A method of treating inflammation by administering a therapeutically effective amount of a human immunosuppressant protein (HISP) to a subject is presented. The inventors have discovered a novel immunosuppressive protein purified from the supernatant of hNT cell culture. The immunosuppressant protein has a molecular weight of about 40-100 kDa, an isoelectric point of about 4.4, a net ionic charge and is capable of suppressing T-cell activation, T-cell proliferation and the production of IL-2. This protein can be used in treating inflammation, preventing graft rejection after transplantation, treating autoimmune diseases and suppressing allergic responses as well as other uses.