Parasites and Allergies

Rates of allergic conditions have gone up in recent years yet were virtually unheard of before the 19th century.  This has led some people to suggest what's known as the "hygiene hypothesis" - that leading an overly hygienic life, as we do nowadays, may increase the tendency for the immune system to react to things that it would normally ignore. To tell us more about the hygiene hypothesis, from Edinburgh University Professor Rick Maizels...

Rick -   Well it's essentially saying that the immune system that we have now evolved in the presence of many infectious organisms over eons of time and is best adapted to operate and protect us in the presence of various parasites and other infections.  And as I may mention in a moment, some of these infectious organisms are a little bit immunosuppressive, dampen the immune system for their own protection.  In the absence of those parasites and those microorganisms, the immune system now overshoots.  So you have instances perhaps - and this is the hypothesis - we have instances where the immune system is overeactive and unnecessarily targets innocuous environmental antigens, otherwise known as allergens as we've just been hearing from Pam.

Kat -   So basically, having worms meant that your immune system had something to do?  It was focusing on the worms and not on having an allergy.

Rick -   That's one interpretation, but the other interpretation is that the parasites are doing something actively to dampen an allergic reaction.

Kat -   So what do you think they're doing?

Rick -   What we wanted to do is to see whether there was a causal relationship.  Was it the presence of the parasites that actually protected, actively protected, against allergy? We showed that in the laboratory in mice, and then going further, we are able to show that our new friends, these T-regs, these regulatory T-cells, which Robert Lechler called the policeman of the immune system, they were preventing allergy in mice so that parasites were able to expand the body's own mechanism that protects us from allergy.

Kat -   So the immune system is using these cells to let the parasites get away with it and it's occupying them enough so that they're not amounting allergic reactions to things.

Rick -   It's a question of half full or half empty.  It's either the immune system is choosing to do this because it protects the body from allergy or it's the parasite manipulating this human immune system in its own interest, but at the same time, actually having a beneficial effect.

Kat -   But is it the case that it's just parasites that do this or other dirty things in our dirty world that might be doing this to us?

Rick -   I think it's much broader and I think what we've found is a point of principle and as Pam was saying how the rapid rise in allergies really in the last few decades, and of course, western populations reduced parasite loads many years before that.  So, I think what we'll find is that in the environment and in the sort of global spectrum of different infectious organisms, there are some particular species which actually have a beneficial effect, and are not necessarily dirty.  I mean, some of them may well be natural commensal microorganisms which expanded or decreased because of our diet and that's also been mentioned.  I think we have to take a global view of all these different influences.

Kat -   Because obviously, you don't want to infect someone with worms, just to make they're hayfever better.  How do you think you can take some of the discoveries you've made forward to make maybe viable preventatives or treatments for people with allergies?

Rick -   Well what we're aiming to do is to reproduce the effect of a parasite infection without having to have a live parasite within you.  And we've been able to do this firstly by collecting these regulatory T-cells and show that these will protect mice from allergy.  Now, we are isolating active substances from the parasite that themselves expand these regulatory T-cells in the lab, with the objective then of being able to replace live infection with an active principle from the parasite itself...