Purification of A Suppressor Lymphokine (SL) from a Human T-Cell Line

Human T leukemia cell line 81-66-45 spontaneously releases into the medium a suppressor lymphokine (SL), able to inhibit PHA-stimulated normal peripheral blood T cell proliferation. Ion exchange and gel filtration chromatography were used successfully to isolate and purify this immunosuppressive lymphokine from culture supernatants. When the purified suppressor lymphokine was characterized with SDS-polyacrylamide gel electrophoresis under reducing conditions, it was found to be a single protein chain of 66,000 daltons. Titration curves of the purified suppressor lymphokine indicated that the inhibitory activity is dose dependent. The suppressor lymphokine is cytostatic and its addition to the peripheral blood lymphocytes (PBL) did not change the cell number or cell viability. This factor was stable at pH 2.0-8.5 and at 56° C for 30 minutes. The structural relationship of this lymphokine with other T cell factors is discussed.