Certain myeloid cells possess receptors for interleukin-2

A proportion of blasts from five of 10 cases of AML expressed receptors for IL-2 (IL-2R) when tested directly ex-vivo with monoclonal antibodies against the receptor. After in-vitro stimulation with various agents including TPA, gamma interferon and colony stimulating factor, the purified blast cells of all cases of AML tested (10 of 10) showed high levels (50-90% cells positive) of IL-2R expression. Granulocytic cells from the promyelocyte stage onwards lacked IL-2R both before and after in-vitro stimulation. In contrast, leukaemic promonocytes and normal peripheral monocytes expressed IL-2R both before and after stimulation. The receptors were detected with two different monoclonal antibodies (anti-Tac and 4H3--both IgG 2a antibodies) by indirect rosetting. In selected experiments, results were confirmed by fluorescence microscopy and by the APAAP technique. Normal monocytes possessed only small amounts of IL-2R since positivity was clearly detectable only by the indirect rosette assay. Irrelevant IgG 2a first-layer and second-layer-only controls were always negative. The endogenous nature of the IL-2 receptors was demonstrated by re-expression after capping and shedding. That the antigens detected were true IL-2R was confirmed by the fact that monoclonal antibody staining was blocked by recombinant IL-2. The restricted expression of IL-2R on early granulocytic and on monocytoid cells raises the possibility that IL-2 is important in the proliferation of these cell types.