Cellular immunity, also known as cell-mediated immunity, is an important aspect of the immune system that allows the body to attack invading organisms on a cellular level. It is paired with humoral immunity, the part of the immune system that involves an antibody response. Both types of immunity are a critical part of a healthy and functioning immune system.
In cellular immunity, the body recognizes infected cells and kills them, using cells like macrophages and natural killer cells. These cells are designed to trigger cell death, ensuring that infected cells do not replicate and allow the infection to spread. CD4 cells, also known as helper T cells, play an important role in cellular immunity by focusing and directing attacks on infected cells so the immune system can accurately and effectively target an infection.
Many microorganisms target the body by attempting to hijack cells. The cell is used to harbor the infectious organism, and some are even capable of repurposing the cell to their own ends, using the cell for reproduction and a source of nutrition. Cellular immunity allows the body to identify cells that have been compromised so they can be destroyed, minimizing an organism's ability to spread through the body.
The immune system uses a series of interconnected systems to catch infectious organisms. One element alone could not eliminate an infection, but by working together, the various aspects of the immune system can effectively target and clean up infectious material, as well as isolating toxins. Destroyed and neutralized infectious material makes it way into the lymph nodes and will eventually be eliminated from the body.
New immune cells are constantly being produced. Every time the body battles an infection, it learns to recognize new infectious material and this information is passed on throughout the immune system so it can respond quickly in the future. The cells involved in cellular immunity must constantly be replenished because many are short-lived and during an active immune response, many of the cells will die.
Most people are only aware of their immune systems when they are not working. The immune system is constantly in action, neutralizing threats before people are alerted to their presence. Sometimes, the system breaks down. Either a microorganism outwits the immune system, or the immune system simply is not capable of dealing with an infection. An infection might be aggressive, spreading faster than the immune system can respond, or new, with the immune system not recognizing it as a threat until it has gained a foothold in the body.