Citokinek

Citokinek are small secreted proteins that mediate communication between cells, particularly in the immune system. They are produced by various cells, including macrophages, dendritic cells, T and B lymphocytes, endothelial cells, and fibroblasts, often in response to infection, tissue damage, or other cytokines. After secretion, they act by binding to specific receptors on target cells, triggering signaling cascades that alter gene expression and cellular behavior.

Cytokines are functionally diverse and are commonly grouped into families such as interleukins, interferons, tumor necrosis factors, chemokines, and growth factors. They can be pro-inflammatory, anti-inflammatory, or immunoregulatory. Chemokines primarily regulate leukocyte trafficking, while interleukins coordinate activation and differentiation of lymphocytes. The same cytokine can have multiple effects depending on the cellular context and receptor expression.

Signaling and pathways: cytokine receptors often activate JAK-STAT, MAPK, and PI3K-AKT pathways. These signals regulate proliferation, migration, survival, and differentiation. Many cytokines exhibit pleiotropy and redundancy, meaning a single cytokine can influence several cell types and a single cell type can respond to multiple cytokines.

Physiological and clinical relevance: Cytokines are essential for innate and adaptive immunity, development, tissue repair, and metabolism. Dysregulated production is linked to autoimmune diseases, allergic reactions, infections, and cancer. Therapeutically, cytokines and their signaling pathways are targets for drugs, including monoclonal antibodies against TNF-α or IL-6, receptor antagonists, and JAK inhibitors.

Measurement and regulation: Cytokine levels are measured in blood and tissues for research and clinical purposes, though their transient nature can complicate interpretation. Regulatory mechanisms include soluble receptors, receptor antagonists, and feedback inhibitors such as SOCS proteins.