Complex sentence: IL-1RA is an agent that binds non-productively to the cell surface interleukin-1 receptor (IL-1R), the same receptor that binds interleukin 1 (IL-1), preventing IL-1 from sending a signal to that cell.
Split into simpler sentences: IL-1RA, is an agent that binds non-productively to the cell surface interleukin-1 receptor (IL-1R). Hence IL-1RA prevents IL-1 from sending a signal to that cell.