IL-1Ra size isoforms in the lysates of HepG2 cells, human primary hepatocytes, and the human keratinocyte cell line A431. Twenty micrograms of lysate proteins from HepG2 cells and human primary hepatocytes stimulated by IL-1β and IL-4 and from unstimulated A431 cells were electrophoresed on a 17.5% polyacrylamide gel, followed by electroblotting onto a PVDF membrane. Western blot analysis was performed using a mouse monoclonal antibody against human IL-1Ra that recognized all the described isoforms. Lane 1, recombinant icIL-1RaI; lane 2, recombinant sIL-1Ra; lane 3, A431 lysate; lane 4, HepG2 lysate; lane 5, human primary hepatocyte lysate.