Welcome! The aim of this website is to help people understand basic concepts of immune system. On each part of this website you can read about different topics related to the immune system. These topics are selected to help you have some ideas about how immune system works and why it is important. You can go through the topics in-order or jump to any part you like.
What is immune system? Immune system defends human and other animals from diseases. There are countless microorganisms around us. They are invisible to naked eyes. These microorganisms, such as bacteria and virus, cause infectious diseases. The immune system is a series of collaborating physiological mechanisms. It is the key to human survival.
How does immune system work? Let us take the immune system as a security agent to our body. There are cells in our body, which have evolved to specialize in defense. As Invasion of microorganisms happens every second, let us think of “health” as a status during which our immune system suppresses infections. Sometimes, you feel sick because the growing of microorganisms overwhelms the immune system. If an infection is not controlled, even a minor cut can eventually be fetal. When the infection is too strong or the immune system is too weak, the immune system fails. Under such circumstances, the help of medication is required.
To make things short, there are three features of the immune system you need to know. They can help you understand many discussions related to modern medicine: 1. Immune system is crucial to survival 2. Immune system grows stronger over time. 3. Immunity provides future protection.
Why should we learn about immune system? People tend to understand health issues with their own experiences or what they believes to be true. Most of these knowledge lacks scientific evidence. The study of immune system builds upon the experiences of medical practices. Numbers of modern medications and treatments are developed with immunological studies. Knowing more of the immune system can help you understand many health related topics better. It can also help you with medical choices. For example, whether or not to get a vaccine.
Immune cells & pathogens Before we continue to discuss how the immune system develops, let us talk briefly about immune cells and disease-causing microorganisms. You must have heard of white blood cells. However, do you know there are different kinds of them? Leukocytes, which commonly known as white blood cells, derive from pluripotent hematopoietic stem cells. We will only talk about two of the most important kinds. They are B cell and T cell. B cell derives plasma cell and memory cell. T cell derives helper T cell and cytotoxic T cell. Microorganisms which cause diseases are called pathogens. They are four kinds of them: bacteria, viruses, fungi and parasites.
Innate immunity & adaptive immunity There are two types of immunity: innate immunity and adaptive immunity. Innate immunity responds to infection first. It reacts fast to infection. However, the innate immunity treats all the infections the same way. It provides fundamental defense. When the innate immunity is not sufficient to stop the infection, adaptive immunity steps in. The adaptive immunity comes up with solutions to target different infections specifically. It is more powerful than the innate immunity. Because the mechanisms are more complicated, it takes longer to show the effect. However, the adaptive immunity maintains memories of infections. Next time it can react much faster towards pathogen which it is previously exposed to. This is the key to long-term immunity. The Long-term immunity is utilized by scientists to create vaccines.
Immunity & vaccination
What is vaccine? How does it protect us from disease? The purpose of vaccine is to prevent disease. But how dose it work? The most basic idea is that the immunity is adaptive. In the early days, people found that some of those who survived from epidemic disease won't catch the same disease again. They are "immune" to the disease. This observation brings up study of human immune system. Researches show two important characters of the immune system. First of all, the immune system needs a certain period of time to build up the strongest defense against an infection. Second, the immune system maintains memory of this infection in order to react fast during the second battle with the same disease. Keep these ideas in mind, and we are going to take a look at how can someone become immune to a disease. When you encounter a disease the first time, your immune system steps into the battle. Since it has never faced the enemy before, the immune system spends days to come up with the best plan to remove the infection. During this period of time, the infection continues to cause damage to your body. You'll be sick for days before your immune system eventually wins. The immune system records this battle and put it into archives. When you encounter the same disease the second time, your immune system pulls out the memory immediately. Since the plan is already there, your immune system save its time and respond to the disease right away. Because of the fast reaction of the immune system, the infection is wiped out quickly before it can do much damage to your body. From then on, this disease won't cause you trouble anymore. This brings up the question: can we find a way to introduce immunity to human body without low-risk? The answer is vaccine.
