adaptive immunity?

By activating T cells to initiate adaptive immune responses.

What is the role of the complement cascade?

It activates inflammation, promotes phagocytosis, and causes pathogen lysis.

How do PAMPs trigger the innate immune system?

They bind to PRRs, causing phagocytosis or cytokine production.

What is the primary function of the innate immune response?

Rapid, non-specific recognition and destruction of pathogens.