Cytokines are what kind of molecules?

• A. Lipids that store energy
• B. Group of proteins and peptides that are signaling compounds; they act via cell-surface cytokine receptors
• C. Antibodies produced by B cells
• D. Enzymes that digest pathogens

Answer: (B)

Cytokines are signaling proteins and peptides that act as messengers in the immune system. They’re produced by various cells, including immune cells, in response to infections or inflammation, and they exert their effects by binding to specific receptors on target cells. This binding triggers intracellular signaling that changes how those cells behave—promoting activation, differentiation, proliferation, or recruitment to sites of damage. They can act locally on nearby cells or travel through the bloodstream to have systemic effects.

This makes them fundamentally different from lipids that store energy, antibodies produced by B cells, or enzymes that digest pathogens.