Sunday, July 16, 2006

Detecting Viral RNA

A Biocompare news article entitled 'Immune System Response To Viral DNA Is Unique' discusses recognition of foreign DNA; a vital function in defending against viral as well as bacterial pathogens. Some comments follow. Passages from the referenced article appear in italics.

Although there are countless types of viruses, they can all be placed in two categories based on the type of nucleic acids that comprise their genome: viruses made of RNA and viruses made of DNA. Infected cells sense the presence of foreign nucleic acids as viruses replicate inside them and distill the problem of recognizing a dizzying array of viruses into a relatively simple mechanism for turning on the immune response.

"It is well established that such a pathway exists for detection of viral RNA inside infected cells," Stetson said. "In contrast, very little is known about whether cells can detect foreign intracellular DNA or how this system might function."

Different detection pathways, in addition to other factors, might explain pathogen dynamics. For example, RNA viruses that utilize the reverse transcription process can be classified into distinct families. Retroviridae are associated with vertebrates, metaviridae with fungi and invertebrates and pseudoviridae with invertebrates. Variation in cellular mechanisms that distinguish between different types of RNA offer intriguing explanatory possibilites.

"We found that this novel pathway seems to function differently from all other known nucleic acid sensors," Stetson said. "The unique immune response activated by foreign DNA suggests that DNA viruses and RNA viruses are detected by different mechanisms."

Stetson said one important question raised by these findings is how this newly described system avoids responding to genomic DNA that is contained within all cells.

"If this 'tolerance' to self DNA were to break down, cells might mount an antiviral response against their own DNA," he said. "Further characterization of this pathway will shed light on the mechanisms of antiviral responses and how cells discern viral and self-DNA."

Malfunction involving nucleic acid detection mechanisms could indeed be linked to diseases whose causes are still unknown.


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