Interferon induction in human mixed leukocytetumor‐cell reactions: Evidence for restriction to a certain lineage expressing glycophorin A

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Abstract
This study reports the induction of interferon (IFN) in human mononuclear cells (MNC) by hematopoietic tumor cells. Only 3 out of 15 cell lines were capable of inducing IFN in the mixed leukocyte/tumor‐cell reaction (MLTR). K562, a pluripotent stem cell line and DUTKO‐1, a hybrid between K562 and Daudi (Burkitt lymphoma) induced high levels of antiviral activity (ranging from 50‐440 units IFN/ml). PUTKO‐I, a hybrid between K562 and P3HR‐1 (Burkitt lymphoma) induced very low levels of IFN (10 units/ml). This antiviral activity was produced by HLA‐DR+ adherent cells as revealed by different cell separation techniques, and shared well‐known properties of IFN γ (isoelectric point, inactivation by anti‐human IFN γ antibodies; species‐restricted protection). MLTR‐induced IFN induction could be blocked by enzyme treatment of tumor cells, but was still present when glutaraldehyde‐fixed cells were used for induction. Analysis of the cells by flow cytometry for expression of glycophorin A (GpA) revealed that expression of GpA correlated with the ability to induce antiviral activity in MLTR. Furthermore, isolated GpA could be used as a stimulant as well and the response to either K562 cells or soluble GpA was enhanced up to tenfold by the addition of a GpA‐specific monoclonal antibody.