The purpose of vaccine is to introduce protective immunity under a controlled and non-disease causing condition. In history, severe contagious diseases have caused countless death. These diseases are often so strong that the immune system may not have the time it needs to grow its strongest responses. With years of experiences, the help of vaccination has proven to be successful in controlling these diseases. The best example is smallpox. Smallpox is a viral infection that threatened people's lives worldwide in history. In 1976, Edward Jenner found that cowpox virus, which is related to smallpox virus, could also introduce protective immunity to human body against smallpox. Nevertheless, disease caused by cowpox is quite mild on human. By introducing cowpox to human body can prevent the deadly smallpox disease. Before long, this method was applied worldwide. The result was exciting. Smallpox was announced "eliminated" in 1980. Jenner named this method vaccination after vaccinia, the disease caused by cowpox. It is also the first ever case of overcoming disease using vaccine. Nowadays, vaccination has become a common procedure in preventing diseases. Most of those plague causing epidemic diseases once in history has been controlled by vaccination. However, it is not so easy to eradicate a disease. Unfortunately, smallpox is the only successful case that is announced extinction worldwide. Meanwhile, People often worry about the safety of vaccines. Vaccines expose human body to non-disease causing parts or forms of pathogens to trigger immune response. To many of us, this sounds like injecting disease. However, it is not the fact. It takes a lot of research to produce a safe and functional vaccine. In addition, it needs time to show the long-term effects. Before you take a vaccine, it is better to ask your doctor and search online for some information. We should stay alert to unassured vaccines but we should not go against all vaccines or even the idea of getting vaccines. You can believe that vaccines has proven success hundreds of times. They are protecting us every moment right now and will protect us even better in the future. Herd immunity Vaccines protect not only people who get vaccines but also the community they live in. When a high percentage of population get vaccines against a contagious disease in a community, the transmission of the disease breaks. Thus, un-immunized individuals can avoid exposure to the disease and stay healthy. This is known as herd immunity. We'll use an illustration to better demonstrate this topic.
Flu Shot: why do you need a new one each year? Have you ever thought of why would you need a new flu shot every year, while some other vaccines you only need to take once and it can protect you for a lifetime? Influenza disease, which commonly known as flu, is caused by influenza virus. Each time one recovers from flu or takes a flu-shot, his/her immune system develops protective immunity against the infection. It allows the immune system to react quickly during the second exposure of the same infection. The immune system wipes out the virus fast enough so that you do not feel sick. Influenza virus has mutated to a number of strains. These strains compete to infect human body. The protective immunity is built against the first strain it is exposed to. The changing of structures allows the other strains of influenza virus to escape the protective immunity. Your immune system sees each strain of influenza virus as a new type of infection. It then goes to build new protective immunity from sketch. Influenza virus mutates rapidly. The strain that causes epidemic disease each winter is different. The protective immunity one acquired last year by recovering from flu or by flu-shot will lost its efficiency against the new strain of influenza virus. Each year, new flu-shots are developed against the new strains of the influenza virus. These are the reasons why you need a flu-shot each year.
Allergy & transplantation
Allergic reactions On the previous topic, we talked about vaccination, which enhances the performance of immune system. Now we are going to talk about situations when immune response needs to be suppressed. One of the most common example is allergy. The purpose of immune response is to strike invading microorganisms. It is important for the immune system to distinguish the invaders from the human body itself. Besides that, the human body also encounters harmless macromolecules from consuming, inhaling, injection and touching. Immune system should be able to pick out the harmful contacts. However, at times, the immune system mistakes harmless molecules as threats. It then goes to develop adaptive immunity as if there was an infection. This unnecessary reaction results in no good but damage to human tissues. This is called hypersensitivity reactions or simply known as allergic reactions. The molecules that cause allergy are named allergens to be distinguished from pathogens. The population influenced by allergic diseases has been constantly increasing, especially in developed countries where the parasitic infection is rare. The immune system has lost its natural target because of better medication and personal hygiene. The result is that the immune system target harmless environmental elements more often. This is known as the hygiene hypothesis.
