Immunology Quiz on Leukocyte Recruitment

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Questions and Answers

What mediates the firm attachment of leukocytes to the endothelium during recruitment?

Integrins (correct)

Cytokines

Chemokines

Selectins

Which of the following cytokines is known to increase the avidity of integrins for their ligands?

TNF (correct)

IL-6

IFN-γ

IL-10

During phagocytosis, what is the first step that occurs?

Formation of a phagocytic vacuole

Engulfment

Recognition and attachment of the particle (correct)

Killing of the microbe

Which receptor specifically recognizes microbial sugars rather than host cell components?

Mannose receptors Signup and view all the answers

Which cells primarily predominate the early inflammatory infiltrate during immune response?

Neutrophils Signup and view all the answers

What process allows selected circulating proteins to enter the site of infection or tissue damage?

Increased permeability Signup and view all the answers

Which cells are primarily responsible for the ingestion and destruction of microbes in tissues?

Leukocytes Signup and view all the answers

What characterizes the endothelium lining blood vessels during an inflammatory response?

Circulating leukocytes adhere and migrate into tissues. Signup and view all the answers

Which of the following is a potential harmful consequence of inflammation?

Tissue damage and associated symptoms Signup and view all the answers

What typically happens to harmful consequences of inflammation over time?

They are self-limited and resolve as inflammation abates. Signup and view all the answers

What role do cytokines and growth factors play in the inflammatory response?

They facilitate recruitment and activation of immune cells. Signup and view all the answers

Which substances contribute to the extracellular matrix during an inflammatory reaction?

Extracellular matrix proteins and cells Signup and view all the answers

What does the presence of streaks indicating lymphangitis signify?

Inflamed lymphatic channels Signup and view all the answers

Which mediator is primarily responsible for inducing vasodilation in acute inflammation?

Histamine Signup and view all the answers

What is one consequence of increased vascular permeability during inflammation?

Fluid leak resulting in edema Signup and view all the answers

What condition may accompany lymphangitis, indicating further inflammation?

Lymphadenitis Signup and view all the answers

What role do leukocytes play in the context of increased vascular permeability?

Induce gaps between endothelial cells Signup and view all the answers

Which of the following is not a function of lymphatic vessels during inflammation?

Increasing blood flow to tissues Signup and view all the answers

What results from the leak of plasma proteins due to increased vascular permeability?

Formation of edema Signup and view all the answers

What is a major factor contributing to increased vascular permeability in acute inflammation?

Direct endothelial cell injury Signup and view all the answers

Which chemical mediator is specifically mentioned as causing gaps between endothelial cells?

Histamine Signup and view all the answers

What role do adhesion molecules play in leukocyte migration?

They facilitate slow rolling of leukocytes along the endothelium. Signup and view all the answers

Which integrin state is associated with stable adhesion of leukocytes?

High-affinity state Signup and view all the answers

What signals lead to the activation of integrins in leukocytes?

A combination of cytokines and chemokines Signup and view all the answers

Which molecules are necessary for the rolling phase of leukocyte migration?

P-selectin and E-selectin Signup and view all the answers

Which component of the extracellular matrix is mentioned in relation to macrophages and microbes?

Fibrin and fibronectin Signup and view all the answers

What is the primary function of PECAM-1 (CD31) in leukocyte migration?

Facilitates transmigration through the endothelium. Signup and view all the answers

Leukocytes sense signals during migration primarily through which types of molecules?

Adhesion molecules and chemokines Signup and view all the answers

What happens to integrins during the activation phase of leukocyte migration?

They switch from a low-affinity to a high-affinity state. Signup and view all the answers

What is the primary outcome of the leukocyte migration process described?

Leukocytes translocate to areas of injury or infection. Signup and view all the answers

The initial rolling of leukocytes is primarily characterized by what type of interaction?

Transient interactions mediated by low-affinity adhesion Signup and view all the answers

What is the primary role of actin polymerization in leukocyte migration?

To organize the cytoskeleton for effective cell movement Signup and view all the answers

In acute inflammation, which leukocyte type predominates in the initial response within the first 6 to 24 hours?

Neutrophils Signup and view all the answers

What is a consequence of using antagonists of leukocyte integrins in treatment?

Control of inflammation but reduced microbial defense Signup and view all the answers

Which cell type is often the first to arrive in response to viral infections?

Lymphocytes Signup and view all the answers

What triggers the initial attachment of neutrophils to endothelial cells during inflammation?

Adhesion molecules like P-selectin and E-selectin Signup and view all the answers

In allergic reactions, which type of leukocyte is primarily involved?

Eosinophils Signup and view all the answers

How does the infiltration of leukocytes change during the inflammatory response?

The type of leukocyte varies based on pathogen type Signup and view all the answers

What is the main effect of chemoattractants in the inflammatory response?

They promote the migration of leukocytes towards the site of inflammation Signup and view all the answers

Which of the following statements about the recruitment of leukocytes is correct?

Various leukocytes can be recruited depending on the stimulus Signup and view all the answers

In what way does the presence of activated lymphocytes, macrophages, and plasma cells reflect the immune response?

They demonstrate a profound response to specific pathogens Signup and view all the answers

Study Notes

Overview of Inflammation: Definitions and General Features

Inflammation is a vascularized tissue response that delivers leukocytes and host defense molecules to sites of infection or cell damage to eliminate the threat.
Inflammation is a protective response essential for survival.
Inflammation involves phagocytic leukocytes, antibodies, and complement proteins.
Inflammation normally resides in the blood, capable of rapid recruitment to any body site.
Inflammation includes processes that deliver cells and proteins into tissues, activating recruited cells/proteins to eliminate harmful substances.
The suffix "-itis" signifies inflammation in a specific organ (e.g., appendicitis, conjunctivitis).
The inflammatory reaction follows a series of steps.

