Cytokines and Their Regulation – Lecture Review

These question-and-answer flashcards review the key definitions, mechanisms, receptor types, signalling pathways, and functional roles of cytokines described in Dr. Shihabuddin’s lecture on Cytokines and Regulations.

Approximately what is the molecular weight of most cytokines?

Around 30 kDa (low-molecular-weight proteins).

What is the major role of cytokines in the immune system?

They act as soluble messengers for cell-to-cell communication, directing magnitude and outcome of immune responses.

When a cytokine acts on the same cell that secreted it, what type of action is this?

Autocrine action.

What type of cytokine action targets nearby cells?

Paracrine action.

What term describes hormone-like systemic cytokine activity?

Endocrine action.

Which cytokine family is specialized for chemotaxis of leukocytes?

Chemokines.

Give one example of a chemokine.

Interleukin-8 (IL-8).

What word describes a single cytokine that produces different effects on different target cells?

Pleiotropy.

What is cytokine ‘redundancy’?

Two or more cytokines produce the same or very similar biological effect.

Define cytokine ‘synergy’.

The combined effect of two cytokines exceeds the sum of their individual effects.

What is meant by ‘cascade induction’ in cytokine biology?

A cytokine stimulates a target cell to produce additional cytokines, creating a chain reaction.

Name three classic pro-inflammatory cytokines involved in acute inflammation.

IL-1, IL-6 and TNF-α.

Which cytokines act as endogenous pyrogens to induce fever?

IL-1, IL-6 and TNF-α.

Which cytokines trigger hepatocytes to produce acute-phase proteins?

IL-1, IL-6, TNF-α (also LIF and Oncostatin M).

What acute-phase protein can rise 1000-fold during inflammation?

C-reactive protein (CRP).

Which cytokine is key for class switching to IgE?

IL-4.

Which cytokine strongly activates macrophages and promotes antiviral responses?

Interferon-γ (IFN-γ).

List any three of the five major cytokine receptor families.

Hemopoietin (Class I), Interferon (Class II), TNF receptor family (others: Immunoglobulin superfamily, Chemokine receptors).

Which conserved motif characterizes most Class I cytokine receptors?

The WSXWS motif in the extracellular domain.

Which intracellular signalling pathway is mainly used by Class I and II cytokine receptors?

The JAK-STAT signalling pathway.

Name the four members of the Janus kinase (JAK) family.

JAK1, JAK2, JAK3 and Tyk2.

Where are STAT proteins located before activation?

Latent in the cytosol.

Mutation of which JAK isoform can cause severe combined immune deficiency (SCID)?

JAK3.

What is a cytokine receptor antagonist?

A molecule that binds a cytokine receptor (or the cytokine itself) without triggering signalling, thereby blocking activity.

Give a specific example of a cytokine receptor antagonist.

IL-1 receptor antagonist (IL-1Ra).

Into what three functional groups are cytokines commonly classified?

Mediators of innate immunity, mediators of adaptive immunity, stimulators of haemopoiesis.

Give two examples of cytokines that mediate innate immunity.

TNF-α and IFN-α/β (others: IL-1, IL-6, IL-10, IL-12, IL-15, chemokines).

Give two examples of cytokines that mediate adaptive immunity.

IL-2 and IL-4 (others: IFN-γ, lymphotoxin).

Which cytokine drives proliferation of antigen-primed T cells?

Interleukin-2 (IL-2).

Which cytokine induces stromal cells and macrophages to release colony-stimulating factors during tissue repair?

TNF-α.

What cell types are the principal producers of chemokines?

Macrophages and dendritic cells (along with other leukocytes).

What immediate change happens to a cytokine receptor when its ligand binds?

Receptor dimerization or polymerization leading to intracellular signalling.

Cytokine–receptor interactions exhibit very high affinity. What dissociation constant (Kd) range is typical?

10⁻¹⁰ to 10⁻¹⁵ M (picomolar range).

After phosphorylation, where does a STAT dimer migrate?

Into the nucleus to bind DNA and drive gene expression.

Name three adhesion molecules up-regulated by IL-1 and TNF on vascular endothelium.

E-selectin (ELAM-1), ICAM-1 and VCAM-1.

What is the key purpose of a chemokine concentration gradient?

To guide leukocyte migration (chemotaxis) toward sites of infection or injury.

Which group of cytokines directly interferes with viral replication?

Type I interferons (IFN-α and IFN-β).

Which cytokine limits inflammation and promotes fibroblast-mediated tissue repair?

Transforming growth factor-β (TGF-β).

How do some viruses subvert cytokine-mediated immunity?

They produce cytokine mimics or soluble cytokine-binding proteins (e.g., poxvirus IL-1-binding protein).

Which macrophage-derived cytokine is antitumour yet contributes to cachexia in chronic inflammation?

Tumour necrosis factor-α (TNF-α).

List all five major cytokine receptor families.

Class I (Hemopoietin), Class II (Interferon), TNF receptor superfamily, Immunoglobulin superfamily, Chemokine receptor family.

What structural feature defines chemokine receptors?

Seven transmembrane, G-protein-coupled (serpentine) structure.

IL-2 and IL-15 share what unique receptor characteristic?

Their high-affinity receptors are trimeric (α, β and γ chains).

What is the primary action of interleukin-5 (IL-5)?

Stimulates eosinophil development/activation and promotes B-cell IgA class switching.

In cytokine terminology, what is an ‘additive’ effect?

The combined effect of two cytokines equals the sum of their separate effects (no synergy).