Evidence That the Interferon-induced Daudi Cell Human Lupus Inclusions Are de novo Synthesized Complexes of Ribonucleoprotein and Membrane

Abstract

Quantitative electron microscope autoradiography has been used to define the macromolecular composition of the interferon-induced human lupus-type inclusions (LI) in the human B lymphoblastoid cell line, Daudi. LI were first apparent in Daudi cell cultures 12 h after the addition of 100 units/ml of the purified recombinant human leukocyte interferon, IFLrA. Radiolabels were added at this time and allowed to incorporate over the following 12 h during which an estimated greater than 99% of the LI material present at 24 h was formed. The LI-incorporated radiolabels were present only during this discrete 12-h period after the interferon activation of LI cell pathways in order to detect LIs de novo synthesized macromolecular components. The estimate relative specific activities of the LI-incorporated radiolabels were: choline at 4.042, mannose at 2.631, uridine at 0.664, glucosamine at 0.578, and amino acids at 0.477. With thymidine the estimated LI specific activity was 0.000. LI isolated from whole cells retained the tubular elements and the interwoven membrane network. These results provide direct evidence that the interferon-induced Daudi cell LI are de novo synthesized complexes of ribonucleoprotein and membrane.