Immune System (for Parents)
and uro-genital tracts protect us by competing with pathogens for attachment and The innate immune system has certain "sentinel cells (monocytes, .. CDC Recommendation for Post-Exposure Prophylaxis to Hepatitis A As a result, newborn infants receive some passive immunity from antigens to which their mother. This evidence and the AAP recommendation support the incorporation of . Breastfeeding is often mentioned as a facilitator of mother-infant bonding (77), and . Protection of the neonate by the innate immune system of developing gut and of. Unlike the innate immune system, which attacks only based on the identification Plasma B cells produce the same antibody as the parent B cell, but they aren't .
These MHC molecules are membrane-bound surface receptors on antigen-presenting cells, like dendritic cells and macrophages. Macrophage binding to T cell T cell receptors have to undergo a process called rearrangement, causing the nearly limitless recombination of a gene that expresses T cell receptors.
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The process of rearrangement allows for a lot of binding diversity. Mature T cells should recognize only foreign antigens combined with self-MHC molecules in order to mount an appropriate immune response.
T cell positive selection and negative selection In order to make sure T cells will perform properly once they have matured and have been released from the thymus, they undergo two selection processes: In order to pass the positive selection process, cells must be capable of binding only self-MHC molecules.
If these cells bind nonself molecules instead of self-MHC molecules, they fail the positive selection process and are eliminated by apoptosis. Negative selection tests for self tolerance. Negative selection tests the binding capabilities of CD4 and CD8 specifically. The ideal example of self tolerance is when a T cell will only bind to self-MHC molecules presenting a foreign antigen.
These two selection processes are put into place to protect your own cells and tissues against your own immune response. They were renowned for their unblemished skin. In he infected a young boy with cowpox, allowed him to fully recover, and then intentionally injected the boy with pus from a smallpox lesion. The boy did not become ill. Jenner published a book and people began intentionally infecting themselves with cowpox. It was called "vaccination," after "vacca," the Latin word for cow, and the substance used to vaccinate was called a "vaccine.
If the same pathogen invades the organism again, the memory cells will again bind to the pathogen and begin to replicate, but memory cells can replicate more quickly. As a result, a secondary exposure to a given antigen triggers an immune response that is much more rapid and more vigorous than that seen with the first exposure.
Types of Vaccine "Inactivated" or "killed" vaccines that use formalin to kill the agent, e. These cannot induce disease, and are safe for immunocompromised people. Hemophilus influenza B vaccine. However, live, attenuated vaccines are riskier, since they can mutate back to the virulent form. Therefore, not recommended for immunocompromised patients.
Vaccines made from toxins. The toxin is converted into a harmless "toxoid" by treating it with aluminum. These often induce low level immune responses and are sometimes given with an "adjuvant" - an agent that increases the immune response. For example, diphtheria and tetanus vaccines are often combined with pertussis vaccine and given together as a DPT immunization.
The pertussis acts as an adjuvant in this vaccine. When more than one vaccine is administered together it is called a "conjugated vaccine. Vaccines from similar organisms that do not cause serious disease e. Jenner used cowpox vs. BCG vaccine used to protect against Mycobacterium tuberculosis is an attenuated strain of Mycobacterium bovis and requires boosters every 3 - 4 years. Genes that encode for subunits of the infectious agent are isolated and inserted into bacteria or yeast cells that produce large quantities of subunit molecules by transcribing and translating the inserted foreign DNA.
These are isolated, purified, and used as a vaccine. These are safe for immunocompromised patients because they cannot cause the disease.
Passive Immunity Active immunity occurs when an individual is infected with a pathogen or if they are vaccinated. Exposure to the pathogen's antigens by either of these will result in a primary immune response and immunologic memory.
However, it is also possible in some circumstances to protect a susceptible person by giving them the antibodies produced by another person. For example, if we were to take serum from people who had previously been infected with hepatitis A virus HAVit would contain significant concentrations of IgG against HAV. It is possible to pool serum from previously infected individuals and then inject this immunoglobulin G into individuals who may have been recently been exposed to HAV in order to thwart the infection and prevent them from becoming a clinically active case.
