Einstein Science Reporting for Kids
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9-Jul-2004

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What happens when snails get sick?



Scientists used to think that the two major groups of animals, vertebrates and invertebrates, protected themselves from getting sick in very different ways. A new study in snails suggests that both groups’ immune systems might be slightly more similar than we used to think. [Image © Science]

Full size image available here

Scientists used to think that the two major groups of animals, vertebrates and invertebrates, protected themselves from getting sick in very different ways. A new study in snails suggests that both groups' immune systems might be slightly more similar than previously thought.

One of the most powerful ways that humans and other vertebrates fight germs is called "adaptive immunity." When an invader enters the body, this part of the immune system responds with specialized cells called "lymphocytes" that are specially designed to recognize and attack that particular germ.



Snails and other invertebrates use a “one size fits all” kind of immune response, in which the same immune cells immediately attack any germ. [Image © Science]

Full size image available here

Once the body has produced a certain kind of lymphocyte, it never forgets how to do it. For some germs, this immune system memory means that they never get a second chance to invade. That's why most people only get chicken pox once, for example.

The reason the adaptive immune system can make so many different specialized lymphocytes is that its production centers are constantly churning out new cells using different combinations of genetic instructions. So, after a germ is identified, it's only a short time before a lymphocyte comes along that's the right match.

Snails and other invertebrates have much simpler type of immune response, called "innate immunity." This response works according to a one-size-fits-all kind of plan, in which the same immune cells immediately attack any germ.



When researchers studied the genes of these snails, they found that the produce cells using many different variations of certain genes, just like vertebrates do. [Image © Science]

Full size image available here

But, new findings in the 9 July 2004 issue of the journal Science suggest that invertebrates may also respond to germs in a way that's a little more like the adaptive immunity of vertebrates.

Si-Ming Zhang of the University of New Mexico and colleagues studied the genes of freshwater snails. They found that these animals also produce cells using many different variations of certain genes, just like vertebrates do when they produce lymphocytes.

The researchers don't know how the snails produce cells with so many genetic variations. In fact, the invertebrates may do it in a way that's completely different from what vertebrates do. But, Zhang's team thinks it's possible that all these variations may somehow help the invertebrates protect themselves against germs.

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