To defend against dangerous pathogens, the body’s second line of defense—adaptive immunity—is key. Although it might be slow to respond when compared to the body’s first line of defense (the innate immune system) the adaptive immune system is a complex system that focuses on precision and memory rather than speed.
Adaptive immunity is the reason why the body takes less time after the first exposure to recover from diseases like the common cold or the flu.
What Is Innate Immunity?
Innate immunity is acquired from one’s genetic makeup. The innate immune response can quickly protect the body against some viruses and bacteria but it can’t tell the difference between one virus or another.
It employs three different kinds of barriers:
- Physical barriers: Mucous membranes, earwax, and stomach acids
- Chemical barriers: Enzymes that kill pathogens which are found in sweat, mucus, tears, and saliva
- Cellular defenses: Natural killer cells, including macrophages, neutrophils, and dendritic cells
The purpose of the body’s innate immune response is to prevent the spread of pathogens throughout the body as quickly as possible. An example of this would be coughing. Since coughing propels air and particles from your lungs at speeds of up to 50 miles per hour, most germs, mucus, dust, and other potential threats are expelled before they can even enter the bloodstream.
If a threat does make its way to the bloodstream, the innate immune system first employs nonspecific cellular defenses such as natural killer cells that:
- Limit the spread of infection.
- Prevent further tissue damage to cuts or bruises.
- Kill cancerous cells and help control immune responses.
Natural killer cells can fend off most pathogens but are not as effective against specific invaders known as antigens or immunogens.
Adaptive Immunity: Vital Against Specific Invaders
Unlike innate immunity and its many non-specific defense mechanisms, adaptive immunity employs a class of white blood cells called lymphocytes that specialize in fighting off specific antigens and immunogens.
There are 2 types of lymphocytes:
- Regulatory T Cells: T cells bind and kill cancerous cells. They are direct fighters that secrete chemical messengers called cytokines that stimulate B cells to produce antibodies.
- B Cells: B cells determine the specific immune response and produce the antibodies that fight antigens.
It takes lymphocytes longer to react to pathogens at first because they must analyze a specific antigen and store it in their memory. Through a process called clonal expansion, the body produces millions of these antigen-specific lymphocytes and memorizes—for many years—how to combat several types of antigens.