Transplantation: blood transfusion Nowadays, transplantation is a choice of treatment that allows the replacement of dis-functional body tissues or organs of a patient. However, since the immune system has the nature of targeting foreign elements, it attacks the transplanted tissues or organs as if they were infections. In this case, suppression of the recipient’s immune response is a key to successful transplantation. When we talk about transplantation, we tend to think about organ transplantation, such as kidney and liver transplantation. But do you know that blood is the tissue that’s been transplanted? Blood transplantation or blood transfusion is given to patient when he/she loses lots of blood due to trauma, surgery, childbirth or disease. Among all the red blood cell antigens, antigen A, B and Rhesus D (RhD) are the most important ones clinically. A, B and RhD each represents one type of antigen, while O means the lack of both antigen A and B. The recipient who lacks any of these three antigens will create corresponding antibodies. This can result in conditions such as fever, chill, shock and more seriously renal failure and death. It is critical to match the ABO and RhD antigens of the donor and the recipient before performing blood transfusion. The method to assure the compatibility of the transfusion is cross-match test.
Immunodeficiency: HIV and SCID Immunodeficiency is the situations in which the immune system collapses. Lacking a functional immune system means defenseless to infections. Pathogens or defective genes can cause immunodeficiency. One of the most known pathogens that causes immune system failure is the human immunodeficiency virus (HIV). HIV infects immune cells. The count of the immune cells declines rapidly. HIV gradually wears down the immune system and progresses to AIDS. AIDS is short for acquired immune deficiency syndrome. It is the final stage of HIV infection, at which the immune system collapses. At this point, the patient lost defense to infections and any minor infection will easily cause death.
Defective genes can also cause immunodeficiency. Patients with severe combined immunodeficiency (SCID), also known as the bubble boy syndrome, cannot develop fully functional immune cells due to defective genes. Their immune system cannot react properly to infections. This makes them vulnerable to infections in normal environments. Leave a comment

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Welcome! The aim of this website is to help people understand basic concepts of immune system. On each part of this website you can read about different topics related to the immune system. These topics are selected to help you have some ideas about how immune system works and why it is important. You can go through the topics in-order or jump to any part you like. What is immune system? Immune system defends human and other animals from diseases. There are countless microorganisms around us. They are invisible to naked eyes. These microorganisms, such as bacteria and virus, cause infectious diseases. The immune system is a series of collaborating physiological mechanisms. It is the key to human survival. How does immune system work? Let us take the immune system as a security agent to our body. There are cells in our body, which have evolved to specialize in defense. As Invasion of microorganisms happens every second, let us think of “health” as a status during which our immune system suppresses infections. Sometimes, you feel sick because the growing of microorganisms overwhelms the immune system. If an infection is not controlled, even a minor cut can eventually be fetal. When the infection is too strong or the immune system is too weak, the immune system fails. Under such circumstances, the help of medication is required. Why should we learn about immune system? People tend to understand health issues with their own experiences or what they believes to be true. Most of these knowledge lacks scientific evidence. The study of immune system builds upon the experiences of medical practices. Numbers of modern medications and treatments are developed with immunological studies. Knowing more of the immune system can help you understand many health related topics better. It can also help you with medical choices. For example, whether or not to get a vaccine. Immune cells & pathogens Before we continue to discuss how the immune system develops, let us talk briefly about immune cells and disease-causing microorganisms. You must have heard of white blood cells. However, do you know there are different kinds of them? Leukocytes, which commonly known as white blood cells, derive from pluripotent hematopoietic stem cells. We will only talk about two of the most important kinds. They are B cell and T cell. B cell derives plasma cell and memory cell. T cell derives helper T cell and cytotoxic T cell. Microorganisms which cause diseases are called pathogens. They are four kinds of them: bacteria, viruses, fungi and parasites. Innate immunity & adaptive immunity There are two types of immunity: innate immunity and adaptive immunity. Innate immunity responds to infection first. It reacts fast to infection. However, the innate immunity treats