What is immunity or Immune System? Why does the human body need immunity?
The word immunity comes from the Latin "immunitas", which means the body's ability to fight disease. The operation mechanism of the Immune System is very sophisticated. Its main function is to protect the body from foreign microorganisms, viruses, bacteria, fungi, parasites, allergens, carcinogens and atrophic cells. When the human Immune System is functioning normally, the body organs are protected, effectively resisting the above-mentioned possible pathogenic factors, and maintaining the state balance in the body.
Immunology can be regarded as a branch of basic biology, and it is also an extremely important subject in basic medicine. think about it! How does the research organism deal with the invasion of foreign enemies? Ordinary people, if we have a deeper understanding of this knowledge, we will be able to prevent diseases and maintain health, and even prevent about 40% of cancers! I hope to use the space of 3,000 words to let you understand this somewhat mysterious knowledge.
Summary - Following aspects are covered by this post:-
- Definition of Immune System
- 7 Components of Immune System
- Body Infection and Human Defence System
- Fever is the result of Immune System Response
- How the body know among the friends and foe
- T-Cells and B-Cells are human body Trained Army
Components/ Parts of the Immune System
- White blood cells. White blood cells are the main part of immune system. White Blood cells are made in bone marrow of human body. White blood cells move in blood and tissue for searching of microbes such as bacteria, viruses, parasites and fungi. When they locate them, they launch an immune attack.
- Antibodies. Antibodies are proteins that protect human body when an undesirable substance enters the body. Antibodies are produced by immune system and responsisble to remove undesirable substances from humna body.
- Complement system. The complement system is a group of proteins and it provide support to immune system to fight against human body infection, heal up injury and kill dangerous bacteria and viruses.
- Lymphatic Sytem. Keeps body fluid levels in balance state and defends the human body against infections.
- Spleen. The spleen is a small organ inside human body left rib cage and above the stomach. Spleen is part of the lymphatic system and it is part of the immune system. The spleen stores and filters blood and makes white blood cells that protect from infection.
- Bone Marrow. The soft, spongy tissue with many blood vessels and found in the center of most bones of human body. There are two types of bone marrow: red and yellow. Red bone marrow contains blood stem cells that can become red blood cells, white blood cells/ platelets.
- Thymus. Thymus is a small gland in the lymphatic system that makes and trains T-cells (special white blood cells). The T-cells help immune system to fight against disease and infection.
Animals’ first line of defense against pathogens is physical barriers such as skin, epithelial tissue, and mucous membranes. Tears can wash the cornea and remove attached bacteria; ciliated cells that breathe in the mucous membrane constantly vibrate their cilia to remove mucus and attached foreign body. In addition to barrier and cleaning functions, these places also have chemical weapons, such as tears, saliva, and lysozyme in the mucous membranes, which can dissolve the cell walls of bacteria; the oil glands of the skin secrete fatty acids, which can kill bacteria; salt in sweat is also produced on the skin High-salt environment prevents the growth of various bacteria.
The second line of defense is the so-called "innate immunity", that is, there are already some receptor molecules on the surface of some cells, which can recognize certain surface molecules of the old enemy. Once the two molecules join, they can send signals to the nucleus and activate many genes. Activate its defense function, such as increasing phagocytosis, which can swallow bacteria or viruses and digest them; it can also secrete small molecules (such as chemokines, cytokines) to call similar phagocytic cells to help fight, Or induce inflammation in a small area, increase the permeability of blood vessels in this area, and blood plasma penetrate into the tissue, causing redness, swelling, heat and pain, and attracting various immune cells to work together to eliminate pathogenic organisms.
Immune Sytem response against any infection is result into Fever
A rise in body temperature/ fever, can happen due to human body infections or it is surely an immune system response. A rise in temperature can kill some microbes and Fever also additionally triggers the body's repair process.
Who is the enemy? Who is one of us?
Antigen
Recognizing and treating self molecules and enemy molecules differently is not only the key to innate immunity, but also the ability of the entire Immune System. If we want to understand the complicated immunology, we should naturally master it. However, immune cells may encounter thousands of macromolecules as they travel around the body. How can they distinguish between friend and foe?
For cells involved in innate immunity, there are already genes encoding receptor molecules in their genomes. These genes are magic weapons for fighting enemies evolved by organisms for hundreds of millions of years after resisting the attacks of pathogenic organisms generation after generation. As long as it is expressed outside the cell, it can recognize foreign enemies and activate functions such as phagocytosis.
