Tuesday, February 06, 2007

(Secret) Viral Agents

In the last two days I've had two people independently ask me about the catching of colds in the Winter months. The Northern part of the States has taken a chill pounding over the past week, and you can expect a rise in sore throats and Kleenex sales.

The battle with the rhinovirus - the virus responsible for most colds - is one of an exponential arms race. With each new defense the body can throw down, the virus adapts, and the process begins anew ad infinitum. A major hurdle we're still dealing with as a species can be attributed to our upright posture
a severe weakness the virus and other bugs have been exploiting ever since we pushed off our knuckles and primarily moved around on two legs. But that's another story..

A virus is little more than a genetic bomb; most of it's components have evolved specifically to disrupt a human host's immune defenses with the core package a bit of RNA and replication protein to borgify and convert a cell into a virus factory.

The human host is no slouch and takes a layered approach to its considerable defense scheme. There are the anatomic barriers. The skin - a thick morass of cornified cells that appear like a gravelly, barren landscape on the microscopic level, sebum secreted from hair follicles give the skin an acidic, unwelcome feeling. The mucous membranes trap and hold invaders so ciliated hairs can ferry them up towards the mouth or nose for expectorations, as well as providing a home for local bacterial flora that soak up as much attachment space as possible in a competitive binding scenario. Should pathogens get all the way down to the gullet, that's usually a danger as well, as the low pH of the stomach will wilt all but the hardiest pathogens.

But should the virus be crafty enough or lucky enough to find a system compromised and get into the body, the host is not without further tricks. Upon detection by fingerprint-like molecules called antigens, the body can recruit dozens of different specialized cells to fight infection. Dendritic cells and other local watchdogs release signaling molecules called cytokines once they detect these antigens. First responder neutrophils arrive and wage a scorched earth warfare, triggering the inflammation response. Inflammation was originally described as having four qualities: rubor, tumor, calor and dolor. That is to say in modern terms, redness, swelling, heat and pain. All the lovely symptoms you'd associate with an upper respiratory infection, or any healing wound. The cytokine storm unleashed by the neutrophils can bring in a host of warriors depending on what the situation calls for. Massive, multi-nuclear macrophages to engulf and destroy necrotic tissues. Cytolytic killer cells designed to identify virally-infected host cells and punch holes in them with an immunologic cannon, faceted B-cells that churn out antibodies to bind up and help perturb and isolate antigens and eosinophils, the firemen of the body who come in to draw down the inflammatory inferno and bring things back towards normal operations.

Of course, these things don't happen instantly, as much as we'd like them to. It normally takes 3-4 days for a first response and 7-10 days for a human immune system to bring its full arsenal to bear and clear out an invading pathogen. The system is, much like the rest of our operations, susceptible to poor maintenance of the body as a whole. Fatigue, dehydration, poor diets, a lack of exercise - or lingering outside without a hat on in subzero temperatures like Mom warned out about - all such things can leave the body ripe for viral colonization.

A couple extra hand washings and a hat go a long way. Stay healthy this season!

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