Immunity refers to the body’s innate ability to fight off diseases. The immune system does this by fighting off pathogens, which can range from small molecules to parasites. Our system is comprised of two main levels – we call these the innate immune system and the adaptive immune system.
The innate immune system is the first main level. This provides a quick first line of defense, and acts against a wide range of invaders. This system is comprised in part by physical barriers such as the skin, nonspecific chemical defenses like enzymes in tears and saliva that break down bacterial cell walls, and the normal healthy bacteria that live in and on us. If an invader circumvents these defenses, it will then face an inflammatory response which attracts other immune cells to the site of infection and increase blood flow to help ferry the cells there. These immune cells can engulf invading pathogens, destroy them upon ingestion and can kill cells infected with a virus.
The second main level of immunity is called the adaptive immune system. This level takes time before responding to an invasion. Once mobilized, it induces a response specific to a particular pathogen. This is different from the innate immune system; whose response is nonspecific. The adaptive immune system is the part of our immune system that remembers all the specific pathogens we have fought off. This is the basis of how vaccines work.
The adaptive immune system is comprised of two main cell types: T cells and B cells. Both kinds of cells are activated when they recognize a specific pathogen. B cells and T cells work together to sequester and destroy invaders.
As mentioned above, the immune system keeps a record of every microbe it has ever defeated, in types of white blood cells called memory cells. This means our immune systems can recognize and destroy the same microbe quickly if it enters the body again, before it can multiply and make you feel sick.
Some infections, like the flu and the common cold, have to be fought many times because so many different viruses or strains of the same type of virus can cause these illnesses. Catching a cold or flu from one virus does not give you immunity against the others.
The immune system is at once amazing, complicated and essential for our health and survival. Several different systems and types of cells work in unison throughout the body to fight off invaders, pathogens and clear up debris. The better we take care of ourselves the better out immune system work and take care of us.