Immunity – Humans are Exposed with Microbes
Humans are exposed with microbes that contain a vast array of allergenic substances that threaten normal homeostasis. Therefore, immune system is important to defend body from pathogens. It is eliminating pathological microbes and toxic or allergenic proteins, but at the same time it must avoid responses that produce excessive damage of self-tissues or that might eliminate beneficial, commensal microbes. A general feature of the immune system is that its mechanisms that rely on detecting structural features of the pathogen or toxin that mark it as distinct from host cells. Such host-toxin discrimination is essential to permit the host to eliminate the threat and keeping its own tissues from damage. The immune system, which is made up of special cells, such as tissues, proteins and organs, defends people against germs and microorganisms every day. In most cases, the immune system is developing immunity which helps keeping people healthy by being able to resist a particular disease. However, sometimes problems with the immune system can lead to illness and infection.
All of these special cells and parts of the immune system is needed for the body protection against disease. This protection is called immunity. There are four types of immunity. First is the Innate (Natural) immunity. It is the natural resistance components such as intact skin, salivary enzymes, and neutrophils, natural killer cells, which acts as the first to respond against infection.It is present in an individual since birth prior to exposure to a pathogen or antigen. Second type is Adaptive (acquired) Immunity which develops antibodies after an attack of an infectious disease or by a pregnant mother passing through the placenta to a fetus or by vaccination. Third type is called Active immunity which refers to the method of exposing the body to an antigen for generating an adaptive immune response. The response takes days/ weeks to develop but may be long- lasting. For example recovery from Hepatitis-A virus gives a natural active immune response that usually leading lifelong protection. In a similar manner, administration of two doses of Hepatitis-A vaccine generates an acquired active immune response which leading to long lasting defense. The forth one is Passive immunity which refers to the process of imparting IgG antibodies to keep safe against infection. It gives immediate, but short- lived protection such as several weeks to 3 or 4 months at most. It is occurs during pregnancy. The transfer of maternal tetanus antibody (mainly IgG) across the placenta provides passive immune to newborn baby for several weeks/ months until such antibody is degraded and lost.
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How it works
The immune system mechanism employs many potent effector that have the ability to destroy a broad range of microbial cells and to clear a broad range of toxic and allergenic substances. It is therefore, that this immune response is able to avoid release these destructive mechanisms against the host’s own tissues. The ability of the immune response to avoid damaging self-tissues is referred to as self-tolerance. Because failure of self-tolerance underlies the broad class of autoimmune diseases, this process has been extensively studied. It is now clear that mechanisms to avoid reaction against self-antigens are expressed in many parts of both the innate and the adaptive immune response. The important aspect of the T cell arm of the immune system is to be able to recognize host cells that are being infected by viruses, intracellular bacteria or other parasites, T cells have gradually developeda mechanism that recognizes foreign antigens together with self-antigens as a molecular complex.
This requirement that T cells recognize both self-structures and foreign antigens make the need for these cells to maintain self-tolerance particularly important.The first set of responses constitutes the innate immune response. The innate response includes soluble proteins and bioactive small molecules such as the complement proteins, defensins, and ficolins1–3 or that are released from cells as they are activated. It includes cytokines that acts as a regulator of the function of other cells, chemokines that attract inflammatory leukocytes, lipid mediators of inflammation, reactive free radical species, and bioactive amines and enzymes that also contribute to tissue inflammation. Because the recognition molecules used by the innate system are expressed broadly on a large number of cells, this system is poised to act rapidly after an invading pathogen or toxin is encountered and thus constitutes the initial host response. In cellular elements of the immune Response, an intact immune response includes contributions from many subsets of leukocytes. The different leukocyte subsets can be discriminated morphologically by a combination of conventional histological stains, and by analysis of the spectrum of glycoprotein differentiation antigens that are displayed on their cell membranes.
The second set of responses is the adaptive immune response. Because the adaptive system is composed of small numbers of cells with specificity for individual pathogen, toxin or allergen, the responding cells must proliferate after detecting the antigen in order to attain an effective response against the microbe or the toxin. Thus, the adaptive response generally expresses itself temporally after the innate response in host defense. A key feature of the adaptive response is that it produces long-lived cells that persist in an apparently dormant state, but that can re-express effector functions rapidly after another encounter with their specific antigen. This provides the adaptive response with the ability to manifest immune memory, permitting it to contribute prominently to a more effective host response against specific pathogens or toxins when they are encountered a second time, even decades after the initial sensitizing encounter.
When antigens (foreign substances that invade the body) are detected, several types of cells work together to recognize them and respond. These cells trigger the B lymphocytes to produce antibodies, which are specialized proteins that lock onto specific antigens. Once produced, these antibodies stay in a person’s body, so that if his or her immune system encounters that antigen again, the antibodies are already there to do their job. 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.
Cell death is a loss of plasma membrane integrity and it can be classified according to its morphological appearance, enzymological criteria, functional aspects or immunological characteristics.Necrosisis best defined by light or electron microscopic detection of cell and organelle swelling or rupture of surface membranes with spillage of intracellular contents (Richard S, 2009). If the infection is severe, the infected cells will eventually die and resulting in increased inflammation which can cause delay of healing process.Accumulating evidence indicates that necrosis is more ordered than was originally thought. When cells die from necrosis, damage-associated molecular-pattern (DAMP) molecules, such as high-mobility group protein, enter the circulation and activate innate immune cells. Apoptosis (programmed death) infected cells die to prevent further damage to the body and helps in healing process.Most chemotherapeutic agents induce apoptosis in tumor cells. The tyrosine kinase inhibitor imatinib (Gleevec) kills chronic myeloid leukemia cells by up-regulating the proapoptotic BCL2 family members. In multicellular organisms, cells that are no longer needed or are a threat to the organism are destroyed by a tightly regulated cell suicide process known as programmed cell death, or apoptosis.
Apoptosis is mediated by an enzyme called caspases, which trigger cell death by cleaving specific proteins in the cytoplasm and nucleus. Caspases exist in all cells as inactive precursors, or procaspases, which are usually activated by cleavage by other caspases, and producing a proteolyticcaspase cascade. The activation process is initiated by either extracellular or intracellular death signals, which then cause intracellular adaptor molecules to aggregate and activate procaspases. Caspase activation is regulated by members of the Bcl-2 and IAP protein families. Cells that die as a result of acute injury will swell and burst. They spill their contents all over their neighbors and this is a process called cell necrosis which causing a potentially damaging inflammatory response. Meanwhile, a cell that undergoes apoptosis dies neatly, without damaging its neighbors. The cell condensesand shrinks. The cytoskeleton will collapse, the nuclear envelope disassembles, and the nuclear of DNA breaks up into fragments. Most importantly, the cell surface is altered, displaying properties that cause the dying cell to be rapidly phagocytosed, either by a neighboring cell or by a macrophage. Excess macrophages die to ensure all remnants of the pathogen and antigen are got rid for better healing process.
The immune system uses many different mechanisms in order to combat infection caused by microbes. These mechanisms work together, and evolved a fully integrated immune response that draws elements from many effector systems in order to adapt a response to the specific invading pathogen. Abnormal regulation of the various effector mechanisms can lead to chronic or acute tissue damage. Understanding the relationships between the different immune effector pathways will permit improved immunomodulatory therapeutics, development of improved vaccines, and avoidance of unintended tissue injury and helps to further fasten the healing process.”