Your body is equipped with the capability to heal itself: the immune system and its corresponding immune system cells. In the span of a day, your body encounters a slew of pathogens: from viruses to bacteria, to parasitic worms, all taken care of by the body’s layered smart defense system — the immune system cells. In this article, we’ll list down all the immune system cells and talk about the corresponding roles they play in maintaining your overall wellbeing.
Immune System Cells And Their Innate Functions
1. Dendritic Cells
Mostly found in the parts of the body that integrates with internal and external environments like the skin, stomach, and lungs, dendritic cells are the sentinels of the immune system. They move around, constantly checking their surroundings, ingesting antigens (a foreign substance capable of inducing a response from the body’s immune system).
After ingestion, they take themselves to the lymph nodes to allow for a more adaptive immune response from the T Cells. Dendritic cells are a part of the body’s first line of defense against threats: the innate immune system. They can identify threats and act as messengers for the rest of the immune system through antigen-presenting cells. Dendritic cells also act as the bridge between the innate immunity and the adaptive immunity of the body.
2. Innate Lymphoid Cells (ILC)
These newly-discovered immune lymphoid cells lack antigen-specific T or B receptors. They play an important role in the body’s response against helminthic infections and can recognize distressed cells in the absence of antibodies. ILCs discharge high concentrations of cytokines and are embroiled in inflammation, innate immunity, tissue remodeling, and lymphoid tissues formation. ILCs are very consistent in their part in immunity surveillance. They are also responsible for early recognition of pathogens.
Their population is extensive, they’re being found all over the body and enhanced in mucosal surfaces. These cells are able to communicate with different immune system cell types to integrate the immune system during inflammation and homeostasis.
3. T Cells
T cells are a type of white blood cell that plays a significant role in immunity. These cells work with macrophages. T cells scan the body for pathogens and eradicate infected cells (including cancer cells). They also activate other cells that ingest germs and assist other cells in the creation of antibodies. As a part of the body’s adaptive immune response, T cells also have the capability to “remember” pathogens they have encountered years ago.
However, unlike macrophages that can fight any virus or invading cells, each T-cell can only attack one type of virus. T-cells are like special defense unit that stops only one kind of virus that can be harmful to the body.
They can be classified into two categories:
- Cytotoxic T cells — also known as “killer” T cells, and aptly so. Cytotoxic T cells search and kill infected cells that have been transformed into virus-making machines. To do this, killer t-cells need to identify the difference between the healthy cells and infected cells with the help of special molecules called antigens.
- Helper T cells — These type of t-cells doesn’t get rid of any invaders nor create toxins. Instead, helper t-cells are like coordinators. They use special chemical messages to provide directions to the other immune system cells. These directions aid B cells and killer T cells to multiply immensely so they can get rid of the invaders and make sure the battle stays under their control. Helper T cells also assist in the maturation of B cells and memory B cells.
4. Natural Killer (NK) Cells
Natural killer cells are a type of lymphocytes (a white blood cell) and a member of the innate immune system that exhibit cytotoxic properties. They play a huge role in the body’s response against both viral-infected cells and tumors.
NK cells activation triggers in response to macrophage or interferons derived cytokines. Their purpose is to control viral infections while the adaptive immune response is creating antigen — a specific T cells that can get rid of the infection.
A person with a deficiency in NK cells is confirmed to be highly vulnerable to early stages of herpes virus infection.
5. Myeloid-derived Suppressor Cells (MDSC)
Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of cells characterized by their myeloid origin, macrophages, immature granulocytes, and dendritic cells at different phases of separation. They expand during infection, inflammation, and even cancer. They are the body’s natural immunosuppressant: they regulate the T cell, dendritic cell, and macrophages’ functions.
Studies on therapeutic strategies are currently being developed to use MDSCs to inhibit immune responses in the condition of autoimmune disease or to advance anti-tumor immune responses.
Platelets are produced in the bone marrow, just like red cells and most of the white blood cells. They develop from mature megakaryocytes in the response of thrombopoietin (TPO). Though they’re not actually a true cell but mere cell fragments, they contain many forms that play a vital role to stop bleeding. Platelet has proteins on their surface that allow them to bind together. In cases of blood vessel damage, platelets rush in to stop the bleeding and adhere to the damaged blood vessel wall and also send out a signal for more platelets to come in and rush to the problem site. They are the blood cells responsible for clotting.
The normal platelet count in a person is around 150,000 to 450,000 per microliter of blood. Low platelet count increases bleeding vulnerability while high platelet count may cause stroke.
7. Red Blood Cells (RBCs)
Red blood cells, also known as erythrocytes, are the most prolific immune system cell type in the blood. They develop from the stem cells in the red bone marrow or in the fetal liver. RBCs have a unique structure that looks like a flexible disc shape.
Though the RBC’s main function is to deliver oxygen to the various parts of the body, they also provide a barrier against infections, blood parasites, and bacteria. They also have the ability to advance vasodilation by discharging adenosine triphosphate (ATP) when under the condition of profound stress and initiate an immune response when they are lysed by pathogens. New research also shows that RBCs also modulates the immune system response.
Thymocytes are blank cells developed in the thymus. They undergo several phases of selection and extreme quality control to make sure maturation results in functional T cells. This pool of T cells can respond effectively to foreign pathogens. Thymocytes mature into T cells through thymopoiesis.
9. B Cells
B cells are also a type of white blood cell that is part of the immune system and develops from stem cells in the bone marrow. They contain a receptor protein called B cell receptors, which allows them to bind to an antigen, and initiate a specific response.
While T cells destroy the body’s own infected cells or have become cancerous, B lymphocytes create antibodies to counter the invading viruses, bacteria, and toxins.
Granulocytes are another type of white blood cell. They are called granulocytes because of the granules present in their cytoplasms, which they release during infections and allergic reactions. There are three types of granulocytes:
- Neutrophils – ingests microorganisms, releases enzymes to kill it
- Eosinophils – regulate immune cell functions; involved in the eradication of tumor cells and repair of damaged tissue
- Basophils – releases histamine when damaged, contributing to the body’s inflammatory response
Basically a bone marrow cell, essential for blood clotting. Megakaryocytes are 10 to 15 times bigger than the typical RBC.
Monocytes are also a type of white blood cell. They play a role in adaptive immunity, as they can differentiate into macrophages (which engulfs and digests pathogens) and dendritic cells.
Download, save or share this infographic for reference: Immune System Cells and their Functions.
Check out this video from Stem Cell Researchers for the types of immune system cells and their functions:
The immune system is our first line of defense against diseases. Knowing how it works is an important part of keeping it in tip-top shape.
How do you fortify your immune system? Share your tips in the comments section below.
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Editor’s Note – This post was originally published on November 1, 2017 and has been updated for quality and relevancy.