Understanding Cytokines

• Cytokines are proteins that facilitate communication between cells in the body.

Cytokine Function

• Regulate the development of immune effector cells.
• Direct the function of effector cells.
• Bind specific receptors on target cells.
• Trigger signal transduction pathways.
• Lead to gene expression and specific effector functions.

Patterns of Cytokine Secretion

• Autocrine: Cytokines bind to receptors on the same cell that secreted them.
• Paracrine: Cytokines bind to receptors on target cells in proximity.
• Endocrine: Cytokines bind to target cells in distant parts of the body.

Cytokine Attributes

• Iliotropy: Cytokines have different biological effects on different target cells.
• Redundancy: Two or more cytokines mediate similar functions.
• Synergism: The combined effect of two cytokines is greater than their individual effects.
• Antagonism: One cytokine inhibits or offsets the effects of another cytokine.
• Cascade Induction: One cytokine induces a cell to produce more cytokines, leading to cytokine production by other cells.

Cytokine Families

• Interleukin (IL) Family
• Interferon (IFN) Family
• Chemokine Family
• Tumor Necrosis Factor (TNF) Family

Cytokine Signaling

• Cytokines function as the hormones of the immune system and are secreted to communicate with other cells.
• Cytokines bind to receptors and trigger a response in the receiving cell, often promoting activation and proliferation of immune cells.
• Can increase body temperature, causing a fever.

Cytokine Action

• Autocrine: The cell producing the cytokine also responds to it.
• Paracrine: A cytokine produced by one cell affects nearby cells.
• Endocrine: A cytokine affects a cell that is far away, potentially in a different organ.

Cytokine Types

• Interleukins (IL): Named in order of discovery and act on both leukocytes and non-leukocytes.
• Tumor Necrosis Factors (TNFs): Can bind to tumor cell receptors and cause cell death and heavily involved in inflammatory responses.
• Interferons: Interfere with processes like viral replication.
• Type I: Produced by virally infected cells and induce antiviral protection in surrounding cells.
• Type II: Activates macrophages and CD4+ helper T cells.
• Colony Stimulating Factors: Bind to hematopoietic stem cells to promote proliferation and differentiation.
• Transforming Growth Factors: Inhibit proliferation and differentiation of various cells.
• Transforming Growth Factor Beta: Helps develop regulatory T cells that slow down or stop immune responses.

Cytokine Description Categorization

• Hematopoietic family (interleukin): Regulate immune cell development, hematopoiesis, and immune function.
• Interferon: These cytokines are involved in antiviral defense, immune regulation, and activation of natural killer cells
• Direct the migration of immune cells to infection, inflammation, or injury sites.
• Tumor necrosis (TNFs): Mediate inflammation, apoptosis, and cellular proliferation.

Examples of Cytokines

• IL-2: Stimulates T cell proliferation and activation.
• IL-4: Promotes Th2 cell differentiation and B cell class switching to IgE.
• IL-6: Mediates acute-phase responses and inflammation.
• IL-10: Has anti-inflammatory properties and inhibits immune responses, acting as a master regulator.
• IL-1α and IL-1β: Proinflammatory cytokines that induce fever and inflammation.
• IL-17A: Induces inflammation and recruits neutrophils.
• IL-15: Stimulates T cell and NK cell proliferation.
• IL-13: Functions similarly to IL-4 and is involved in allergy and asthma.
• IL-5: Promotes eosinophil production and function.
• IL-9: Involved in allergic responses and immune regulation.
• TNF-α: Induces inflammation, apoptosis, and fever.
• TNF-β (Lymphotoxin-α): Regulates immune responses and lymphoid tissue development.
• Granulocyte-Macrophage CSF (GM-CSF): Stimulates granulocyte and macrophage production.
• Macrophage CSF (M-CSF): Promotes macrophage differentiation.
• TGF-β1: Regulates immune responses, tissue repair, and fibrosis.
• IFN-α and IFN-β: Exhibit antiviral activity and enhance MHC expression.
• IFN-γ: Activates macrophages and enhances Th1 responses.
• CXCL8 (IL-8): Chemotactic for neutrophils.
• CCL2 (MCP-1): Attracts monocytes.
• CXCL10 (IP-10): Induces T cell migration.