This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
True about cytokines is - 
Select and explain. 
A. It is always a polypeptide, B. It acts on protein targets, C. It takes pa in intrinsic enzymatic reactions, D. Chemotactic
A: It is always a polypeptide
Answer: A: It is always a polypeptide 
Explanation: They are a broad and loose category of small proteins (~5-20 kDa) that are impoant in cell signaling. They act on receptors Ref: Ananathanarayanan & Panikers textbook of microbiology 9th edition pg: 152