Macrophages, antigens and the chemical messengers
Monocytes turn into macrophages when they are needed. A macrophage engulfs a pathogen and then shows its antigens on its own surface to the helper T cells. The helper T cell that fits this pathogen recognizes the antigen and is activated, and it then activates the B cells, to make antibodies, and the cytotoxic T cells, to kill infected cells. Antigens are proteins or glycoproteins on the surface or membrane of a pathogen. They differ from one organism to another, so they mark the pathogen as foreign. Several chemical messengers help the cells to work together. Chemokines guide the large phagocytes that circulate in the blood to the place where microbes are, to stop them multiplying and spreading. Interleukins carry messages between different immune cells; for example, activated helper T cells send interleukins to activate B cells. Complements are proteins and enzymes that destroy microbes in the blood after they have joined antibodies: they burst the membrane of the antigen and dissolve its contents, so phagocytes can swallow it easily. Interferons are proteins made by tissue cells infected with a virus. They are not specific to one virus. They bind to healthy cells next to the infected ones and make them produce enzymes that stop the virus copying its nucleic acid, so it cannot multiply and spread in the body.
| Messenger | Made by | Job |
|---|---|---|
| Chemokines | immune system cells | guide large phagocytes to the microbes |
| Interleukins | immune cells such as activated helper T cells | carry messages that activate other immune cells, such as B cells |
| Complements | proteins and enzymes of the blood | after joining antibodies, burst the antigen’s membrane so phagocytes can swallow it |
| Interferons | tissue cells infected by a virus | make healthy neighbours stop the virus copying its nucleic acid |
| Situation | Messenger |
|---|---|
| Large phagocytes must be guided to a place with microbes | chemokines |
| A helper T cell must activate a B cell | interleukins |
| The membrane of a microbe joined by antibodies must be burst | complements |
| Healthy cells next to a virus-infected cell must stop the virus copying | interferons |
Message chain game, with a grown-up. Write the roles macrophage, helper T cell, B cell and cytotoxic T cell on four cards, and the messages “shows antigen”, “interleukin” and “activates” on three more. Act the steps in order, with one person for each role passing the message cards on. Then swap roles and repeat, and say what would go wrong if the helper T cell never received the antigen.