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
Interleukin 1 (IL-1) is a potent cytokine. It is best described by which one of the following statements? 
Select and explain. 
A. Synthesis of IL-1 is inhibited in activated macrophages, B. It can be produced by natural killer cells, C. It exerts its effects on T and B cells as a costimulator, D. It is multimeric and consists of more than one protein
B: It can be produced by natural killer cells
Answer: B: It can be produced by natural killer cells 
Explanation: Interleukin 1 (IL-1) is produced by a variety of cells. Primarily, it is produced by activated macrophages or monocytes, although it can also be produced by activated B cells, keratinocytes, skin-layer hairy cells, and natural killer cells. IL-1 acts synergistically with IL-6 to stimulate production of IL-2. Human IL-1 consists of a and b forms, or two different proteins. They have limited similarity of amino acid sequence, and the P form is more abundant as a serum protein.