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Skip to 0 minutes and 13 secondsINSTRUCTOR: In the blood film, we saw a monocyte, one of the biggest white blood cells. When these cells leave the bloodstream and go into our tissues, they become macrophages. You can find them in the lungs, liver, skin, and gut. If you become infected with a pathogen, such as a type of bacteria, your macrophages can find them and swallow them whole. They then use their toxic granules to destroy the bacteria.

Skip to 0 minutes and 47 secondsAnother type of white blood cell that is immediately ready to fight infection is the neutrophil. These cells are packed full of toxic granules. Neutrophils are present in high numbers in the blood and are rapidly recruited to the site of infection. They can release their toxic granules to kill bacteria.

Skip to 1 minute and 10 secondsNatural killer, or NK cells, can also respond quickly. They have receptors on the surface called NK receptors. When body cells become stressed-- for example, when they're infected with a virus-- they display molecules on their surface that act as stress signals, alerting the immune system that something is wrong. Natural killer cells can recognise these stress signals and kill the stressor cells.

Skip to 1 minute and 38 secondsAnother important type of white blood cell is the dendritic cell. This name comes from the Greek word dendron, which means tree, because of all it arms which reach out like branches. The dendritic cell is really important for communication between white blood cells.

Skip to 1 minute and 56 secondsDendritic cells are good at recognising and taking up pathogens or foreign proteins.

Skip to 2 minutes and 4 secondsInside the dendritic cell, these all digested into small pieces. Some of these small pieces stick to celluar proteins called MHC molecules. These take the foreign proteins to the cell surface and display it to other immune cells. The dendritic cells travel to lymph nodes to stimulate immune cells that are able to recognise the invading pathogen. The smallest type of white blood cells we saw down the microscope are called lymphocytes. These can measure less than 1/100 of a millimetre. Although they all look the same down the microscope, there are several different types of lymphocytes. These include B cells and two types of T cells-- cytotoxic T cells and helper T cells.

Skip to 2 minutes and 54 secondsT cells all have a special receptor on their surface called a T cell receptor, or TCR for short. In the lymph nodes, T cells use their receptor to scan the dendritic cells for any pieces of foreign proteins displayed by their MHC molecules. The dendritic cells then activate the T cells and give them information on how to find the pathogens.

Skip to 3 minutes and 19 secondsHelper T cells' main role is coordinating immune response, giving instructions to other types of immune cells.

Skip to 3 minutes and 28 secondsThe main job of cytotoxic T cells is to seek out infected cells displaying the same foreign protein on their MHC molecules and to kill them.

Skip to 3 minutes and 42 secondsThe other type of lymphocytes, B cells, also have specialised receptors on their surface, this time called B cell receptors. Ultimately, B cells that recognise foreign proteins or pathogens, such as bacteria, start making these in a form that can be released from the cell. These are called antibodies, and they can stick to the invading pathogens, stopping them in their tracks and marking them for destruction. B cells can also make antibodies that can stick to infected cells.

Immune cells and their roles

The immune system involves coordination of several different types of white blood cells that all have different jobs in the fight against infection.

Your task: watch this video animation in which PhD student, Benjamin Meckiff, describes some of our different white blood cells and their functions in the immune response. Some of the cells he mentions will feature later in the course. You will be able to test your knowledge in the ImmuneSmart Cell Challenge game in the next section.

Reflect on any new information or ideas and share your thoughts with other learners in the comments area.

For those who would like more information about how the immune system works, check out these summaries on the Patient website, and IMGT website.

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This video is from the free online course:

Cancer Immunotherapy: a Step Change in Cancer Treatment

University of Birmingham