There are two functionally comparable forms of IL1: IL1A and IL1B, that are encoded by two different genes. IL1B is the predominant form in humans while, it is IL1A in mice. Both forms of IL1 bind to the same receptor and therefore show similar, if not identical, biological activities. Latter include but not limited to, stimulation of T-helper cells, promotion, proliferation and synthesis of immunoglobulins and the activation of fibroblasts and NK cells. Unlike IL1B, the IL1A precursor does not require processing before it can bind to the receptor. Monocytes are the main source of secreted IL1B while human keratinocytes are known to express large amounts of IL1A. Recombinant Human IL1A is a non-glycosylated polypeptide of 18 kDa.