Using DNA Nets to Capture Organisms

Why don’t you ever get sick from the same bug twice? The answer lies in the elaborate network of defenses that make up your immune system. The intimate relationship between immune system and pathogen has played an instrumental role in the evolution of nearly every living being on the planet. As organisms find novel ways to defend themselves, pathogens in turn find other ways to circumvent these defenses. For example: the ability of bacteriophages to wreak havoc upon entire populations of bacteria was soon stopped with the evolution of the restriction enzyme. The H1N1 virus, otherwise known as swine flu, mutated the ability to bind to human receptors, setting off one of the largest epidemics in recent history. But recently, scientists at the University of Geneva (UNIGE) have made a groundbreaking discovery nearly unprecedented in the field of immunology: the use of nets made out of DNA to trap and destroy pathogens.

Our immune system is the product of billions of years of evolution, tuned to respond to the vast majority of pathogens that could harm us. The immune system is comprised of two subsystems: adaptive immunity and innate immunity. Adaptive immunity relies on antibodies and lymphocytes to construct a targeted response to nearly any pathogen that invades our body. It is extremely powerful, but takes some time (usually a few days) to fully ramp up.

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A rendering of these ‘DNA nets’ (green). Note how they envelop the bacteria (pink), limiting their movement.

Photo by: NewScientist

The vast majority of pathogens that enter the body are repelled by innate immunity. Innate immunity uses nonspecific “eater” cells such as macrophages to recognize and eliminate unsuspecting pathogens. These macrophages have two methods for dealing with pathogens. First, they can directly consume the virus or bacteria and destroy it within the interior of the cell. But if the cell is too large or if its contents are toxic, they can also release chemicals into the environment that induce the pathogen’s destruction. These two methods have long been regarded as staples of innate immunity in mammals, reptiles, and other higher organisms.

But even though the complexities of our immune system have already been thoroughly researched and documented, the planet abounds with species possessing entirely different systems of immunity, many of which use novel techniques that could have far-reaching implications for medical research. One such discovery was made last week, when scientists as the University of Geneva uncovered a completely novel mode of innate defense used not by mammals, but by amoebas! Microbiologists had previously thought that innate immunity (as described above) was only used by relatively advanced organisms, but it appears that these amoebas have been utilizing it for millions of years.

Similar to the macrophages that make up our innate immune system, these amoebas have two different modes of attack. The first is to envelop the attacking pathogen and destroy it within the cell. This is nothing new to researchers; it has long been known that amoebas typically eat and digest their prey. You can even a watch a video of a feeding amoeba here!

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Of more surprise to the UNIGE scientists was the second function that they uncovered. Similar to how the macrophages within our body release chemicals to deal with larger pathogens, these amoebas have a mechanism of their own. However, instead of chemicals amoebas use poisonous nets of DNA that ensnare the organism and fatally poison it.

Because of the dramatic similarity between the feeding mechanism of the amoeba and human macrophages, researchers hope to use the amoeba as a model organism to uncover further information about how our own immune system works.

This discovery reveals a completely unprecedented function of not just amoebas, but of DNA as well. Though primarily used for the storage of genetic information, DNA has been shown to be used in mechanisms for cell defense. Because of the dramatic similarity between the feeding mechanism of the amoeba and human macrophages, researchers hope to use the amoeba as a model organism to uncover further information about how our own immune system works. The hope is that discoveries made through altering the genome of the amoeba will provide new therapies and methods for tackling disease that will be of tremendous benefit to the medical community at large.

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