This lesson is on specific and non-specific immunity. Here, we’ll go over what your immune system is and what it does. We will also explain the two parts of the immune system, specific and non-specific.
What is the Immune System?
You wake up and you’re not feeling well. Maybe your throat hurts, and you have a bit of a headache. It seems like a pathogen, or infectious particle, has breached your immune system! Your immune system is a group of tissues, cells, and chemicals inside your body designed to protect you from illness. Illnesses are caused by pathogens, which are viruses, bacteria, and parasites. There are two main parts to your immune system: the non-specific and specific immune systems. Let’s talk about the non-specific immune system first.
Your defense system starts with non-specific immunity, also known as innate immunity. This system is comprised of general mechanisms your body deploys every day to keep you safe. They are always working in the background, no matter what pathogens you are exposed to. They don’t discriminate who they fight!
There are many types of non-specific immunity. One of the largest examples is your skin, which forms a tough, mechanical barrier that serves as the initial barrier to keep pathogens out. Your skin cells actually secrete small proteins that destroy viruses as well. Other barriers to pathogens include: small hairs inside your lungs that filter out bacteria inside mucus, the acid your stomach secretes to break down food and any pathogens that enter through your food, and specialized lining in delicate body parts, like your lungs. Below is a micrograph taken of cilia lining the tissue in your lungs.
There are also specialized immune cells that fight intruders once inside the body. The first type of cell is a macrophage, which patrols the body through your blood. When an invader enters, the macrophages move into the tissue like soldiers and remove the threat by swallowing the pathogen and digesting it in a process called phagocytosis, as shown below.
Basophils are cells that secrete chemicals called histamines, which call more immune cells to the scene. T-cells are a type of immune cell that works in both the non-specific and specific immune system. There are three types of T-cells, helper T-cells, cytotoxic T-cells and natural killer T-cells. Only natural killer T-cells are part of the non-specific immune system.
Natural killer T-cells find and destroy pathogens in the body. They look for cells that do not resemble host cells and destroy them by releasing chemicals that cause the pathogen to break down. They do this to all foreign cells, not specific ones, so they belong in the non-specific immune system.
Specific immunity, also known as adaptive immunity, is specialized immunity for particular pathogens. Helper T-cells, cytotoxic T-cells, and B-cells are involved in specific immunity. The non-specific cells, like macrophages, tell the T- and B-cells that an intruder is present. The macrophages show the T- and B-cells parts of the pathogen, called antigens, so they know what to look for. Later, a special kind of cell called a memory cell creates a record of which intruders entered the body, so they can attack it faster during the next infection.
There are two types of specific T-cells: helper T-cells and cytotoxic T-cells. Helper T-cells recognize antigens from the macrophages and help to organize other cells in the immune system for a fight.
Cytotoxic T-cells recognize infected cells and kill them before the infection spreads. They are like assassins, going in to kill the infected cells for the greater good. Even though the infected cells of the host die, the infection is contained, and damage is minimized. In this image, a host cell is letting a cytotoxic T-cell know it is infected by showing it the pathogen’s antigen on the surface. The cytotoxic T-cell will then attach and destroy it.
B-cells make a special protein called an antibody. Antibodies are proteins that are extremely specific for one particular invader. The B-cells have antibodies on their surface to recognize the pathogen, and they secrete antibodies into the blood. The antibodies circulate the body, attaching to pathogens and disabling them until macrophages can come by and digest them.
These cells are specific to an individual pathogen. Every time you encounter a new pathogen, your body must mount another specific response and create new B-cells. This is a lot of work, but often your body runs into the same invader more than once. When it does, the immune system is ready. A few special cells called, memory B- and T-cells, stick around after the initial battle is over. If the same pathogen comes around again, the memory B- and T-cells are activated and can respond quickly. In other words, memory B- and T-cells memorize the original pathogen so they can respond faster the next time.
Vaccines are a clever way humans have used the immune system to prevent the spread of the disease. Vaccines inject a small antigen, or in some cases a small dose of a live pathogen, into a person. This evades most of the non-specific immune system by injecting it directly into the blood. The B- and T-cells are activated, and memory cells are created without significant risk of a serious infection. The next time the person encounters that pathogen, the B- and T-cells can fight it off with little or no damage to the body. Smallpox, for example, has been almost entirely eradicated due to vaccination policies.
The non-specific immune system involves defenses that are general and ongoing. Skin, parts of the lungs, and stomach are mechanical barriers. After the pathogen enters the body, non-specific cells like macrophages attack and ingest the pathogens, and natural killer T-cells attack the pathogen directly. Macrophages present antigens to the specific immune system, made of B- and T-cells. Helper T-cells alert other parts of the immune system and cytotoxic T-cells kill infected host cells. B-cells make antibodies that disable pathogens until they can be killed by macrophages. After an infection, memory B- and T-cells stick around to prevent infection from the same pathogen in the future. This process is why vaccines can be effective.
Immune System Vocabulary ; Definitions
- Immune system: A group of tissues, cells, and chemicals inside the body designed to protect the body from illness
- Pathogens: Viruses, bacteria, and parasites that cause illnesses
- Non-specific immunity: A system that is comprised of general mechanisms to keep the body safe; also known as innate immunity
- Specific immunity: A specialized immunity for particular pathogens; also known ad adaptive immunity
At the end of the video, set a goal to do the following:
- Explain what the immune system is
- Differentiate between non-specific immunity and specific immunity
- Discuss the impact of vaccines on immunity