Immune system ↗Receptors change cell state
Cytokines can alter transcription, metabolism, survival, proliferation, differentiation, antimicrobial function, and mediator production.
IMMUNE / 03
Signals need
place and time.
Cytokines change behavior, chemokines direct movement, complement amplifies recognition, vessels control delivery, and liver and brain create a coordinated acute-phase response.
The same signal can differ by target
Effect depends on receptor expression, cell state, concentration, timing, competing signals, tissue, and feedback.
Gradients encode direction
Chemokine receptors guide leukocytes toward increasing ligand concentration while adhesion and tissue barriers control access.
Vessels become a delivery gate
Endothelial adhesion molecules, permeability, tone, and coagulation allow selected cells and proteins to leave blood locally.
Induced brakes limit amplification
Receptor internalization, suppressor proteins, decoy receptors, regulatory cytokines, mediator degradation, and cell death restrain signaling.
Three routes recognize surfaces
Classical, lectin, and alternative pathways begin differently but converge on activation and amplification of central complement components.
C3 fragments mark targets
Deposited complement products improve phagocyte recognition and can help capture antigen in adaptive immune structures.
C3a and C5a signal inflammation
Small cleavage fragments influence vascular permeability and strongly recruit or activate selected leukocytes.
Membrane attack can damage targets
Late components assemble a membrane complex most effective against selected susceptible organisms and surfaces.
Host surfaces carry protection
Soluble and membrane regulators restrict convertases, inactivate fragments, and prevent uncontrolled terminal complex formation.
Liver output changes
IL-6 and related mediators change CRP, fibrinogen, serum amyloid A, hepcidin, complement, albumin, and other hepatic proteins.
Hepcidin redistributes iron
Inflammatory hepcidin reduces iron export, potentially limiting microbial access while contributing to anemia when sustained.
Brain raises the set point
Immune signals induce prostaglandin-mediated hypothalamic thermoregulation, chills, heat production, and later heat loss as the set point falls.
Behavior and metabolism reorganize
Fatigue, sleep change, reduced appetite, endocrine shifts, muscle catabolism, and fuel redistribution can accompany systemic defense.
Measurements are nonspecific outputs
CRP, ESR, ferritin, procalcitonin, cytokines, and temperature reflect overlapping processes and require population, cause, timing, and assay context.