Why do we have allergies?

Allergies are really annoying, and sometimes deadly. They are caused by our immune system overreacting to a stimulus and causing the allergy symptoms, sometimes even death. So, how is this an evolutionary advantage? Why hasn’t natural selection removed this?

A good article at Gizmodo explains how a Russian researcher, Ruslan Medzhitov, has studied allergies and the immune response.

Allergies make a lot more sense in terms of evolution when seen as a home-alarm system, argues Medzhitov. Toxic chemicals, whether from venomous animals or plants, have long threatened human health. Allergies would have protected our ancestors by flushing out these chemicals. And the discomfort our ancestors felt when exposed to these allergens might have led them to move to safer parts of their environment.

It looks like the allergic response isn’t triggered by the presence of an allergen, but when that allergen starts harming the body–destroying cells. Essentially, allergies are your body’s way of trying to remove the allergen. Coughing, itching, sneezing, and tears are all ways that bodies try to get things out of the body. More research needs to be done on this.

Sitting on Cullen’s lab bench is a plastic box that houses a pair of mice. There are dozens more of these boxes in the basement of their building. Some of the mice are ordinary, but others are not: using genetic engineering techniques, Medzhitov’s team has removed the animals’ ability to make IgE. They can’t get allergies.

Medzhitov and Cullen will be observing these allergy-free mice for the next couple of years. The animals may be spared the misery of hay fever caused by the ragweed pollen that will inevitably drift into their box on currents of air. But Medzhitov predicts they will be worse off for it. Unable to fight the pollen and other allergens, they will let these toxic molecules pass into their bodies, where they will damage organs and tissues.

This would show that allergies are helpful to the body and there would be selective pressure for allergies as an adaptation.

Staph bacteria subverts the immune system

An article in Science Life explains how one of the persistent staph varieties manages to defend against the host’s immune systems. Staphylococcus aureus is a nasty bug that about 20% of people frequently have. A mutation in two genes allow the bacteria to cause the immune systems NETs to create a chemical that kills macrophages, white blood cells that would normally kill the bacteria. A very devious system.

Now that we know this, scientists can use this information to develop therapies that can fight against it. This will greatly help against methicillin-resistant S. aureus (MRSA), which is antibiotic resistant.