But can't pathogenic organisms counter it? Why not change the outer molecular shape to avoid being recognized? It turns out that receptor molecules (now called pattern-recognition molecules) can specifically recognize structural macromolecules that are difficult for pathogenic organisms to give up, such as the trust-like receptor ( Toll-like receptors, TLRs), one of the more than ten kinds of molecules (TLR-4) indirectly recognizes the important molecule lipopolysaccharide on the surface of Gram-negative bacteria. Bacteria cannot survive without this molecule, so in the long-term evolutionary struggle process . Based on this alone, assuming we favor animals, we can say that "the devil is one foot tall, and the Tao is one foot tall."
How to distinguish among different kindes of enemies?
The innate immunity acts very quickly. When a foreign enemy invades, it will launch a defense no later than four hours. However, if it cannot resist, it will rely on the chemical signals it sends to activate the next layer of defense system, which is called "adaptive immunity". .
In order to take over the retreating front, this system needs to recognize the foreign enemy more accurately. This task cannot be accomplished by dozens of receptor molecules, but must distinguish the very special surface molecules of the foreign enemy. This means that it must be able to recognize Over a million molecular surface shapes.
think about it! A system must not only know that hundreds of thousands of molecular shapes belong to itself, but also recognize that millions of molecular shapes belong to foreign enemies and can be attacked. This is impossible for a person with extremely high talent and intelligence. Where is the memory of dozens of blood and lymphocyte systems in animals? Where are its nerves? Where is its mind? How to be able to recognize, remember, and launch attacks?
Being able to unravel this big secret is a major achievement accumulated by immunologists since 1960. It turns out that in the process of biological evolution, permutations and combinations were invented, which split the receptor molecule into several parts, such as the variable region (V region), the junction region (J region) and the invariant region (C region), each of which is There are many variants. When immune cells divide and differentiate, the hundreds of genes arranged on the genome can be randomly combined to produce millions of different receptor molecules for selection.
We have just explained how the adaptive Immune System produces a wide variety of receptor molecules, and these nascent molecules are, of course, placed on the surface of cells in order to reach possible foreign enemies. Now we call the surface of chemical molecules that receptors can engage with as antigens, that is, the source molecules that can produce antibodies. And if the receptor molecule can break away from the cell surface and freely dissolve in blood, lymph or mucus, it can act like a guided missile to specifically deal with antigen molecules on pathogenic organisms. This protein macromolecule is called an antibody. . The method of using antibodies to deal with foreign pathogens is called "humoral immunity", which means that the immune cells are not directly involved, and the antibodies play the leading role in the attack.
Antibodies have high affinity for antigens, and bind to toxic foreign molecules to neutralize them, that is, to counteract their toxicity. If they bind to the surface of bacteria, they can help macrophages swallow bacteria. This is called opsonization, and can also attract bacteria. The complement system in the blood (nine proteins in the blood) comes to punch holes in the cell membranes of bacteria, bad cells or parasites, allowing them to die.
T Cells and B Cells are well trained Armies
There are two branches of the adaptive Immune System, one of which is called the B cell system. B originally refers to the chicken's Bursa of Fabricius, because if the bursa is cut off, the chicken's Immune System will not be able to produce antibodies. Although mammals do not have this structure, they are also called B (bone marrow) cells, because bone marrow is not only the place where the hematopoietic system produces various blood cells and lymphocytes, but also the place where immature B cells are negatively selected.
As mentioned before, the most important issue in immunology is how to distinguish oneself from the enemy. We know that natural selection is the environment's selection of different individuals in the group, and those with better fitness are retained, and the evolution of the immune system has also invented positive and negative selection. Cells that receive the receptor molecule undergo elimination and proliferation.
Immature B cells are in the bone marrow and will encounter various molecules of their own body. At this time, they will initiate suicide or modify instructions, so that the cells that deal with their own molecules will die or lose their ability to work. The remaining ones will only recognize foreign antigens.
The other branch of adaptive immunity is called T cells, because they have to go to the thymus for positive and negative selection. These cells have surface receptor molecules, but do not secrete them as soluble antibodies. So how do T cells defend against foreign enemies? In fact, once T cells are activated by foreign antigens, they will go into battle naked and participate in it personally, so it is also called cellular immunity.
T cells can secrete signaling molecules (such as lymphokine or chemokine) to stimulate B cells that can recognize the same antigen to multiply and produce antibodies, which are called helper T cells (helper T cells); if T cells directly It secretes enzymes to attack cancer cells or body cells infected by viruses, which are called killer T cells.
