The branch of biology that covers the study of the immune system in all organisms. Immunologists study the physiological function of the immune system, the complex system of the body that fights viruses, bacteria, fungi, and parasites, that may cause disease.
Deeper dive
The immune system is among the complex functions in the body. There are two layers to the system – the innate immune system and the adaptive immune system. The system also works in three phases – first the body detects that an enemy is trying to launch an assault, a messenger then sends for help to fight the threat, and then the body builds an army to counterattack to eliminate the enemy.
The innate immune system works quickly and is the part of the body that detects the enemy pathogen has entered the body. This part of the immune system tries to immediately neutralize the pathogen by creating proteins called cytokines and interferons, which both try to kill the invader as well as interfere with the pathogen’s replication. They also set off alarms in the body’s adaptive immune system that it may need help fighting the threat.
If the cytokines and interferons aren’t enough to stop the invasion, the second layer, or the adaptive immune system, joins the fight. The second layer is triggered by messenger cells, which grab pieces of the invader and carry it to the lymph nodes where specialized white blood cells are waiting to be called into service. In this Atlantic article, journalist Ed Yong likens the moment to being in a bar, where a bunch of mercenary killers, called T-cells, are waiting to be hired. Each T-cell can only kill one type of enemy, however, so when the ‘messenger’ shows up at the bar, the piece of the invader is shopped around to all the mercenaries sitting in the bar, until the messenger finds a match. Then the T-cell arms up by cloning itself into a huge army, and marches into the pathogen battle.
T-cells battles the pathogen in two ways. T-cells blow up cells invaded by the pathogen, and they activate another set of immune cells called B-cells, which produce proteins called antibodies. Antibodies are proteins that attach to pathogens and halt their ability to replicate in the body.
The adaptive immune system has a memory. Once the army has eliminated the pathogen in the body, most of the T-cells and B-cells die off, but the body keeps a few of the T-cells around in the lymph nodes just in case the pathogen tries to attack the body again. This is how vaccines work. They train the adaptive immune system to be ready for an attack. For a more detailed description of how the immune system works, look at this video produced by a Yale University School of Medicine immunologist Akiko Iwasaki.