all the infections the same way. It provides fundamental defense. When the innate immunity is not sufficient to stop the infection, adaptive immunity steps in. The adaptive immunity comes up with solutions to target different infections specifically. It is more powerful than the innate immunity. Because the mechanisms are more complicated, it takes longer to show the effect. However, the adaptive immunity maintains memories of infections. Next time it can react much faster towards pathogen which it is previously exposed to. This is the key to long-term immunity. The Long-term immunity is utilized by scientists to create vaccines. Herd immunity Vaccines protect not only people who get vaccines but also the community they live in. When a high percentage of population get vaccines against a contagious disease in a community, the transmission of the disease breaks. Thus, un-immunized individuals can avoid exposure to the disease and stay healthy. This is known as herd immunity. We'll use an illustration to better demonstrate this topic. Flu Shot: why do you need a new one each year? Have you ever thought of why would you need a new flu shot every year, while some other vaccines you only need to take once and it can protect you for a lifetime? Influenza disease, which commonly known as flu, is caused by influenza virus. Each time one recovers from flu or takes a flu-shot, his/her immune system develops protective immunity against the infection. It allows the immune system to react quickly during the second exposure of the same infection. The immune system wipes out the virus fast enough so that you do not feel sick. Influenza virus has mutated to a number of strains. These strains compete to infect human body. The protective immunity is built against the first strain it is exposed to. The changing of structures allows the other strains of influenza virus to escape the protective immunity. Your immune system sees each strain of influenza virus as a new type of infection. It then goes to build new protective immunity from sketch. Influenza virus mutates rapidly. The strain that causes epidemic disease each winter is different. The protective immunity one acquired last year by recovering from flu or by flu-shot will lost its efficiency against the new strain of influenza virus. Each year, new flu-shots are developed against the new strains of the influenza virus. These are the reasons why you need a flu-shot each year. Allergy & transplantation Allergic reactions On the previous topic, we talked about vaccination, which enhances the performance of immune system. Now we are going to talk about situations when immune response needs to be suppressed. One of the most common example is allergy. The purpose of immune response is to strike invading microorganisms. It is important for the immune system to distinguish the invaders from the human body itself. Besides that, the human body also encounters harmless macromolecules from consuming, inhaling, injection and touching. Immune system should be able to pick out the harmful contacts. However, at times, the immune system mistakes harmless molecules as threats. It then goes to develop adaptive immunity as if there was an infection. This unnecessary reaction results in no good but damage to human tissues. This is called hypersensitivity reactions or simply known as allergic reactions. The molecules that cause allergy are named allergens to be distinguished from pathogens. The population influenced by allergic diseases has been constantly increasing, especially in developed countries where the parasitic infection is rare. The immune system has lost its natural target because of better medication and personal hygiene. The result is that the immune system target harmless environmental elements more often. This is known as the hygiene hypothesis. Transplantation: blood transfusion Nowadays, transplantation is a choice of treatment that allows the replacement of dis-functional body tissues or organs of a patient. However, since the immune system has the nature of targeting foreign elements, it attacks the transplanted tissues or organs as if they were infections. In this case, suppression of the recipient’s immune response is a key to successful transplantation. When we talk about transplantation, we tend to think about organ transplantation, such as kidney and liver transplantation. But do you know that blood is the tissue that’s been transplanted? Blood transplantation or blood transfusion is given to patient when he/she loses lots of blood due to trauma, surgery, childbirth or disease. Among all the red blood cell antigens, antigen A, B and Rhesus D (RhD) are the most important ones clinically. A, B and RhD each represents one type of antigen, while O means the lack of both antigen A and B. The recipient who lacks any of these three antigens will create corresponding antibodies. This can result in conditions such as fever, chill, shock and more seriously renal failure and death. It is critical to match the ABO and RhD antigens of the donor and the recipient before performing blood transfusion. The method to assure the compatibility of the transfusion is cross-match test. Immunodeficiency: HIV and SCID Immunodeficiency