In the mid-eighties of the last century, extracellular-proteolipid complexes have been identified in
tumor patients and
circulating RNA was suggested to represent a specific secretory product of
cancer cells. The presence of specific types of
RNA in a variety of
cancer types proved to be useful in
cancer diagnosis. It has been suggested that extracellular
RNA and
DNA are not inert molecules, but contain
biological activities. Recent data have demonstrated that extracellular
RNA is likely to present the up to now undefined "natural foreign surface", serving as an initiating factor in blood coagulation in vivo. Yet, extracellular
RNA seems to have even more functions. Investigations on blood-brain-barrier have shown that extracellular
RNA mediates endothelial permeability. Ample success has been achieved in administrating
RNase in different animal models of
vascular diseases, thereby significantly delaying
thrombus formation and reducing
cerebral edema formation with neuroprotection in
acute stroke models. Furthermore, extracellular mammalian
RNA was found to decrease
tumor yield in a murine model system, suggesting that extracellular
RNA might trigger immune response. Finally, extracellular
nucleic acids were identified as danger signals involved in innate immunity related to neutrophil-mediated bacterial killing and haemocyte activation and coagulation in the insects. Thus, a new area of research on extracellular
RNA functions with promising future perspectives just started in the field of
inflammation and immunity.