Interleukin 1 (IL-1) is a potent cytokine. It is best described by which one of the following statements?

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.