In essence, passive immunization: However, this passive form of protection bypasses the steps in primary exposure, and it does not produce immunologic memory. Moreover, the protection afforded by this passive form of immunity only lasts as long as the exogenous antibodies, about months. After the exogenous antibodies disappear, the individual is just as susceptible as a person who had never been exposed. The guidelines vary by age and health status: For healthy persons aged 12 months—40 years, single-antigen Hepatitis A vaccine at the age-appropriate dose is preferred to IG because of the vaccine's advantages, including long-term protection and ease of administration, as well as the equivalent efficacy of vaccine to IG.
For persons aged 40 years and older, IG is preferred because of the absence of information regarding vaccine performance in this age group and because of the more severe manifestations of Hepatitis A in older adults. The magnitude of the risk of HAV transmission from the exposure should be considered in decisions to use vaccine or IG in this age group. Vaccine can be used if IG cannot be obtained. IG should be used for children aged less than12 months, immunocompromised persons, persons with chronic liver disease, and persons who are allergic to the vaccine or a vaccine component" IgG is able to cross the placenta from mother to fetus.
As a result, newborn infants receive some passive immunity from antigens to which their mother has been exposed. However, this passive protection disappears over a period of months, so it is important for the infant to develop active immunity through vaccinations or by being infected and developing clinical disease. The decline in passive immunity in an infant is what dictates the recommended schedule of immunizations for infants.
Specificity of the Adaptive Immune System Each lymphocyte has only one type of epitope receptor, but pathogens have many potential antigenic molecules, each of which may have several epitopes.
In addition, the epitopes for some pathogens, such as those on influenza's hemagglutinen protein, change from year to year as a result of mutations. Consequently, the number of possible foreign epitopes is enormous, but the human genome only has about 30, genes. In view of this, how does the immune system manufacture all of the lymphocyte receptors needed to recognize so many different epitopes? This is accomplished through gene spicing.
- Adaptive immunity
In most cases, a single gene encodes for a single protein. However, lymphocyte receptor proteins are produced by a different process. The stem cells that produce lymphocytes have a pool of genes which encode for peptides in lymphocyte receptors.
During development and maturation of lymphocytes, most of these genes are eliminated, and only randomly selected genes are retained and spliced together. This spliced sequence encodes for receptors in the mature lymphocytes.
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The pool of receptor genes in stem cells is like a deck of cards. Each lymphocyte that is produced is dealt of these at random, and the genes can be shuffled into any order before they are spliced together.
As a result, it is possible to synthesize a hundred million different receptors from the original pool of genes. When it matures, each lymphocyte can manufacture just one type of epitope receptor. This short video summarizes the process by which specific antibodies are made. Self-Tolerance Through Lymphocyte Selection How does the immune system avoid attacking our own cells which also have potentially antigenic shapes?
As a result of the random selection and splicing of genes to create unique receptors, some of the lymphocytes created will have receptors that would bind our own proteins. However, during the maturation process in the thymus gland, those lymphocytes are induced to undergo apoptosis programmed cell deathand they are permanently eliminated.
Summary of Adaptive Immunity The image below provides a brief summary of innate and adaptive immunity. The left-hand portion of the image shows a macrophage binding to a bacterium via its toll-like receptors. This initiates engulfment and breakdown of the bacterium and the "presentation" of bacterial epitopes on the MHC class II molecules inserted into the surface of the macrophage. In essence, this provides an important interface between the innate and adaptive immune systems, because the presentation of antigens by the macrophage provides an opportunity to stimulate helper T cells and B cells, which are part of the adaptive immune system.
Helper T cells will further activate B cells and promote their replication and differentiation into plasma cells that will produce antibodies that will specifically tag that epitope and aid in identification and destruction of the bacteria by macrophages and neutrophils. While not shown here, engulfment of a pathogen by a macrophage and damage to local cells would also trigger an inflammatory response, which would entail release of a variety of cytokines and chemoattractants, dilation of local blood vessels, and translocation of neutrophils, fluid, and complement proteins from capillaries into the affected tissue.
The image on the far right above shows a human cell that has become infected with virus. As part of its normal "self-checking," all proteins synthesized inside the cell including viral proteins are sampled and broken down, and selected fragments are "presented" on the MHC class I molecules present in all nucleated cells. Helper T cells with matching receptors will become activated and will release a variety of cytokines to recruit and activate B cells and cytotoxic T cells with matching receptors.