T and B cells that have undergone negative selection (that is, cells that eliminate self-antigens) will enter the lymph nodes of the lymphatic system and other places that are prone to encounter pathogens. When encountering antigen-presenting cells (dendritic cells, macrophages, etc.), the foreign enemy antigen it presents happens to be recognized by receptor molecules on the surface of T or B cells. This coincident encounter will greatly stimulate T or B cells , let it divide and multiply into a group, and start to work, or secrete antibodies, or attack cancer cells. This process is called positive selection, that is, to expand the team of selected T or B cells, and let it change from a single soldier to an army.
We all know that if a ballistic missile with a nuclear warhead is launched to attack some nuclear-armed countries, it will mean the tragic death of all mankind. Therefore, the box that opens the launch button has three locks, and three keys must be inserted at the same time to open the box, and the keys are kept by different people.
In the same way, when antigen-presenting cells want to activate T cells, they also need two pairs of locks and keys, one of which is the antigen receptor of T cells and the antigen complex (antigen and MHC class II molecules) on the surface of the other cell; One pair is the CD28 molecule on the surface of the T cell and the B7 molecule on the opposing cell. Both pairs of locks and keys can cooperate to transmit signals and activate T cells.
But if the activation signal is too strong, it will create more legions than needed, and it will also cause diseases. Therefore, there must be a negative feedback mechanism to reduce the degree of activation. How can this be done? There is an "immune checkpoint" hypothesis, that is, after T cell activation, another surface molecule (killer T cell surface antigen No. 4, CTLA-4) will be enhanced, and the affinity of this molecule to B7 molecules is much higher than that of CD28 molecules. Can replace it, and then extinguish the original activation state.
Using Immunity to Treat Cancer
The PD-1 receptor discovered by Tasuke Honjo of Kyoto University in 1992 and the CTLA-4 discovered by Allison of Texas University in 1995 are both inhibitory T cell surface molecules that can reduce the anti-tumor activity of T cells. Can an antibody that specifically binds to this inhibitory molecule make T cells more active and attack cancer cells in the body? Following this line of thought, Allison's team produced an antibody (ipilimumab), conducted three phases of clinical trials, and found some effects on metastatic melanocytic carcinoma. For example, about 23% of patients lived for more than four years, making the US Food And the Drug Inspection Agency in March 2011, approved the use of this drug. In the anti-PD-1 antibody test, 6~17% of the patients improved slightly, so if we understand the operation of the Immune System, we can regulate it so that it can attack foreign enemies or cancer cells hard, and the two of them won the first prize. Tang Award.
Immunology has a variety of applications, but could it be used to treat cancer? For a long time, experts have always believed that since a patient has cancer, the cancer cells should have escaped the supervision of the Immune System, so enhancing immunity is ineffective against cancer.
But as early as the end of the nineteenth century, there was a Dr. Cooley who used the mixed bacteria that had been killed as a vaccine for cancer patients to treat cancer. People tried it from 1893 to 1963, but the results were mixed. It was recognized by the medical authorities, and later someone used BCG to prevent the recurrence of bladder cancer. BCG is the killed Mycobacterium tuberculosis, and it is widely used as a tuberculosis vaccine. Since the late 1980s, after cytokinin was mass-produced by genetic engineering technology, interleukin II was effective against melanoma and kidney cancer, and finally persuaded those in power to admit that immunization can be used as one of the cancer treatments.
At present, there are four major directions in the treatment of cancer with immune methods. In addition to the above-mentioned "checkpoint suppression" strategy, there are also "cancer vaccines", "stimulation and activation of T cells" and "transplantation of foreign activated T cells (Tumor-infiltrating lymphocytes, TIL)" and so on.
Conclusion About Immune System
What are Types of Immune System
Innate immune system vs Acquired immune system
The human immune system can be divided into two parts, namely the "innate immune system" and the "acquired immune system".
The innate immune system is the first line of defense for human health. It is an innate resistance and a comprehensive protection mechanism. The innate immune system includes white blood cells, which can engulf and kill pathogens when the body is invaded by pathogens. In addition, the innate immune system also includes other important lines of defense, such as the skin barrier and mucus in the respiratory tract.
The Acquired immune system is specific. When the innate immune system fails to completely clear the pathogen, resulting in an infection in the body, the body will then produce antibodies and antigens. The acquired immune system will memorize these antigens and play the role of the second line of defense the next time it is invaded by the same pathogen. However, the acquired immune system does not produce an immune response immediately, on the contrary it takes a period of time to be activated. Therefore, the proper functioning of the innate immune system, which produces antibodies to fight disease as the first line of defense, is very important.
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