Immunology: Toll-like Receptors and Phagocytosis

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Questions and Answers

What role do Toll-like receptors (TLRs) play in the immune system?

TLRs produce antibodies to fight infection.

TLRs are responsible for clotting blood.

TLRs help red blood cells transport oxygen.

TLRs recognize common structures on different microbes. (correct)

Which cell types are primarily involved in phagocytosis?

Natural killer cells and mast cells

Eosinophils and basophils

T cells and B cells

Neutrophils and macrophages (correct)

How many different Toll-like receptors are found in humans?

Five

Seven

Ten (correct)

Twelve

What are the stages of phagocytosis?

Recognition, ingestion, digestion Signup and view all the answers

Which scientist identified mammalian TLR4 as the LPS receptor?

Beutler Signup and view all the answers

Which characteristic describes innate immunity?

It is always present and functional. Signup and view all the answers

What is a primary function of complement in innate immunity?

To enhance phagocytosis and induce inflammation. Signup and view all the answers

Which type of cell is primarily responsible for phagocytosis in the innate immune system?

Macrophages Signup and view all the answers

What recognizes pathogen-associated molecular patterns (PAMPs) in innate immunity?

Pattern recognition receptors (PRRs) Signup and view all the answers

Which of the following components is involved in the internal defenses of innate immunity?

Phagocytosis Signup and view all the answers

Which statement about natural killer (NK) cells is correct?

NK cells directly kill virus-infected and tumor cells. Signup and view all the answers

What is the main role of tight junctions in epithelial cells in innate immunity?

To serve as a barrier to pathogen entry. Signup and view all the answers

Which feature of innate immunity distinguishes it from adaptive immunity?

It provides a quick response to pathogens. Signup and view all the answers

What is the primary function of complement as described in the content?

Opsonisation Signup and view all the answers

Which of the following mediators is NOT involved in inflammation according to the content?

C5b Signup and view all the answers

What is the central component of the complement system?

C3 Signup and view all the answers

Which pathway is mainly activated by immune complexes containing IgM or IgG?

Classical pathway Signup and view all the answers

What is a significant consequence of classical pathway deficiencies in complement?

Increased risk of autoimmune diseases Signup and view all the answers

What complex is formed in the classical pathway that leads to the conversion of C3?

C4b2a Signup and view all the answers

How does the Membrane Attack Complex (MAC) function within the immune response?

It disrupts fluid balance leading to pathogen lysis Signup and view all the answers

Which of the following components is NOT involved in the alternative pathway?

C1q Signup and view all the answers

Which complement component is primarily recognized by CR1 on phagocytes to enhance phagocytosis?

C3b Signup and view all the answers

How do plasma inhibitors affect the activation of the complement system?

They prevent activation in the absence of pathogens. Signup and view all the answers

What is the role of C3b in the complement system?

Opsonization Signup and view all the answers

Which of the following can activate the C1 complex in the classical pathway?

C reactive protein Signup and view all the answers

What triggers the series of inflammatory events in the complement system?

Activated C3 Signup and view all the answers

What is the primary function of Natural Killer (NK) cells?

To release perforin and granzyme to kill infected or cancerous cells Signup and view all the answers

What percentage of blood lymphocytes are comprised of Natural Killer cells?

10-15% Signup and view all the answers

How do innate immune cells distinguish 'self' from 'non-self' cells?

By using pattern recognition receptors that bind to PAMPs Signup and view all the answers

What is a characteristic of the innate immune response?

It is relatively non-specific and does not develop over time Signup and view all the answers

What role do Toll-like receptors play in the immune system?

