The cascading pattern of one cell triggering an action in another cell continues with this mast cell, but with one important difference: for an action to be triggered, two of the red Y-shaped bound antibodies, called IgEs (Ig short for immunoglobulin), have to bind to one molecule of the bad stuff (green spiked spheres in frame 2). Can ANYONE explain why this is the case?
Once this occurs, the mast cell releases histamine (cyan blue particles, frame 3), which triggers your nose to run, the swelling, the itching, and the sneezing. All the hallmarks of allergies.
Another really important note is that these allergic responses occur the SECOND time you are exposed to the bad stuff. The FIRST time is like the practice run, where the cells learn that the bad stuff IS bad. Our immune system is so smart that the red, Y-shaped IgEs that do the "recognizing" stay in your body for weeks, as if they are anticipating that if the bad stuff could get in once, it'll get in again, very soon after.
It may seem crazy that we are made to be so miserable with our allergic responses, but without the immune system, we would be in far worse shape!