Exam 4: Chapter 17 Immunology
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82 terms
Terms | Definitions |
|---|---|
 Immunity | The ability of an organism to recognize and defend itself against infectious agents |
| Susceptibility | The vulnerability of the host to harm by infectious agents |
| Innate defenses | Immunity against any invading infectious agent - also called genetic immunity because of genetically determined characteristics |
| Adaptive (acquired) defenses | Immunity against specific antigens on infectious agents - obtained in some manner other than by direct heredity: can be acquired naturally following infection or artificially EX. vaccination |
| Active immunity | is created when one's immune system activates T cells, or produces antibodies or other defenses against an infectious agent. Period of immunity varies - weeks, months or years |
| Naturally acquired active immunity | is produced when one is exposed to infectious agent |
| Artificially acquired active immunity | is vaccinated with live, weakened, or dead organisms or their toxins |
| Passive Immunity | is created when ready-made antibodies are introduced into the body; host's body does not make antibodies |
| Naturally acquired passive immunity | produced when antibodies made by the mother's immune system are transferred to a fetus across the placenta or to an offspring in colostrum and breast milk |
| Artificially acquired passive immunity | is produced by other hosts are introduced into a new host. Does not stimulate the host's immune system to produce antibodies. Period of immunity persists for a few weeks or months and then the antibodies are destroyed by the host, eg antibodies against snake venom |
| Antigen | a substance that the body recognizes as foreign and towards which it mounts an immune response. Also known as immunogens, antigens can be large protein molecules or polysaccharides, few are glycoproteins or nucleoproteins |
| Epitopes | or antigenic determinants, areas on the molecule to which antibodies bind. Large complex protein molecules can have several (more than one epitope) |
| Hapten | small molecule that act as an antigen if it binds to a larger protein molecule. Haptens act as epitopes on the surface of the protein. Hapten or the protein component cannot act as an antigen but the complex can. Eg penicillin |
| Antibody | a protein produced in response to an antigen that is capable of binding specifically to the antigen. each kind of antibody binds to a specific antigen antigenic determinant such binding may or may not contribute to the inactivation of the antigen |
| Titer | The quantity of antibody required to bind and to neutralize a particular quantity of antigen |
| Lymohocytes | Specific immune responses are carried out by these and they develop from stem cells. Undifferentiated stem cells from the yolk sac migrates through the umbilical cord into the body and at various sites they differentiate into different types of lymphocytes |
| B lymphocytes or B cells | Differentiation of stem cells takes place in bone marrow. Functional cells found in all lymphoid tissues - lymph nodes, spleen, tonsils, adenoids and gut associates tissues (GALT)which are lymphoid tissues in the digestive tract, including the appendix and Peyer's patches of the small intestine |
| T lymphocytes or T cells | Differentiation takes place in the thymus, but the frequency of differentiation is lower in adulthood. T cells are found in all tissues that contain B cells and account for three fourths of the lymphocytes circulating in the blood |
| The four kinds of cells that T cells produce | 1. cytotoxic (killer) T cells 2. delayed hypersensitivity T cells 3. helper T cells 4. regulatory T cells |
| Natural killer cells or NK cells | Those lymphocytes that cannot be identified as either B cells or T cells are found in tissues and circulating in blood eg. NK cells They nonspecifically kill cancer cells and cells infected with viruses without having to use specific immune responses They "naturally" kill cells by releasing various cytotoxic molecules some of which make holes in the target cell's membrane, leading to cell lysis. Others enter the cell and fragments its nuclear DNA causing apoptosis (programmed cell death) |
| The two major types of immune responses that lymphocytes give rise to | Humoral immunity and cell mediated immunity |
| Humoral Immunity | carried out by antibodies circulating in the blood when stimulated by an antigen, B lymphocytes initiate a process that leads to the release of antibodies most effective in defending the body against foreign substances outside of cells, such as bacterial toxins, bacteria and viruses before these agents enter cells |
| Cell MEdiated Immuntiy | Carried out by T cells Occurs at cellular level, especially in situations where antigens are embedded in cell membranes or are inside and thus inaccessible to antibodies Most effective in clearing the body of virus infected cells, other eukaryotic parasites, cancer, and foreign tissues, such as transplanted organs |
| Common attributes of humoral and cell-mediated responses that enable them to confer immunity | Self vs. non-self regulation Specificity Diversity Memory |
| Recognition of self vs. non-self | Immune must distinguish between host tissues and substances that are "foreign to the host" Normal host substances are referred to as self and foreign substances as nonself According to clonal selection hypothesis, embryos contain many different lymphocytes, each genetically programmed to recognize a particular antigen and make antibodies to destroy it If a lymphocyte encounters and recognizes that antigen after development is complete, it divides repeatedly to produce a clone, a group of identical progeny cells that make the same antibody If, during development in bone marrow (B cells) or thymus (T cells), it encounters its programmed antigen as part of a normal host substance (self), the lymphocyte is somehow destroyed or inactivated. This mechanism removes lymphocytes that can destroy host tissues and thereby creates tolerance for self |
| Specificity | Mature immune system (2 to 3 years of age) can recognize a vast number of foreign substances as nonself It reacts in a different way to each foreign substance. |
| Cross-reaction | reactions of a particular antibody with very similar antigens |
