THE ROLE OF IL-2 INTERACTION WITH P75 AND P55 RECEPTOR MOLECULES IN THE STIMULATION OF CELL-PROLIFERATION

This report addresses the role of individual IL-2 binding proteins of the IL-2 receptor in the stimulation of cell proliferation by IL-2. Mu rine IL-3-dependent cell lines were established which expressed the hu man p75 IL-2-binding protein, in the absence or presence of the human p55 IL-2-binding protein. Whereas p75 expression was sufficient to con fer response to an intermediate (half-maximal stimulation at 100 pM) c oncentration of IL-2, additional expression of p55 increased the sensi tivity of the cells to half-maximal stimulation at 10 pM IL-2. A mutan t IL-2 molecule, Lys-20 IL-2 which is known to be defective of p75 int eraction, was unable to stimulate cells expressing only p75: p55 co-ex pression could restore its activity. Under conditions of low p75 expre ssion, Lys-20 IL-2 could act as an antagonist of wild-type IL-2 action . These data support a role for p55 in the enhancement of responsivene ss to IL-2.