The marine sponge is the oldest and simplest multicellular animal on earth, having originated over a billion years ago. Because of its simplicity, this creature has become a useful tool for medical researchers trying to unravel the workings of the human immune system.

 

Because the human immune system is so complex, it is very difficult for researchers to study. Sponges grow in clusters from rocks on the ocean floor, and they consist of colonies of like cells, which organize themselves into a series of filters that strain nutrients from the water. The marine sponge is a useful model for the human immune system because it illustrates the workings of an immune system at the cellular level.

 

In the early 1900's, it was discovered that when cells of sponges are separated in a seawater solution, they soon clump together to form tiny new sponges. When cells of two different types are mixed, however, they aggregate only with their own kind.

 

These pioneering experiments showed that even these simplest of animals are able to distinguish between "self" and "non-self," a capability which is an important feature of immune systems.

When this recognition system breaks down, painful autoimmune diseases such as rheumatoid arthritis, gout and lupus erythematosus can result. In these autoimmune diseases, white blood cells mistakenly attack the body's own cells because the immune system's ability to distinguish between "self' and "non-self" is malfunctioning.

 

The Beard of Moses sponge owes its skill at cellular recognition to a protein molecule called an aggregation factor, which is released by the sponge into the seawater. The aggregation factor acts as a sort of biochemical glue, locking into specific sites on the surfaces of free-floating sponge cells and encouraging them to link up at these locations.

 

Inflammation is a by-product of the body's immune system; and in many conditions, it is part of the normal healing process. White blood cells called neutrophils are part of the inflammation process in humans, where they are among the cells dispatched by the immune system to the site of a foreign invader. Like sponge cells, neutrophils link up with each other by a series of related protein molecules which are released into the bloodstream when a foreign material is present. These proteins hook onto special receptors on the surface of the foreign material, and inflammation results.

 

Medical researchers are studying this inflammation process in the sponge. Interestingly, when anti-inflammation agents such as aspirin are added to aggregates of sponge cells, the aggregation process is interrupted -- in the same way that the clumping of neutrophils is halted by the presence of similar anti-inflammatory drugs.