If You Give a Mast Cell an Antigen


This is a slightly longer post than usual, but I didn’t want to gloss over anything important and risk comprehension for the sake of brevity. Also, I’m just really excited about my project and its future applications (I even added some quick cell watercolors to augment your learning because 1. art is fun and 2. I really had nothing better to do), so this is also me nerding out. Heh. So with that, let’s forge ahead!

You’re out at a restaurant with your family and decide to splurge on dessert; in particular, a fudge brownie sundae. Upon its arrival, it appears as magnificent as it sounded on the menu: a squat slab of dense cake, oozing gooey bits of chocolate chips, supporting a smooth scoop of vanilla ice cream, all topped with a delicate, twirling ripple of whipped cream. After only a few bites of this indulgence, however, your chest tightens. Your throat feels like it’s trying to suffocate itself which has greatly compromised your ability to breathe. You realize your dessert of choice is a hazard to your health not due to its extravagant calorie count, but rather the fact that it must have been in contact with peanuts some way or another, which, unluckily for you, you are deathly allergic to. At a young age, your immune system took offense to this lowly legume, and now you’re being rushed to the hospital in anaphylactic shock all due to your forgetting to question whether your dessert of choice had been created in a peanut-free environment.

What’s happening here? Clearly your body has rejected something it considers a threat to your health and therefore evil, but what’s behind this dramatic response?

In two words: mast cells!

A type of white blood cell involved in allergies and  fighting off pathogens, mast cells can be found at an array of sites around the body, most predominantly mucosal tissue (tissue that comes into contact with the outer world often, such as your sinuses) and the vasculature. Mast cells are stuffed with granules, which are essentially small sacks containing mainly proteases (enzymes that break down proteins) and some chemical compounds such as histamine. Mast cells also sport antibody receptors on their membrane that will bind with antigens when any are present in the body.

mast cell. . . aka cellular bean bag

When this occurs, a complex reaction pathway is triggered in the cell that ultimately leads to the release of the mast cell’s granules. The mast cell can regenerate new granules later, but what about the ones released? Well, they’re having a grand time causing havoc, either on pathogenic invaders or, in the case of an allergic reaction, on the body itself. 

When mast cells located around blood vessels come in contact with an antigen, degranulation occurs and the granules are released into the interstitial fluid and inevitably the bloodstream. The inner lining of blood vessels is made up of endothelial cells, which are simply a type of epithelial cell, and these cells endocytose (a fancy way to say “eat”) the granules. This choice of snack is just as poor as that of the hypothetical person with a peanut allergy eating something contaminated with peanuts, and the cells die, detaching from the basement membrane of the blood vessel. This leaves holes in the blood vessel, allowing fluid to rush in and the blood vessels to dilate, ultimately leading to a drop in blood pressure corresponding to anaphylaxis. So what exactly is it about the granules that triggers this cell death? That’s where my project for the summer comes in.

here’s the TL;DR version for your viewing pleasure

Mast cell granules contain, among other compounds, three different proteases that are unique to mast cells: tryptase, carboxypeptidase A, and chymase. It’s hypothesized that chymase is responsible for killing the endothelial cells. So, my summer thus far is focused on in vitro (basically, in a plastic plate and not something living — that would be in vivo and, well, super awesome) tests of this hypothesis, involving collecting granules from RBLs (Rat Basophilic Leukemia cells, which behave similarly to mast cells) to place on plates of cultured endothelial cells in varying amounts and seeing if the endothelial cells die. Then, to confirm that it is the chymase that is the main problem and not other compounds, the experiment will be run with a chymase inhibitor, and the amount of cell death will again be determined and compared to that of the experiment run without a chymase inhibitor. From there, the type of cell death must be determined (apoptosis, which is “clean” cell death? Or pyroptosis, which is basically cells exploding?). These are the first steps necessary in the process to eventually considering the use of an antichymase drug to use in tandem with an antihistamine to help completely squelch the symptoms of an allergic reaction. There’s a long way to go before that point, but I’m excited to be working on the very beginnings of such a project!


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