INHIBITORY ACTIVITY OF SOLUBLE IL-2R IN SERA, ASCITES AND CULTURE SUPERNATANTS FROM MURINE LEUKEMIC-CELLS

The effect of sera from mice bearing a T cell lymphoid leukaemia (LB) and the supernatants from short term cultures of the tumour cells were studied on cell proliferation using syngeneic and allogeneic normal a nd tumour cells. An inhibitory activity was demonstrated in 24-48 h su pernatants of LB cells in culture and disappeared after 4 days of cult ure. Inhibitory activity was cytostatic but not cytotoxic and was non- specific since it inhibited the growth of both syngeneic and allogenei c normal and tumour cells. Such activity was found in the 10(5)-1.3 x 10(5) Mr serum fraction after a Sephacryl S200 chromatography. Though sensitive to protease, trypsine or neuraminidase treatment, which indi cated its glycoprotein nature, it remained stable after heating or fre ezing-thawing cycles as well as after alkaline, acid or hyaluronidase treatment. Addition of exogenous IL-2 abrogated inhibitory activity. E LISA showed the presence of soluble IL-2R both in LB conditioned mediu m and in above serum fraction. It is demonstrated that the inhibitory factor, soluble IL-2R, is produced by LB leukaemia cells, then secrete d into blood and ascitic fluid or released into culture supernatants. Soluble IL-2R exerts inhibitory activity blocking cell proliferation a nd modulating immune response by binding to free IL-2.