Immune Cells: Types & Explanation

Instructor: Katie Chamberlain

Katie has a PhD in Microbiology and has experience preparing online education content in Biology and Earth Science.

The immune system is extremely complex. This lesson includes a rundown of the basic immune cells and what they do. There is a quiz at the end if you are feeling brave.

What Are Immune Cells?

An army is a force of people fighting together. The immune system is just like that, except it's a collection of cells fighting together. The immune cells are the soldiers that defend our bodies from invaders. Just like different soldiers have different jobs, so do different immune cells.

The immune system has two parts: innate and adaptive. Different immune cells play roles in each of them.

Cells of the Innate Immune System

The innate immune system is very general and includes the skin, mucus, and saliva. It also contains cells that travel around the body looking for things that are suspicious. Immune cells have receptors that allow them to detect certain things (like bacterial cell proteins and dsRNA) that are unique to bacteria, viruses, or fungi. In other words, they recognize non-human things.

Some immune cells find these things and then get rid of them by eating them! No joke! They ingest the sketchy invader in a process called phagocytosis and then break it down. One type of phagocytic cell is called a neutrophil. Neutrophils hang out in the blood and can get called to particular sites of infection. Another type of phagocytic cell is a macrophage. Macrophages can move here and there around the body, but they really like to hang out in the spleen and lymph nodes where they see a lot of action.

Natural Killer Cells are just what they sound like: tough, assassin-type cells. These guys look for problems within our own cells. If it looks like a cell has been hijacked by a virus or cancer, the natural killers move into action. However, they don't eat their prey. Instead, they release chemicals to get the job done.

Eosinophils are similar to Natural Killer Cells because they don't engulf their prey. These cells hang out near mucus membranes and look for things like parasites. They release enzymes to destroy any invaders.

Dendritic Cells are a link between the innate and the adaptive immune system. They are sentinels that look for fishy things near the skin. If they find something, they eat it, but then bring it to a lymph node and deliver it to the adaptive immune system.

Cells of the Adaptive Immune System

The adaptive side is very intricate and specific. The innate immune system can recognize bacteria, but it doesn't know bacteria A from bacteria B. The adaptive system, knows A from B and also knows if they've ever infected the body before. The main cells of the adaptive immune response are two types of white blood cells: B cells and T cells.

B cells develop in the bone marrow (think 'B' is for 'bone marrow'). Each B cell has a unique receptor on its surface that detects a bit of an invader called an antigen. There are millions of different possible B cell receptors.

When a B cell receptor meets its matching antigen, it becomes activated and begins to release a free-standing version of the receptor called an antibody. The antibodies then go out into the body and bind to any remaining invaders. It also creates a standing-militia of Memory B cells that recognize the same antigen. This way, if it invades again, the body will detect it very quickly.

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