Functional and physical association of a cell surface phospholipid and interleukin-2 receptor p55(alpha) subunits

A phosphatidylcholine-like phospholipid expressed in the outer leaflet of the cell membrane shortly after mitogenic activation of T-cells is described, based on the binding of monoclonal antibody 90. 60.3. Expression of the 90.60.3 phospholipid antigen in T-cells is activation-dependent. Once expressed, the 90.60.3 phospholipid is in direct physical association with the interleukin-2 (IL-2) binding domain of IL-2 receptor alpha subunits, but does not affect IL-2 binding. The association is specific, because the 90.60.3 phospholipid is not found in association with other domains of IL-2 receptor alpha subunits, or near IL-2 receptor beta or gamma subunits. Culturing cytokine-dependent cell lines in the presence of monoclonal antibody 90.60.3 potentiates IL-2-dependent cell survival and proliferation in a dose-dependent manner. In contrast, IL-4-dependent responses are not potentiated. Taken together, the data suggest that specific plasma membrane phospholipids expressed in the outer leaflet after T-cell activation associate with the IL-2 binding domain of IL-2 receptor alpha subunits (and perhaps other cytokine receptors), and may play a role in regulating receptor mobility or signal transduction.