They bind to pathogen-associated molecular patterns (PAMPs) Signup and view all the answers

Study Notes

Innate Immunity Lecture Notes

Learning Objectives:
- Characteristics of the innate immune system
- Pathogen recognition by innate immune cells
- Functions of the innate immune system (phagocytosis, complement, natural killer cells)

Innate Defenses

Physical Barriers:
- Tight junctions at epithelial cells
- Mucous membranes
- pH
- Antimicrobial secretions (e.g., lysozyme in tears)
Internal Defenses:
- Phagocytosis
- Complement
- Natural Killer Cells
- Cytokine secretion

Adaptive Defenses

Humoral Immunity:
- B cells
- Antibodies
Cell-Mediated Immunity:
- T cells
- Cell killing
- Cytokine secretion

Cells Involved in Innate and Adaptive Immunity

Innate Immunity (Hours):
- Basophils
- Eosinophils
- Neutrophils
- Macrophages
- Mast cells
- Natural killer cells
- Dendritic cells
Adaptive Immunity (Days):
- Antibodies
- B cells
- Cytokines
- Cytotoxic molecules
- T cells

Features of Innate/Natural Immunity

Innate immunity is present from birth and is always functional.
It can respond immediately to pathogens.
It instructs the adaptive immune system.
It recognizes non-self (foreign) structures in a non-specific way.
It has no memory of previous infections and cannot improve its response with experience.

Pathogen Recognition by Innate System Cells

Proposed by Janeway (1989).
Innate cells have pattern recognition receptors (PRRs).
PRRs are encoded in germline cells and have limited diversity.
Toll-like receptors (TLRs) and NOD-like receptors are examples of PRRs.
PRRs recognize pathogen-associated molecular patterns (PAMPs) -shared by different classes of microbes.
- Examples of PAMPs include peptidoglycan, lipopolysaccharide (LPS).

Innate Immune Recognition of Bacterial Cell Wall Components

Gram-negative bacteria: have lipopolysaccharide in outer membrane, porins.
Gram-positive bacteria: have teichoic acid and peptidoglycan.

Identical Toll-like Receptors

Recognize common structures on different microbes.

Complement

30 plasma proteins in an inactive state.
Become active at infection sites, triggering inflammatory events.
C3 is a central component in the complement cascade.
Three pathways activate complement:
- Classical pathway
- Alternative pathway
- Lectin pathway
A "membrane attack complex" (MAC) forms to lyse pathogens.

Classical Pathway Activation

Activated by immune complexes containing IgM or IgG.
Other activators include C-reactive protein, lipopolysaccharide, bacterial porins.

Safety Checks of Classical Pathway

Covalent binding of C4b and C3b to the activator ensures the reaction stays on the pathogen surface.
Plasma and host cell inhibitors prevent activation in the absence of a pathogen.

Membrane Attack Complex (MAC)

Disrupts fluid balance, leading to lysis of pathogens.
Composed of C5b, C6, C7, C8, and multiple C9 molecules.

Functions of Complement

Opsonization:
- C3b binds to complement receptor type I (CR1 or CD35) on phagocytes.
- C5a activates phagocytosis when C3b is bound to CR1.
Cell Lysis: Through the membrane attack complex.
Inflammation: C3a, C4a, and C5a are inflammatory mediators that activate cells.
Recruits adaptive immunity: Some components stimulate B-cell activation.

Deficiencies of Complement

Deficiency in the classical pathway (especially C1q) increases susceptibility to autoimmune diseases like SLE.
Can also increase susceptibility to some bacterial infections (e.g., Streptococcus pneumoniae, Haemophilus influenzae).

Natural Killer (NK) Cells

Lymphoid lineage (10-15% of blood lymphocytes).
Recognize if a cell has a viral infection or is cancerous.
Kill infected cells by releasing perforin.
Perforin creates holes in the target cell membrane.
Granzyme enters the target cell through the perforin pore
Induces apoptosis (programmed cell death).

Summary of Main Points

Innate immunity responds quickly but is non-specific.
Innate cells do not have memory.
Innate cells distinguish self from non-self using pattern recognition receptors (PRRs).
They bind to pathogen-associated molecular patterns (PAMPs).
Innate functions include phagocytosis, complement activation, NK cell killing.
Facilitate the killing of pathogens and activate the adaptive immune response.

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Description

This quiz explores the roles of Toll-like receptors (TLRs) and the process of phagocytosis within the immune system. It covers important concepts such as innate immunity, complement function, and key cell types involved in these processes. Test your knowledge on the fundamentals of immunology!