Immunology in the TV3 Marathon

Basically the agents that act in any immune response are cells and molecules. All come from pluripotent stem cells that are found in the marrow of our bones, from where they are differentiated. They can be classified into innate immunity, and acquired immunity. The cells that make up the innate immune system are mainly leukocytes or white blood cells. Surely some of them will be familiar due to routine medical check-up: neutrophils, eosinophils, basophils… but there are also dendritic cells, mast cells and macrophages, outside the blood. We have also included the most important family of molecules: cytokines, which among other things control inflammation. The innate immune system is shared by practically all living beings, it is nonspecific, that is, it responds to any type of pathogen, like viruses, bacteria, fungi or protozoa. It is very fast, it activates in a matter of minutes or seconds, and it has no memory. On the other hand, we have the acquired immune system, which we only share with vertebrates. In contrast to the previous one, it is specific, therefore, it adapts to the type of pathogen that cause the infection. It is slower to activate (between 7 and 10 days), and generates memory. It is made up of fewer types of cells and they are less known: B and T lymphocytes, of which there are CD4 and CD8, and some well-known molecules, if only by name: immunoglobulins or antibodies, of which one type specifically, IgG has a characteristic Y-shape.
How the immune response works? We will help ourselves with a mass of slime, in which we have added iron filings. It has a whitish color because it represents some type of white blood cell. We will also use a powerful neodymium magnet that represents a pathogen, a virus, or a bacterium. When the white blood cell locates the particle, it begins to emit extensions of its cytoskeleton called “pseudopods”, which end up surrounding and capturing the particle. This process is called phagocytosis, and it is very important to neutralize extracellular pathogens, that is, those pathogens that circulate freely in the body. However, when the infection is too important and especially when the pathogens are intracellular, that is, when they are found within the cells of our body, this defensive system is not enough. This is the case of all viruses, which are strict parasites and multiply inside our cells, using our molecular machinery. Then, a particular type of phagocyte called a dendritic cell, expresses on its cell membrane fragments of the pathogen that it has just phagocytosed, and travels through the lymphatic system to a node where it stimulates T lymphocytes and then B lymphocytes. The B lymphocytes will make the specific antibodies for the antigen that the dendritic cell will have transported, while the T lymphocytes will be activated, doing their coordination function if they are CD4, and destroying our infected cells if they are CD8.
With a polystyrene ball we can represent a human cell infected by virus, and with a sponge, a CD8 T lymphocyte. When this lymphocyte detects the infected cell, it secretes a series of cytotoxic substances that basically pierce and destroy the cell by osmotic shock, enzymatic lysis and death-inducing signals.
Therefore, the two basic mechanisms of destruction of pathogens are phagocytosis when the infection is extracellular and cytotoxicity, when the infection is intracellular. The antibodies are specific and while they are maintained, they improve phagocytosis in future extracellular reinfections, while T and B lymphocytes also have memory and protect us from future intracellular reinfections, as occurs in COVID. The vaccine is based on stimulating the production of these types of memory cells