A mosquito lands on your arm and injects its chemicals into your skin and begins to feed, you wouldn’t even know it was there if not for the red lump that appears accompanied by a telltale itch. It’s a nuisance but that bump is an important signal that you’re protected by your immune system, your body’s major safeguard against infection, illness and disease. This system is a vast network of cells tissues and organs that coordinate your body’s defenses against any threats to your health, without it you’d be exposed to billions of bacteria viruses and toxins that could make something as minor as a paper cut or a seasonal cold fatal very harmful. The immune system relies on millions of defensive white blood cells also known as leukocytes that originate in our bone marrow, these cells migrate into the bloodstream and the lymphatic system(a network of vessels which helps clear bodily toxins and waste)so our bodies are teaming with leukocytes and there are between 4,000 and 11,000 in every micro liter of blood as they move around.
Leukocytes work like security personnel constantly screening the blood tissues and organs for suspicious signs, this system mainly relies on cues called antigens, these molecular traces on the surface of pathogens and other foreign substances betray the presence of invaders as soon as the leukocytes detect them, it takes only minutes for the body’s protective immune response to kick in. Threats to our bodies are hugely variable so the immune response has to be equally adaptable, that means relying on many different types of leukocytes to tackle threats in different ways despite this diversity. We classify leukocytes in two main cellular groups which coordinate a two-pronged attack
First, phagocytes trigger the immune response by sending macrophages and dendritic cells into the blood as these circulate they destroy any foreign cells they encounter simply by consuming them, that allows phagocytes to identify the antigen on the invaders they just ingested and transmit this information to the second major cell group orchestrating the defense, the lymphocytes, a group of lymphocyte cells called T-cells go in search of infected body cells and swiftly kill them off meanwhile B-cells and helper T-cells use the information gathered from the unique antigens to start producing special proteins called antibodies. Each antigen has a unique matching antibody that can latch onto it like a lock-and-key and destroy the invading cells.