Amanda has taught high school science for over 10 years. They have a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. They also are certified in secondary special education, biology, and physics in Massachusetts.
What Is an Immune Response?
Remember having a cold? The stuffy nose, sore throat, and cough can put a real damper on your weekend activities. Have you ever stopped to think what happens in your body while you're sick? Although you might feel terrible at first, your immune system, a collection of cells and tissues, works day and night to defend your body. Your immune system is made of a variety of immune cells. Macrophages are general soldiers. They patrol your body, looking for invaders to engulf and destroy. Leukocytes are specialists and adapt to a specific pathogen. B-cells make antibodies, T-cells directly attack pathogens, and natural killer (NK) cells attack infected cells.
Like an army, these cells need to talk to each other to coordinate an immune response or an attack on the invading pathogen. However, your cells don't have walkie-talkies like soldiers. They use two main types of communication to mount their response, chemical communication and direct cell-to-cell communication. Let's look at how these types of communication work in detail next.
The main chemicals of the immune system are called cytokines. Immune cells make these chemicals and send them out into the body to activate and recruit other immune cells. Cytokines are like a message saying, ''Hey, there's an infection. We need your help!''
Cytokines spread through the body and attach to the surface of other immune cells at proteins called receptors. The receptors signal the cell to change what proteins it makes and its behavior to help fight the infection. There are hundreds of cytokines in the body, which can be divided into four main categories: interleukins, interferons, chemokines and tumor necrosis factors.
Interleukins allow for communication between leukocytes. Interleukins are used to activate T-cells and B-cells, snapping them into action for the battle. They also increase the production of lymphocytes, which increases the immune response. You can think of this effect as recruitment in the army. When there is a war, recruitment increases, making a bigger army to fight the enemy.
Like other cytokines, there are several types of interferons. However, all interferons are secreted in response to a viral infection. Interferon-I is made by nearly all cells in the presence of a virus, but interferon-II is made specifically by NK cells and T-cells. Interferons cause infected cells to fight the virus more efficiently and activate T-cells and NK cells to attack.
Picture cooking a delicious dinner. The smells from the kitchen might attract quite a few people in your house. Perhaps surprisingly, your immune system uses a similar strategy to attract lymphocytes to the site of infection. Macrophages and other immune cells secrete chemicals called chemokines. These chemicals act as a chemical attractant, bringing immune cells to the area just like the smell of food brings all your siblings to the kitchen.
Tumor Necrosis Factors
During an infection, tumor necrosis factors are secreted by macrophages, B-cells, T-cells, and natural killer cells (NK). This cytokine induces an inflammatory response, increasing blood flow and recruiting white blood cells to the area. It is also involved in cell self-destruction during an infection.
Chemical communication is like sending long distance messages between soldiers. Cell-to-cell communication is more like a special-ops unit, where members communicate intimately on a mission.
All pathogens have antigens, or parts on them that alert the immune system they are an invader. Some cells in the body can capture these antigens and display them on their surface in receptors. The receptors and antigens then can bind to other immune cells, activating them and showing them exactly what to look for. These cells are called antigen-presenting cells. Several cells do this including macrophages.
Macrophages engulf and destroy pathogens. When they do this, they save some of the antigens and present them on their surface in receptors. These receptors bind directly to other immune cells, including helper T-cells. The helper T-cells then help activate the rest of the immune system, hence their name, by sending chemical signals to other T-cells and B-cells.
Cytotoxic T-cells also use direct cell-to-cell communication but for a different purpose. When a cell is infected with a pathogen, it presents the antigens on the surface to let the immune system know it is infected. Cytotoxic T-cells recognize these antigens with their own receptor proteins. They then tell the cells to undergo programmed cell death and destroy themselves. Although it might seem bad to kill host cells, the body does this for the greater good to prevent the infection from spreading.
The immune system is made of lymphocytes that need to communicate to fight an infection. Cytokines allow for long-distance communication between leukocytes (T-cells, B-cells, and NK cells) and other white blood cells like macrophages. Interleukins, interferons, chemokines, and tumor necrosis factors all help activate the immune system and recruit lymphocytes. Lymphocytes also use cell-to-cell communication. Antigen-presenting cells show other immune cells antigens from pathogens to activate a specific immune response. Cytotoxic T-cells find antigens presented on the surface of infected cells for destruction.
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