PARTIAL CHARACTERIZATION OF THE RNA FROM LPS-STIMULATED MACROPHAGES THAT INDUCES THE RELEASE OF CHEMOTACTIC CYTOKINES BY RESIDENT MACROPHAGES

It is well established that exogenous RNA is incorporated into eukaryo tic cells and is able to exert various biological responses. Little, h owever, is known about the effects of such RNA on macrophages. In this study, we demonstrate that RNA extracted from macrophages stimulated with Escherichia coli lipopolysaccharide (LPS), referred to as L-RNA, in contrast to RNA from non-stimulated macrophages (N-RNA), induces th e release of a macrophage-derived neutrophil chemotactic factor (MNCF) and interleukin-8 (IL-8) from macrophage monolayers. The effect of L- RNA was dependent of the integrity of the polynucleotide chain and was not due to LPS contamination since its ability to induce MNCF and IL- 8 release was strongly reduced by RNase but was not affected by DNase or polymyxin B. The poly A(+) L-RNA and poly A(-) L-RNA fractions were able to induce the release of MNCF and IL-8, indicating that the L-RN A could be acting at transcriptional and translational levels. The dem onstration that actinomycin-D and cycloheximide inhibited the release of MNCF and IL-8 by L-RNA-stimulated macrophages confirms this assumpt ion. Fractionation of the total L-RNA by centrifugation on a 5-20% suc rose gradient showed that the L-RNA which sediments in the 4-5S region of the gradient is the only fraction capable of inducing the release of MNCF from naive macrophages. We have previously shown that macropha ge monolayers stimulated with interleukin-1 beta or LPS release a low molecular RNA which also sediments in the same 4-5S region. Taken toge ther, these results support our proposal that resident macrophages, wh en activated by injurious stimuli, in addition to secreting cytokines, also release a low molecular weight (4-5S) RNA which may act on the s urrounding macrophages to further stimulate the release of cytokines. This process would amplify the inflammatory response and would increas e the mechanisms involved in the defense response or tissue injury.