Immune Health Refresher
The immune system is one of the most complex systems of the human body. It is a network of cells, tissues and organs that works together to defend humans and animals from “foreign” invaders, such as bacteria, viruses, parasites and fungi. The job of the immune system is to keep out the bad bacteria, or at least seek out and destroy them. It can recognize and remember millions of different enemies and can produce secretions and cells to match up with and wipe out nearly all of them. This is made possible by its elaborate and dynamic communications network.
Millions of cells organized into groups gather like clouds and pass information back and forth in response to an infection. Once immune cells receive the alarm, they become activated and begin to produce powerful chemicals that allow the cells to regulate their own growth and behavior. They can also enlist other immune cells and deploy them to trouble spots.
Central to a healthy immune system is the ability to distinguish between the body’s own cells, called “self” cells and foreign, or “nonself” cells. Normally, the body’s immune defenses coexist with cells that carry distinctive “self” maker molecules. When the immune defense encounters foreign cells or “nonself” organisms, they attack.
Immune System Structure
The immune system can be broadly segregated into two parts: innate immune system and the adaptive immune system.
Innate Immunity
The “innate” (meaning: ‘present from birth’) part of the immune system is so-called because it has a number of set strategies for recognizing and destroying infections, without needing to be trained to identify them.
The innate immune system is composed of several cell types that can engulf (eat) pathogens (phagocytosis), release chemicals and other soluble factors to directly kill pathogens (oxidative burst). The complement proteins present in serum are also considered part of the innate immune system and mainly function to identify pathogenic cells for attack but also have antibacterial properties on their own. Generally, innate immune cells migrate to sites of infection via the bloodstream, following a trail of increasing concentrations of complement proteins to the site of infection, and neutralizing the pathogens by engulfing them and killing them.
If the target cell is small enough, the phagocyte will engulf the target, bringing it completely inside the immune cell. Once the target is inside, the phagocyte will release highly reactive oxygen compounds (oxygen superoxide, hydrogen peroxide etc.) and other microbiocidal agents, which kills the pathogen and very often the phagocytic cell. If the target is too large to be engulfed by the phagocyte, these same reactive agents are released outside the phagocyte in a process called oxidative burst. In addition to killing the target, oxidative burst will often kill or damage both the phagocytic cell and surrounding host tissue.
Adaptive Immune System
The adaptive immune system, sometimes called the acquired immune system, isn’t able to respond instantly to infections, as it needs time to adapt (or learn/memorize how to recognize them). Once it has learned, however, it is extremely effective and is also able to remember particular pathogens that have previously infected the body, so that when (or if) they try to infect the body again, the next response is rapid, accurate, and effective. This concept is the basis for vaccinations most of us receive when young to prevent infection from certain pathogens.
The adaptive immune system is composed of lymphocyte cells (B cells and T cells) that can learn to identify pathogens and provide with a specific response to kill the pathogen. Adaptive immune cells produce soluble factors, such as antibodies, which neutralize the ability of pathogens to infect the host and antibodies also enhance the antimicrobial activities of phagocytes. The ability to produce antibodies to kill a specific pathogen is a learned or memory response and takes years to fully develop.