is the situations in which the immune system collapses. Lacking a functional immune system means defenseless to infections. Pathogens or defective genes can cause immunodeficiency. One of the most known pathogens that causes immune system failure is the human immunodeficiency virus (HIV). HIV infects immune cells. The count of the immune cells declines rapidly. HIV gradually wears down the immune system and progresses to AIDS. AIDS is short for acquired immune deficiency syndrome. It is the final stage of HIV infection, at which the immune system collapses. At this point, the patient lost defense to infections and any minor infection will easily cause death. Leave a comment Defective genes can also cause immunodeficiency. Patients with severe combined immunodeficiency (SCID), also known as the bubble boy syndrome, cannot develop fully functional immune cells due to defective genes. Their immune system cannot react properly to infections. This makes them vulnerable to infections in normal environments. What is vaccine? How does it protect us from disease? The purpose of vaccine is to prevent disease. But how dose it work? The most basic idea is that the immunity is adaptive. In the early days, people found that some of those who survived from epidemic disease won't catch the same disease again. They are "immune" to the disease. This observation brings up study of human immune system. Researches show two important characters of the immune system. First of all, the immune system needs a certain period of time to build up the strongest defense against an infection. Second, the immune system maintains memory of this infection in order to react fast during the second battle with the same disease. Keep these ideas in mind, and we are going to take a look at how can someone become immune to a disease. When you encounter a disease the first time, your immune system steps into the battle. Since it has never faced the enemy before, the immune system spends days to come up with the best plan to remove the infection. During this period of time, the infection continues to cause damage to your body. You'll be sick for days before your immune system eventually wins. The immune system records this battle and put it into archives. When you encounter the same disease the second time, your immune system pulls out the memory immediately. Since the plan is already there, your immune system save its time and respond to the disease right away. Because of the fast reaction of the immune system, the infection is wiped out quickly before it can do much damage to your body. From then on, this disease won't cause you trouble anymore. This brings up the question: can we find a way to introduce immunity to human body without low-risk? The answer is vaccine. The purpose of vaccine is to introduce protective immunity under a controlled and non-disease causing condition. In history, severe contagious diseases have caused countless death. These diseases are often so strong that the immune system may not have the time it needs to grow its strongest responses. With years of experiences, the help of vaccination has proven to be successful in controlling these diseases. The best example is smallpox. Smallpox is a viral infection that threatened people's lives worldwide in history. In 1976, Edward Jenner found that cowpox virus, which is related to smallpox virus, could also introduce protective immunity to human body against smallpox. Nevertheless, disease caused by cowpox is quite mild on human. By introducing cowpox to human body can prevent the deadly smallpox disease. Before long, this method was applied worldwide. The result was exciting. Smallpox was announced "eliminated" in 1980. Jenner named this method vaccination after vaccinia, the disease caused by cowpox. It is also the first ever case of overcoming disease using vaccine. Nowadays, vaccination has become a common procedure in preventing diseases. Most of those plague causing epidemic diseases once in history has been controlled by vaccination. However, it is not so easy to eradicate a disease. Unfortunately, smallpox is the only successful case that is announced extinction worldwide. Meanwhile, People often worry about the safety of vaccines. Vaccines expose human body to non-disease causing parts or forms of pathogens to trigger immune response. To many of us, this sounds like injecting disease. However, it is not the fact. It takes a lot of research to produce a safe and functional vaccine. In addition, it needs time to show the long-term effects. Before you take a vaccine, it is better to ask your doctor and search online for some information. We should stay alert to unassured vaccines but we should not go against all vaccines or even the idea of getting vaccines. You can believe that vaccines has proven success hundreds of times. They are protecting us every moment right now and will protect us even better in the future. Immunity & vaccination To make things short, there are three features of the immune system you need to know. They can help you understand many discussions related to modern medicine: 1. Immune system is crucial to survival 2. Immune system grows stronger over time. 3. Immunity provides future protection.