Sunday, October 15, 2006

The hygiene hypothesis

No, this doesn't have anything to do with washing any part of you, not directly anyway.

Have you ever wondered about asthma? Or hay fever? I mean, what is up with those afflictions? It seems in these cases our immune systems has run amok. There is a hypothesis that our bodies have a specific immune response to parasitic infection, and in environments that lack parasites, that immune response can get activated in the presence of otherwise innocuous substances (i.e. pollen, dust, etc.).

One of the observations that led to this hypothesis was that populations that have a high incidence of parasites, have a very low incidence of asthma and vice versa. This evidence is only correlational, however. In other words, just because asthma and parasites don't show up together, doesn't mean that the root cause is the same. Other factors may be at play, especially given that the major difference between the two populations is how developed the country is. Given that major difference - hygiene, vaccination and the use of antibiotics in more developed countries may also be factors. But let's say there is a correlation.

One interesting biological note, you can have a chronic parasitic infection... meaning that your immune system doesn't go haywire on you, and you and your bugs can live quite a while together (maybe not happily, but you get the picture). Prolonged asthma attacks; however, can send you to the emergency room. If this is the same biological response what is different that you can survive a parasitic infection and not asthma? Let's delve into the immunology behind this a little...

One of the kinds of antibodies floating around in your system, IgE, can bind to a type of cell that releases loads of sneezy, itchy chemicals... histamine is one of them, I'm sure you've seen the commercials. For that to happen; however, two IgE's to the same substance - let's say juniper pollen - have to be immediately next to each other on the cell. You'd have to flood your system with that particular IgE and sometimes it takes years for that to happen. That is a simple explanation for why allergies take a couple of years to show up. But when they do, you are a itchy red ball of mucous, or your lungs fill up with fluid, or your airways disappear.

Although IgE is also involved in a parasitic infection, you notice that the infection person's immune system doesn't go into overdrive. Hypothesis: It may be that the production of another antibody, IgG4, may inhibit the allergic response. Observation:IgG4 isn't present in asthma or hay fever like afflictions, although it is in parasitic infections. Since hearing about this problem in graduate school, I've thought that if I could develop something that would induce the production of IgG4, I'd be rich. Turns out for really bad allergies, people can undergo a form of immunotherapy where they get allergy shots every few weeks for 3-5 years. This kind of treatment in itself would suck, however, if you manage to stick with it, it does seem to induce the production of IgG4.

Well, there are scientists out there that are looking for ways to treat our over-active immune systems, and not just the symptoms either. A search of Peter Creticos' research over the last two decades culminating in a report that a 6-week inoculation protects the allergy sufferer for 2 hay-fever seasons (so far) demonstrates he is looking down this road for allergy and asthma sufferers. I'm hoping he gets rich from this.

1 comment:

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