Treatment of a human monocyte-like cell line (U-937) by (2′-5′)ApApA, the 5′dephosphorylated product of (2′-5′)oligo-isoadenylate [oligo(A)] synthetase, an interferon-induced enzyme, was able to induce differentiation, mimicking the effect of interferon treatment. Treatment of U-937 cells with (2′-5′)ApApA resulted in morphologic changes, new (monocyte-associated) membrane antigen expression, and acquisition of the capacity to mediate antibody-dependent cellular cytotoxicity (ADCC). (2′-5′)ApA and (3′-5′)ApApA were without effect. A myeloid cell line (HL-60) which differentiates in response to other agents, but not to α-interferon, was not able to differentiate in response to (2′-5′)ApApA, despite the ability of interferon to induce (2′-5′)oligo (A) synthetase.
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