Cytokines Overview and Functions

Cytokines

• Cytokines are soluble peptides secreted by various cells, mainly immune cells, but also others.
• They act as chemical messengers, binding to receptors on target cells to trigger biological responses.
• Cytokines cannot cross cell lipid membranes, hence they bind to specific receptors on the surface of the target cell.
• Cytokines mediate cross-talk between immune cells and other body systems like the nervous system.
• They play roles in both healthy individuals (e.g., hematopoiesis, immunity, inflammation) and disease (acute and chronic, including autoimmune diseases and cancer).

Actions and Attributes of Cytokines

• Autocrine: Cytokine acts on the cell that secreted it (e.g., IL-2 on T cells).
• Paracrine: Cytokine acts on nearby cells (e.g., IL-2 and IL-4 between immune cells).
• Endocrine: Cytokine acts systemically on distant cells (e.g., multiple inflammatory cytokines and effects on the CNS).

Actions and Attributes of Cytokines (continued)

• Pleiotropy: One cytokine can influence multiple seemingly unrelated phenotypic traits.
• Redundancy: Two or more cytokines can have a similar effect.
• Synergism: Cooperative effects of multiple cytokines.
• Antagonism: One cytokine can inhibit the effects of another.
• Cascade induction: One cytokine's action on a target cell can induce that cell to produce other cytokines, creating a cytokine storm.

Cytokine Families

• Interleukins (ILs): Originally produced by leukocytes, important in various immune functions. Examples include IL-1, IL-2, IL-4, IL-5, IL-6, IL-10.
• Hematopoietin superfamily: Stimulates blood cell development and differentiation.
• Interferons (IFNs): Interferes with viral replication. Two main types: Type 1 (IFN-α and IFN-β) and Type 2 (IFN-γ).
• Tumor necrosis factor (TNF): Highly pleomorphic, impacting inflammation and playing roles in both pro- and anti-inflammatory signaling.
• Chemokines: Small proteins that guide leukocytes to inflamed tissues. Example includes IL-8.
• Transforming Growth Factor-Beta (TGF-β): Involved in cell growth and differentiation.
• Adipokines: Produced by fat tissue (adipocytes), impacting inflammation, metabolism.
• Colony-stimulating factors (CSFs): Stimulate the production of blood cells.
• Nerve growth factors: Stimulate nerve cell growth and survival.
• Angiogenic factors: Promote blood vessel growth.

Cytokine Receptor Families

• Type I: Cytokine receptors like IL-2 receptor have common motifs in their extracellular regions and structural components.
• Type II: Binding sites for interferons.
• TNF Receptors: Bind TNF and other ligands leading to cell death pathways.
• IL-1 Receptors: Binding sites for IL-1 triggering signaling.
• Chemokine receptors: Primarily G-protein-coupled receptors (GPCRs) for recognition and binding of chemokines.

Roles of Cytokines

• Cytokines play key roles in inflammation and are involved in septic shock, influencing local and systemic responses to infection.

• Pro-inflammatory cytokines, secreted by activated macrophages, have local and systemic impacts, such as fever and vascular leakage.

• Sepsis: Systemic inflammation driven by an overactivated immune response to infection, causing tissue damage, and eventually potentially death.

• Cytokine storms: An uncontrolled release of cytokines, contributing to severe inflammation in various diseases, such as COVID-19.

Explore the fascinating world of cytokines, which serve as essential chemical messengers in the immune system and beyond. This quiz covers their roles, actions, and the mechanisms through which they influence both health and disease. Test your understanding of the autocrine, paracrine, and endocrine functions of these vital peptides.