Innate Immunity Lecture Overview

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Questions and Answers

Which type of bacteria is recognized by Toll-like receptors in the innate immune response?

Only Gram-positive bacteria

Only Gram-negative bacteria

Neither Gram-negative nor Gram-positive bacteria

Both Gram-negative and Gram-positive bacteria (correct)

Which of the following cells are primarily involved in phagocytosis?

Eosinophils and basophils

B lymphocytes and dendritic cells

Natural killer cells and T lymphocytes

Neutrophils and macrophages (correct)

Which receptor was identified by Beutler as the LPS receptor in mammals?

TLR2

TLR8

TLR4 (correct)

TLR6

Which of the following processes is NOT involved in phagocytosis?

Replication Signup and view all the answers

How many different Toll-like receptors (TLRs) are present in humans?

10 Signup and view all the answers

What is the primary function of C3b in the complement system?

Opsonization for phagocytosis Signup and view all the answers

Which components are specifically known as mediators of inflammation?

C3a, C4a, and C5a Signup and view all the answers

A deficiency in which component is most closely associated with an increased risk of developing systemic lupus erythematosus (SLE)?

C1q Signup and view all the answers

What consequence does the Membrane Attack Complex (MAC) cause to pathogens?

Lysis of the pathogen Signup and view all the answers

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

To recognize and kill infected or cancerous cells Signup and view all the answers

Which of the following functions is NOT performed by components of the complement system?

Direct destruction of viral pathogens Signup and view all the answers

What mechanism do NK cells use to induce cell death?

Release of perforin and granzyme Signup and view all the answers

How does the innate immune system differentiate between self and non-self?

Using pattern recognition receptors Signup and view all the answers

Which feature of the innate immune system is true?

It is relatively non-specific Signup and view all the answers

Which of the following functions is NOT associated with innate immune mechanisms?

Activation of T cells and B cells Signup and view all the answers

What is a key characteristic of the innate immune system?

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

Which of the following correctly describes pathogen recognition in innate immunity?

It uses pattern recognition receptors (PRRs). Signup and view all the answers

Which function is NOT associated with the innate immune system?

Production of antibodies Signup and view all the answers

What role do antimicrobial secretions play in innate immunity?

They directly destroy microbes. Signup and view all the answers

What is the significance of pathogen-associated molecular patterns (PAMPs)?

They are recognized by pattern recognition receptors. Signup and view all the answers

Natural Killer (NK) cells are primarily involved in which aspect of innate immunity?

Cytotoxic activity against infected cells Signup and view all the answers

Which statement about the diversity of pattern recognition receptors (PRRs) is accurate?

PRRs are encoded in the germline with limited diversity. Signup and view all the answers

What distinguishes innate immunity from adaptive immunity?

Innate immunity is non-specific and immediate. Signup and view all the answers

Which plasma protein is central to the complement system?

C3 Signup and view all the answers

What is the role of C3a in the complement system?

Trigger inflammation 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 ensures that the reaction of the classical pathway stays on the surface of a pathogen?

Covalent binding of C4b and C3b Signup and view all the answers

Which components are involved in the formation of the C3 convertase in the classical pathway?

C2, C4, and C3b Signup and view all the answers

Which factor is associated with the alternative pathway of the complement system?

Properdin Signup and view all the answers

Activation of the classical pathway involves which of the following activators?

Lipopolysaccharide (LPS) Signup and view all the answers

What role does C4b play in the classical pathway?

Covalently binds to the activator Signup and view all the answers

Study Notes

Innate Immunity Lecture Notes

The lecture covers the characteristics of the innate immune system.
The innate system recognizes pathogens by innate cells.
The innate system has key functions, including phagocytosis and complement.
Natural killer (NK) cells are part of the innate system.
Physical barriers (e.g., tight junctions, mucous membranes, pH, antimicrobial secretions) are the first line of defense.
Internal defenses (e.g., phagocytosis, complement, natural killer cells, cytokine secretion) are the second line of defense.
The adaptive immune system is comprised of humoral and cell-mediated immunity.
Humoral immunity involves B cells and antibodies.
Cell-mediated immunity involves T cells, cell killing, and cytokine secretion.

Learning Objectives

Characteristics of the innate immune system branch.
Pathogen recognition by innate cells.
Innate system functions (e.g., phagocytosis, complement).
Natural killer (NK) cells.

Cells Involved in Innate and Adaptive Immunity

Innate immunity involves Basophils, Eosinophils, Neutrophils, Mast cells, Natural Killer cells, Macrophages, and Dendritic cells; acting in hours.
Adaptive immunity involves B cells, and T cells, acting in days.

