Some perspectives on the transfer of cell-mediated immunity by immune-RNA

Regulatory RNA induces the production of IFN-gamma, but not IL-4 in human lymphocytes: role of RNA-dependent protein kinase (PKR) and NF-kappaB

Previous results with p9-RNA, obtained from lymph nodes of animals immunized with the peptide p9 of HIV-1, suggested that its effects on lymphocytes could be mediated by RNA-dependent protein kinase (PKR). Here we report that p9-RNA activates PKR leading to the degradation of the inhibitor I-kappaB alpha and the concomitant nuclear factor kappa B (NF-kappaB) activation. The fractionation of p9-RNA by affinity chromatography indicates that the poly A(+) p9-RNA is the fraction responsible for PKR activation. We also found that p9-RNA induces the production of interferon-gamma (IFN-gamma), but not interleukin (IL-4) since only IFN-gamma gene promoter contains NF-kappaB binding site. This study provides the first evidence that transcriptional control of gene expression by regulatory RNAs can be mediated by PKR through NF-kappaB activation. A model for the mechanism of action of poly A(+) p9-RNA is proposed.

Evidence for the involvement of the RNA-dependent protein kinase (PKR) in the induction of human cytotoxic T lymphocytes against a synthetic peptide of HIV-1 by regulatory RNA

Exogenous RNA molecules can be incorporated into eukaryotic cells and can exert a variety of biological effects. We have previously showed that exogenous RNAs obtained from lymphoid organs of animals immunized with synthetic peptides of HIV-1 are able to induce cell-mediated immune responses. In this study, animals were immunized with a synthetic peptide (pol: 476-484) of HIV-1, referred to as p9, which is a cytotoxic T lymphocyte (CTL) epitope. The RNA extracted from the lymphoid organs of animals immunized with p9 was termed p9-RNA. We have demonstrated that p9-RNA is active in inducing human CTL. The p9-RNA was also able to activate the RNA-dependent protein kinase (PKR) of human lymphocytes. The polyA(+) p9-RNA was the fraction responsible for the activation of this protein kinase. We also found that p9-RNA activates the transcription factor nuclear kappa B (NF-kappaB) by inducing the degradation of its inhibitor I-kappaB. Thus, these findings suggest that p9-RNA may act as a regulatory RNA and that the induction of CTL activity by p9-RNA could be mediated by PKR through NF-kappaB activation. It is known that CTL activity plays an important role in host defense against HIV-1 infection. Elucidating the molecular mechanism of p9-RNA could contribute to determining the basis for the use of p9-RNA as an immunomodulator in HIV-infected patients.

Effect of the calcium phosphate-mediated RNA uptake on the transfer of cellular immunity of a synthetic peptide of HIV-1 to human lymphocytes by exogenous RNA

It is known that exogenous RNA molecules can be taken up by eukaryotic cells and can exert a variety of biological effects both in vitro and in vivo. The modulation of human lymphocytes by exogenous RNAs has medical implications. The exogenous RNA used in this study was obtained from lymphoid organs of animals immunized with the synthetic peptide p12 of HIV-1 and was referred to as p12-RNA. Human lymphocytes were transfected with the p12-RNA and the transfer of immunoreactivity of p12 was assessed by the lymphocyte proliferation and the leukocyte adherence inhibition assays. Our results indicate that the transfer of cellular immune response to the p12 occurred in 9 donors (60%) who were named responsive individuals whereas 6 donors (40%) were non-responsives. We also found that the calcium phosphate-mediated RNA uptake method is effective in converting non-responsive into responsive donors. The calcium phosphate-mediated RNA uptake may also be used to increase the efficiency of RNA transfection in other models with medical implications and to contribute to a better understanding of the molecular events involved in the uptake of RNA. Our findings give support for the use of exogenous RNAs obtained from lymphoid organs of immunized animals with synthetic peptides of HIV-1 in the immune reconstitution of individuals infected with HIV-1.

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 eukaryotic cells and is able to exert various biological responses. Little, however, 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 the 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-RNA could be acting at transcriptional and translational levels. The demonstration that actinomycin-D and cycloheximide inhibited the release of MNCF and IL-8 by L-RNA-stimulated macrophages confirms this assumption. Fractionation of the total L-RNA by centrifugation on a 5-20% sucrose 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 macrophage monolayers stimulated with interleukin-1 beta or LPS release a low molecular RNA which also sediments in the same 4-5S region. Taken together, these results support our proposal that resident macrophages, when activated by injurious stimuli, in addition to secreting cytokines, also release a low molecular weight (4-5S) RNA which may act on the surrounding macrophages to further stimulate the release of cytokines. This process would amplify the inflammatory response and would increase the mechanisms involved in the defense response or tissue injury.