Peptides and enzymes in the venom break down cell membranes. When these cells are neurons, it causes the cell to send signals back to the brain, which is experienced as pain.
In the human body there are cells called B-cells, which are a type of lymphocyte, or white blood cell. They make antibodies which identify and neutralize invading pathogens, including the wasp venom.
Another type of lymphocyte are T-cells. These cells attack other cells that have already been infected by viruses, unlike B-cells which attack antigens floating around in the bloodstream. White blood cells are one type of specific defense in the human body which means they are designed to protect against a certain type of invader.
Wasp venom contains microbes, which cause disease and infection, or in Alec's case an allergic reaction. Phagocytes at a type of cell in the body that kills microbes, often times by absorbing them.
The wasp sting got inflamed because of immune responses in the human body. The function of inflammation is to eliminate the initial cause of injury and start tissue repair.
After a few more hours in the hospital Alec was discharged from the hospital and after that, he always made sure he had an epi-pen with him