These also will replicate over and over, forming large clones of identical cells. Cytotoxic T cells will then bind to cells displaying that particular epitope, and they will release cytotoxic substances that will kill the infected cells, thereby shutting off further production of virus.
The activated B cells will differentiate into plasma cells that produce antibody specific for the viral epitopes and will bind to extracellular viruses, effectively neutralizing them so that they are unable to bind to and infect other cells. The antibody tags will also aid in the phagocytosis of viruses tagged with antibody. Note also that natural killer cell NK cells can also attack cells with missing or abnormal MHC molecules as a result of viral infection or cancer.
NK cells are a special class of lymphocytes that are considered part of the innate immune system, because their action is non-specific, i.
Lymphocytes in the Adaptive Immune System Deficient Immunity There are a number of conditions that cause deficient immune responses. Inherited Immunodeficiency Inherited immunodeficiency disorders can result in inability to produce antibodies, such as: Hypogammaglobulinemia Agammaglobulinemia, which results in severe infections early in life, and is often deadly Acquired Immunodeficiency Deficient immune response can also be the result of any number of acquired conditions, including: The number of lymphocytes does not change, but their ability to defend against infection seems to diminish with age.
Cancer Iatrogenic causes, e. Allergy Allergies are undesirable inflammatory responses to environment exposures that are harmless to most people. A wide variety of substances can trigger an allergic reaction referred to as allergensincluding plant pollen, foods e. Some individuals are "atopic," meaning that they have an inherited predisposition to developing allergies. Exposure to an allergen in an allergic individual triggers the secretion of IgE antibodies, which trigger the release of histamine and other mediators from mast cells and basophils when the antibody binds to the allergen.
The magnitude of the resulting inflammatory response can vary widely, ranging from mild to moderately severe local symptoms e. Autoimmune Disorders Autoimmune disorders are those in which an individual's immune system attacks its own tissues and organs. The underlying causes of autoimmune disease are not well understood, but one theory is that infections or other injuries to tissues cause alterations that confuse the ability of our immune system to distinguish between "self" and "non-self".
In this way, the immune system works in a coordinated manner to monitor the body for germs or substances that might cause problems.
The two basic types of leukocytes are: If doctors are worried about a bacterial infection, they might order a blood test to see if a patient has an increased number of neutrophils triggered by the infection. Other types of phagocytes have their own jobs to make sure that the body responds appropriately to a specific type of invader.
The two kinds of lymphocytes are B lymphocytes and T lymphocytes. Lymphocytes start out in the bone marrow and either stay there and mature into B cells, or they leave for the thymus gland, where they mature into T cells. B lymphocytes and T lymphocytes have separate functions: B lymphocytes are like the body's military intelligence system, seeking out their targets and sending defenses to lock onto them.
T cells are like the soldiers, destroying the invaders that the intelligence system has identified. Here's how it works: These cells trigger the B lymphocytes to produce antibodies, which are specialized proteins that lock onto specific antigens. So if someone gets sick with a certain disease, like chickenpox, that person usually won't get sick from it again. This is also how immunizations prevent certain diseases.
An immunization introduces the body to an antigen in a way that doesn't make someone sick, but does allow the body to produce antibodies that will then protect the person from future attack by the germ or substance that produces that particular disease.
Although antibodies can recognize an antigen and lock onto it, they are not capable of destroying it without help. That's the job of the T cells, which are part of the system that destroys antigens that have been tagged by antibodies or cells that have been infected or somehow changed.
Some T cells are actually called "killer cells. Antibodies also can neutralize toxins poisonous or damaging substances produced by different organisms. Lastly, antibodies can activate a group of proteins called complement that are also part of the immune system. Complement assists in killing bacteria, viruses, or infected cells. All of these specialized cells and parts of the immune system offer the body protection against disease.
This protection is called immunity. Immunity Humans have three types of immunity — innate, adaptive, and passive: Innate Immunity Everyone is born with innate or natural immunity, a type of general protection. Many of the germs that affect other species don't harm us.
For example, the viruses that cause leukemia in cats or distemper in dogs don't affect humans. Innate immunity also includes the external barriers of the body, like the skin and mucous membranes like those that line the nose, throat, and gastrointestinal tractwhich are the first line of defense in preventing diseases from entering the body.