Features of Innate/Natural Immunity

Innate immunity is present from birth and is always functional.
It can respond quickly.
It instructs the adaptive immune system.
Innate immunity recognizes non-self in a non-specific manner.
It lacks the ability to remember pathogens or improve with experience.

Pathogen Recognition by Innate System Cells

Innate cells use pattern recognition receptors (PRRs).
PRRs recognize pathogen-associated molecular patterns (PAMPs) which are structures shared by various microbes (e.g., peptidoglycan, lipopolysaccharide (LPS)).
PRRs, like Toll-like receptors (TLRs) and NOD-like receptors, are encoded in germline and have limited diversity.

Innate Immune Recognition of Bacterial Cell Wall Components

Gram-negative bacteria have a lipopolysaccharide (LPS) outer membrane and porins.
Gram-positive bacteria have a peptidoglycan layer and teichoic acids.

Identical Toll-like Receptors

Identical Toll-like receptors recognize common structures on diverse microbes.

TLRs (Toll-like Receptors)

Jules Hoffman discovered that Toll receptors (in Drosophila) are crucial for immune defense.
Beutler determined mammalian TLR4 (an LPS receptor).
TLRs are critical for innate immune defense.
Humans have 10 different TLRs.
TLRs are expressed by various cells (e.g., macrophages, dendritic cells).
TLRs are found on cell surfaces and intracellular vesicles.

Phagocytosis

Neutrophils and macrophages are important phagocytes.
Following infection, these cells travel to infection sites.
Phagocytosis involves recognition, ingestion, and digestion.
Phagocytes surround and engulf pathogens.
Lysosomes fuse with phagosomes to digest pathogens.
The process involves chemotaxis, adherence, ingestion in phagosomes, fusion with lysosomes, digestion, and waste disposal.

Complement

Thirty plasma proteins normally circulate in an inactive state.
Activation occurs at infection sites, triggering inflammatory events.
C3 is a pivotal component of the complement system.
Complement activation involves three pathways (classical, alternative, lectin).
The classical pathway is activated by antibodies.
The alternative pathway is activated by microbial components.
The lectin pathway is triggered by mannose-binding lectin (MBL).
The complement system causes cell lysis (via MAC), inflammation, and opsonization.

Classical Pathway Activation

Activators include immune complexes (containing IgM or IgG), C-reactive protein, lipopolysaccharide (LPS), bacterial porins, and others.

Classical Pathway (Safety Checks)

Covalent binding of C4b and C3b to the activator ensures the reaction stays on the pathogen's surface.
Inhibitors in plasma and on host cells prevent activation in the absence of a pathogen.

Membrane Attack Complex (MAC)

The MAC creates pores in the pathogen membrane, leading to lysis.
MAC components (C5, C6, C7, C8, and C9) assemble to form the MAC.
This results in pathogen lysis or death.

Functions of Complement (Opsonization)

C3b is recognized by complement receptor type 1 (CR1 or CD35) on phagocytes.
C5a can activate phagocytosis where C3b is attached to CR1.
Opsonization is a crucial function of complement.

Functions of Complement (Cell Lysis, Inflammation, Recruitment, Adaptive Immunity Stimulation)

Membrane attack complex (MAC) causes cell lysis.
C3a, C4a, and C5a are inflammatory mediators.
Complement components can stimulate B-cell activation and antibody production.

Complement Deficiencies

Deficiencies in the classical pathway increase susceptibility to autoimmune diseases (especially SLE) and bacterial infections (e.g., Streptococcus pneumoniae, Haemophilus influenzae).

Natural Killer (NK) Cells

NK cells are a type of lymphoid cell (10–15% of blood lymphocytes).
NK cells identify virus-infected or cancerous cells.
These cells have altered surface structures.
NK cells lyse target cells via perforin (creating pores) and granzyme (inducing apoptosis).

Summary of Main Points

The innate immune system responds rapidly and is relatively non-specific.
It does not develop memory.
Innate cells differentiate self from non-self via pattern recognition receptors.
Innate functions include phagocytosis, complement activation, and direct killing by NK cells.
These functions allow innate immunity to kill pathogens and virally/cancerously infected host cells.
Innate mechanisms trigger and initiate the adaptive immune response.

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Description

This quiz explores the fundamental aspects of the innate immune system, including its characteristics, functions, and key components. It covers how innate cells recognize pathogens and the role of natural killer cells. Understand the first and second lines of defense in the immune response.