Skip to 0 minutes and 14 seconds HEATHER LONG: Every day throughout our lives, we come in contact with millions of germs, such as bacteria and viruses, that have the potential to make us ill. These germs are called pathogens. However, mostly we don’t even realise we’ve encountered them, and that’s thanks to our amazing immune system. There are two main parts to our immune system. The first lines of defence are mostly physical and chemical barriers that you may not even have thought of as part of the immune system. So these include things like your skin, stomach acid, saliva, mucus, tears, and sweat. These all either prevent entry into the body, kill invading pathogens directly, or trap them for destruction.
Skip to 0 minutes and 51 seconds However, for any pathogens that get past these barriers, we have an internal network of dedicated tissue, cells, and organs that work together to protect the body. To function properly, the immune system must be able to detect a wide variety of foreign invaders and distinguish them from our own healthy body tissues. This requires careful coordination between a number of different types of white blood cell. The vast majority of blood cells are produced in the bone marrow, the soft fatty tissues inside the cavities of our larger bones. Within the bone marrow, all blood cells originate from a single type of cell, called a hematopoietic, or blood stem cell. These cells have the ability to make all the different types of blood cells.
Skip to 1 minute and 32 seconds When a blood stem cell divides, it can either become myeloid stem cell or a lymphoid stem cell. Myeloid stem cells go on to produce red blood cells, which transport oxygen to our tissues, platelets, which help our blood clot, and several types of white blood cells which are kind of rapid strike force, including monocytes and neutrophils. Alternatively, lymphoid stem cells produce several different types of lymphocytes, which are some of the most powerful cells in our immune system. And these include B-cells and T-cells. You will learn more about some of these cell types and their functions, and why they’re important to cancer immunotherapy during the course.
Skip to 2 minutes and 12 seconds Once our white blood cells are mature, the enter the bloodstream and begin to circulate around the body. Some white blood cells squeeze out through tiny gaps in the blood vessel walls and migrate through the body tissues, to check for infection or damage. They’re later collected in a series of vessels called the lymphatic system, which runs throughout the body in a similar way to blood vessels. Immune cells that travel along lymph vessels, collecting large numbers in specialised tissues that you may have heard of, called lymph nodes and the spleen. Here the immune cells exchange information and are activated to fight infection. You may have noticed that sometimes your lymph nodes or glands can swell when you have an infection.
Skip to 2 minutes and 50 seconds We can see some of our immune cells by taking a small volume of blood, spreading a drop on a slide, and staining it to look down the microscope. You will see straight away that there are lots of cells in the blood. In fact, each drop contains around five million red blood cells, and there are one to 200 red blood cells for every white blood cell. If we look at higher magnification, you can see some of the types of white blood cells. Here is a monocyte, one of the largest white blood cells, with a big nucleus. Here is a lymphocytes, which is a much smaller cell that also has a round nucleus.
Skip to 3 minutes and 24 seconds There are several different types of lymphocytes to perform different jobs. Here is a neutrophil which has a very different segmented nucleus and contains lots of toxic granules. In the laboratory, we can isolate the white blood cells from the blood by layering the blood onto a specialised dense sugary solution. The blood is then put into a centrifuge and spun at high speed for up to half an hour. This allows the red blood cells to fall through the sugary solution, but the white blood cells stay floating on top. We can then remove the white blood cells and study their function in the laboratory.
Blood under the microscope
In this short video, Dr Heather Long takes you into the laboratory to describe the components of the immune system and introduce some of the immune cells in the blood. We will look at some of the different white blood cells and the jobs they do for us in more detail in the next section.
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