The cells of our immune system are the guardians of the human body, forever contending with various unwelcome intruders from viruses to drugs to lowly yet painful splinters. They are as industrious as they are indispensable.
Each cell of the immune system has its own objective, its own do-or-die mission. Some of our guardians devour bacteria and fungi in a process known as phagocytosis. Others produce carefully tailored antibodies earmarked for the destruction of pathogenic organisms. A few of these cells are loaded with noxious granules that can erupt from the cell, unleashing enzymes, peroxides, and immune-modulating molecules in everything from pollen grains to parasites to peanuts. Eosinophils are in this last class of microscopic warfare.
Eosinophils get a bad rap for their role in instigating the symptoms of asthma and allergies. Upon exposure to, say, cat dander, the eosinophil cells of allergy sufferers discharge their toxic contents provoking dripping noses, glazed red eyes, and explosive sneezing. But they’re responsible for more than just a few vexing symptoms, as those same harmful enzymes and potent molecules can do further damage as they eat away at our body’s proteins and tissues. Eosinophils are also main actors in other, far more serious immune responses and diseases, lying at the heart of anaphylaxis, an overwhelming and sometimes fatal response in individuals susceptible to penicillin, shellfish, or other allergies.
But where eosinophils really excel is in combating infections with parasitic worms that invade bodily tissues – they are highly specialized worm terminators. So key is their role in combating parasitic helminths that their presence is the sine qua non of diagnosing an invasive worm infection. But how these cells recognize parasites and then go about recruiting more of their kind was largely unknown until this past summer. A study published by the University of California, San Francisco not only identified the smoke signals that eosinophils use to communicate, but also filmed some truly awesome time-lapse footage of these cells doing what they do best: annihilating worms (1).
In the video, eosinophils are seen attacking a worm, the nematode Caenorhabditis elegans, embedded in a three-dimensional gel matrix. Over a period of just eighty minutes, thousands of cells swarm the spasming worm, with the line of attack increasing in intensity as more eosinophils muster to battle. Clusters of cells form around the worm, expelling pro-inflammatory molecules, toxic substances and phagocytizing debris (2).
The study showed that eosinophils are uniquely attracted to worms, even when placed in a synthetic agarose gel without the supporting backup of an existing immune system, suggesting that there’s an evolutionarily conserved feature of eosinophils that recognizes parasitic worms. Upon identification of an invading worm, these cells then release a signaling molecule known as leukotriene B4 that recruits fellow eosinophils to the site of attack.
The cells of the immune system are microscopic guardians that guard the borders of our bodies, unceasingly vigilant, forever on duty, and always prepared to launch a drastic defensive. We’ve always relied on these cells, but have now deduced something of our eosinophils’ battle plan, the nature of their encoded communications, and have also gained a quick glimpse into the theatre of microscopic warfare.
Learn more of the study and see more of footage of the eosinophils vs. worm battle by checking out the published article here.
Eosinophils can be found in several medical conditions, from endocrine disorders to certain cancers. Find out more here.
1) ML Patnode et al. (2014) Leukotriene B4 amplifies eosinophil accumulation in response to nematodes. J Exp Med. 211(7): 1281–1288
2) C.A. Behm and K.S. Ovington. (2000) The Role of Eosinophils in Parasitic Helminth Infections: Insights from Genetically Modified Mice. Parasitol Today. 16(5): 202-9