LEGOs always come wrapped in those annoyingly hard to open plastic bags. If you rip them open too hard, the LEGOs will be flung all across the table, with the smallest pieces finding their way into the hardest to reach places. After several minutes of collecting the scattered LEGOs, you open the instruction booklet to begin your project.

After too many hours hunched over the table and more energy drinks than you care to count, a small army of “Star Wars” X-Wing fighters sit ready to take flight. At the moment though, they are inactive; wings closed tightly and their systems lifeless. The complement system of our immune system can be thought of as this army of LEGO X-Wing fighters just waiting for the call to action.

The human immune system is intricate and complex with millions of moving parts that work in coordinated efforts to keep us healthy and infection free. An important part of the immune system is something called the complement system. The complement system is composed of more than 30 different proteins that circulate in our blood and tissues: our LEGO X-Wing army.

Think of each different protein as a distinct style of X-Wing. Each are built just a little bit differently, their LEGO pieces arranged in a very specific way. Our army of X-Wing proteins circulate inactive in our blood as it is pushed throughout our bodies. They stay inactive until they are sparked into action by invaders like bacteria or viruses.

Their activation is triggered by a change in their shape. There are a variety of triggers that cause the complement system to activate but that activation is always achieved by the proteins changing shape. The fighters’ wings open with the snap of shifting LEGO pieces and power filters into their systems. Navigation clicks on and their targets are locked in. Their engines roar to life as the last moving LEGOs pop into place. They’re like little LEGO Transformers.

Once activated, the complement system’s X-Wing proteins do three specific and important things. They attach to and cripple the invader, making it hard for them to escape, and mark it so the rest of the immune system recognizes that it’s a target. Certain X-Wing proteins then travel from the site of infection to recruit more immune cells to come help out. Lastly, the fighters that are attached to the invader transform into a system that rips holes in the invader’s membrane so that it dies.

The X-Wing proteins make the invaders easier targets for the rest of the immune system to take care of. Without the complement system, our immune systems would be at a distinct disadvantage against the invaders constantly trying to take over. So, take some time and thank your army of X-Wing fighters. Their protection is invaluable.

Emily Leclerc is a graduate student at Boston University pursuing her master’s degree in journalism. She hopes to be a science writer.

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