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Genesis of a Historical Novel

Monday, April 30, 2007

reflections on the immune response

Another weekend goes by--very pleasantly, in the main, although both Kimmie and I are fighting off simultaneous headcolds. Dosing ourselves with tincture of echinacea, we're holding the virus at bay thus far, having both started to feel symptoms on Friday night. We reckon we must have caught it together from the same source, but aren't sure where. Two possibilities: one of Kimmie's family members was a vector when three of them came over for lunch a week ago Sunday--giving a long-sounding incubation period of five days; or we picked it up when we had lunch together on Thursday at The Burgoo restaurant near her work. Neither of our waitresses appeared to be infected, but who knows what goes on in restaurant kitchens? I picture some cold-ridden cook sniffling his way through soup- and stew-preparation.

"Another reason to eat at home," said Kimmie last night, while we speculated on the source of our infection.

But in fact we don't know. Viruses arrive, board our cells like pirates, and then must be dealt with.

I used to think of viruses as more intimidating than, say, bacteria, just because they are not treatable with antibiotics, and their method of attack always involves a direct invasion of our cells and subversion of the cells' own reproductive process--creepy. Viruses are much, much smaller than cells and do not eat, breathe, or indeed metabolize in any way. They have no propulsion system of their own but move passively wherever they're driven. How can the body deal with such an invader?

I was heartened by reading the book Microbiology the Easy Way last year (I wrote a review of the book on Amazon.com, if you're interested). Our immune systems are wondrous and complex things, and include powerful antiviral weapons. One of these is a class of proteins called interferons. When a cell is invaded by a virus, the virus's commandeering of the cellular reproductive system causes the cell to produce interferons. Although an infected cell is generally doomed, it releases these interferons which are picked up by neighboring cells. The interferons cause these other cells to switch on genes for producing special proteins that can block viral reproduction. So when the viruses arrive in these cells, the cells are ready: before the viruses can invade the cell nucleus and subvert its DNA-processing, they are stuck with proteins that prevent them from functioning or can dissolve the viral nucleic acid. The viruses or their dissolved parts can then be broken down by the cell like regular cellular waste. Amazing!

I don't know whether this is how the body deals with the virus for the common cold, but if it does, I imagine the virus landing, possibly riding on water droplets that we inhale or smeared on our membranes if we touch our mouth, nose, or eyes with unclean hands, and invading the cells of our mucous membranes. The death of cells and their released products would trigger an immune response, which we experience as the symptoms of our cold. Neighboring cells arm themselves against the virus, which, multiplying furiously as it kills infected cells, leapfrogs over them to other cells that aren't warned yet. The cold spreads from throat to nose to lungs as the virus looks for pristine defenseless cells to invade. Eventually all the cells susceptible to the virus have been warned and are no longer vulnerable. The invaders are immobilized, dismantled, and flushed into the body's wasted system. The dead cells are replaced by reproduction among the survivors. By the end of the cold the body has probably produced antibodies to the virus--special molecules that fit the virus's exterior chemicals like a key in a lock, enabling the body's white blood cells to recognize them as invaders and vacuum them up before they can enter cells. The next time that type of virus invades, it finds the body much better prepared to take it out of circulation.

I bought the book on microbiology in December 2005 as part of my inquiry into the mystery of identity--for our immune system is a vigorous and complex assertion of our physical identity. It is the border patrol and immigration office of our body, getting rid of everything that is not "us". Our immune system knows what "we" are--but do we know what "we" are?

It's a mystery. Right now I'm grateful that my immune system seems to be strong and on full alert. Go, team, go.

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