Historical Highlights

Clinical observations of inflammation date back to 3000 BCE (Egyptian papyrus).
Celsus (1st century AD) identified the four cardinal signs of acute inflammation: redness, swelling, heat, and pain.
John Hunter (1793) recognized inflammation as a body response, not a disease.
Elie Metchnikoff (1880s) discovered phagocytosis.
Thomas Lewis emphasized the role of chemical mediators of inflammation.

Causes of Inflammation

Infections (bacterial, viral, fungal, parasitic) and microbial toxins are the most common causes.
Tissue necrosis from ischemia, trauma, physical/chemical injury triggers inflammation.
Foreign bodies/endogenous substances (urate crystals, etc.) can trigger inflammation.
Immune reactions (hypersensitivity) can cause inflammation and tissue damage.

Recognition of Microbes and Damaged Cells

Sentinel cells (e.g., macrophages) recognize microbial components and damaged cell products triggering an inflammatory response.
TLRs and other cellular receptors sense foreign invaders.
Damage-sensing sensors (e.g., NLRs) recognize molecules from damaged cells initiating inflammasome activation and IL-1 production, resulting in inflammation.

Acute Inflammation

Characterized by:
- Dilation of blood vessels increasing blood flow
- Increased microvasculature permeability allowing plasma proteins and leukocytes to leave the blood
- Leukocyte emigration, accumulation at the site of injury, and their activation to eliminate the offending agent
The vascular reactions involve changes in blood flow and permeability maximizing the movement of plasma proteins/leukocytes to the site of injury.
Exudate (high protein, cellular debris) differs from a transudate (low protein).

Increased Vascular Permeability

Histamine, bradykinin, leukotrienes constrict endothelial cells creating gaps in venules, allowing fluid and proteins to escape.
Endothelial injury leads to endothelial cell necrosis and detachment.

Leukocyte Recruitment to Sites of Inflammation

Margination. Red blood cells move to center of blood vessels causing white blood cells (leukocytes) to move to the outer edges of blood vessel.
Rolling. Leukocytes loosely attach and roll along endothelial walls via selectin molecules.
Stable adhesion. Rolling is followed by firm adhesion via integrin molecules.
Migration through endothelium. Leukocytes migrate through the endothelium via gaps between endothelial cells.

Chemotaxis of Leukocytes

Chemotaxis is the movement of cells along a chemical gradient.
Exogenous or endogenous substances act as chemoattractants (microbial products, cytokines).
Macrophages, neutrophils predominate in the first 6-24 hours, replaced by monocytes later.

Phagocytosis and Clearance of Offending Agents

Phagocytosis. Recognition and attachment of particle to be ingested leading to engulfment and the formation of a phagocytic vacuole and subsequent killing and degradation.
Phagocytes. Neutrophils and macrophages.
Phagocytic receptors (e.g., mannose), receptors for opsonins (IgG antibodies, C3b).
Intracellular destruction. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are formed inside phagocytic vacuoles, as well as lysosomal enzymes.

Mediators of Inflammation

Many substances (vasoactive amines, lipid mediators, cytokines, complement system products) initiate/regulate inflammatory reactions.
Sources of mediators include macrophages, dendritic cells, mast cells.
These mediators have overlapping actions.
Mediators are short-lived, thus regulation mechanisms exist.

Systemic Effects of Inflammation

Fever.
Acute-phase proteins.
Leukocytosis.
Septic shock (severe infection).

Morphological Patterns of Acute Inflammation

Serous inflammation. Leaking of cell-poor fluid into spaces caused by injury or body cavities.
Fibrinous inflammation. Increased vascular leakage causing leakage of larger molecules like fibrinogen leading to fibrinous exudate.
Purulent (suppurative) inflammation & Abscess. Production of pus (neutrophils, liquefied debris).

Chronic Inflammation

Prolonged, weeks-months.
Causes: persistent infection, hypersensitivity, prolonged exposure to toxic agents.
Characterized by mononuclear cell infiltration, tissue destruction, attempts at healing (angiogenesis, fibrosis).
Granulomatous inflammation. (Formation of granulomas, e.g., in tuberculosis, Crohn's disease).

Cells and Mediators of Chronic Inflammation

Macrophages: Dominant cells that secrete cytokines/growth factors.
Lymphocytes: Amplify inflammatory reactions by activating more macrophages via cytokine signaling.
Other cells: eosinophils, mast cells.

Tissue Repair

Regeneration of cells/tissues to normal states.
Connective tissue deposition (scar formation).
Steps in scar formation: Inflammation, cell proliferation (angiogenesis, fibroblast proliferation), connective tissue deposition (Collagen).

Healing of Skin Wounds

Healing by primary intention (clean incision): epithelial regeneration (migration, mitosis), granulation tissue filling.
Healing by secondary intention (large wound): more inflammation, exudate and debris, more granulation tissue, contraction.

Factors that Influence Tissue Repair

Infection.
Diabetes.
Nutrition.
Glucocorticoids.
Poor perfusion.
Foreign bodies.

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Description

Test your knowledge on the processes involved in leukocyte recruitment and the role of cytokines in immune responses. This quiz covers topics such as phagocytosis, receptor recognition, and the early cellular response during inflammation. Perfect for students studying immunology and related fields.