Clinical meaning
Cytokine signaling involves binding of extracellular cytokines to specific membrane receptors, triggering intracellular signal transduction cascades that alter gene expression. The JAK-STAT pathway is the primary signaling mechanism for Type I and II cytokine receptors: cytokine binding activates receptor-associated Janus kinases (JAK1, JAK2, JAK3, TYK2), which phosphorylate STAT proteins; phosphorylated STATs dimerize, translocate to the nucleus, and activate target gene transcription (immune cell differentiation, proliferation, survival). The NF-κB pathway mediates TNF-alpha, IL-1, and TLR signaling: activating IKK which phosphorylates IκB, releasing NF-κB to translocate to the nucleus and activate pro-inflammatory gene transcription. These pathways are now therapeutic targets: JAK inhibitors (tofacitinib, baricitinib, ruxolitinib) and anti-TNF biologics (infliximab, adalimumab) specifically target these cascades.
Diagnosis & workup
Diagnostics & workup: - JAK2 V617F mutation testing: diagnostic for myeloproliferative neoplasms (present in 95% of polycythemia vera, 50-60% of ET and PMF) - CALR and MPL mutation testing: for JAK2-negative myeloproliferative neoplasms - STAT protein phosphorylation assays (research/specialized labs): assess pathway activation in lymphoproliferative disorders - Inflammatory markers: CRP (driven by IL-6-JAK-STAT3 signaling), ferritin, ESR - Immunophenotyping: T-cell, B-cell, NK-cell subsets to assess immune function in patients on pathway-targeted therapy - TB screening (QuantiFERON-Gold or PPD) before starting JAK inhibitors or anti-TNF therapy - Hepatitis B and C screening before immunomodulatory therapy