| Diversity | In a lifetime, human body encounters countless numbers of different foreign antigens This property refers to the ability of the immune system to produce many different kinds of antibodies and T cell receptors, each of which reacts with a different epitope (antigenic determinant) When a bacterium or other foreign agent has more than one kind of antigenic determinant, the immune system may make a different antibody against each Exposure to antigen is not necessary for diversity of antibody and T cell receptors. Lab animals in a germ free environment still produce B cells and T cells with receptors specific for various antigens to which the animals have not been exposed |
| Memory | In addition to its ability to respond to an assortment of antigens, the immune system can recognize substances it has previously encountered This allows the immune system to respond rapidly and defend the body against an antigen to which it has previously reacted In addition to producing antibodies during its first reaction to the antigen, the immune system also makes memory cells. |
| Memory cells | These cells stand ready for years or decades to quickly initiate antibody production following subsequent exposure to an antigen |
| Anamnestic (secondary) response | The prompt response due to "recall" by memory cells |
| Antibody anatomy | heavy/light chains Variable/constant regions Antigen binding site disulfide bridges |
| Immunoglobulin Classes | IgG, IgM, IgA, IgE, IgD |
| IgG | the main class of antibodies found in blood accounts for 20% of plasma proteins, only immunoglobulin that can cross placenta produced in large amounts during secondary response, can activate complement complement consists of proteins that lyse microroganisms |
| IgA | occurs in small amounts in blood but in larger amounts in body secretions such as tears, milk, saliva and mucus abundant in colostrums where it helps protect infants from intestinal pathogens |
| IgM | found as a monomer on the surface of B cells and is secreted as a pentamer by plasma cells first antibody formed in life being synthesized by fetus secreted during the early stages of primary response high levels indicate recent infection or exposure to antigen |
| IgE | has special affinity for receptors on the plasma membrane of basophiles in blood or mast cells in tissues upon binding of IgE the associated basophiles or mast cells secrete substances such as histamine, which produces allergic symptoms Levels of IgE are elevated in patients with allergies and in those harboring worm parasites IgE is found in body fluids and skin, rarely in blood |
| IgD | found mainly on B cell membranes and is rarely secreted it can bind to specific antigens but the exact function is not known may help initiate immune responses and some allergic reactions IgD levels rise in some autoimmune condition |
| Primary Response | in humoral immunity, this to an antigen occurs when antigen is first recognized by host B cells after recognizing the antigen, B cells divide to form plasma cells, which then synthesize antibodies antibody concentration increase over a period of 1 to 10 weeks the first antibodies are IgM, which can bind to foreign substances directly cytokines trigger proliferating B cells to switch making IgG and concentration of IgM wanes as more IgG is produced finally concentration of both IgM and IgG become undetectable B cells that have proliferated and become memory cells persist in lymphoid tissues where they can survive without dividing for many months or many years |
| Secondary Response | when an antigen recognized by memory cells enters the blood the presence of large numbers of memory cells makes secondary response faster than primary response some memory cells divide and form plasma cells while others proliferate and form more memory cells Plasma cells produce large amounts of antibodies, IgM followed by IgG However IgM is produced in smaller quantities and over a shorter period compared to IgG |
| T-independent | T helper cells are not required the response produces only IgM antibody and no B memory cells |
| T-dependent | for most antigens B cell activation requires contact with TH cells the activated TH cells then produce/secrete lymphokines that further activate the B cell causing it to differentiate and proliferate, producing B memory cells and plasma cells so that IgG can be produced |
| Inactive antigen-antibody complexes | Antibodies produced by humoral immune responses eliminate foreign agents by forming these. |
| The nature of inactivation varies according to... | the nature of antigen and the kind of antibody with which it reacts |
| Inactivation can be accomplished by such processes as | Agglutination Opsonization Complement mediated effects Neutralization |
| Agglutination | Bacterial cells are large, and the complexes formed as a result of antigen-antibody interaction also are large. Such reactions result in agglutination or sticking together of microbes |
| Opsonization | • Some antibodies act as opsonins. They neutralize toxins and coat microbes so that they can be phagocytized |
| Activation of complement | Complement is an important component in inactivating infectious agents. Both IgG and IgM are powerful activators of the complement system. IgA is less powerful. Sometimes, antibodies, especially IgM directly lyse cell membranes of infectious agents without the aid of complement |
| Neutralization | The phenomenon in which bacterial toxins, being small molecules secreted from the cell, usually are inactivated simply by the formation of antigen-antibody complexes IgG is the main neutralizer of bacterial toxins. This phenomenon does not stop the organism from producing more toxins. Antibiotics are needed to prevent persisting organisms from continuing to produce toxins Viruses, too, can be inactivated by this; IgM, IgG and IgA are all effective neutralizers of viruses. Those viruses that have an envelope may then be lysed by complement |
| In contrast to humoral immunity which involves B cells and immunoglobins... | cell-mediated immunity involves the direct actions of T cells |
| In cell-mediated immunity, | T cells interact directly with other cells that display foreign antigens |
| What the cell-mediated immune response involves | the differentiation and actions of different types of T cells and the production of cytokines |
| Cytokines | Chemical mediators (lymphokines and interleukins) |
| How T cells produced in the Thymus differ from B cells | They do not make antibodies |
| Can T cells be activated directly by antigens? | No |
| What T cell-mediated response requires | THe presentation of the antigen on the surface of cells along with major histocompatibilty complex proteins |
| What the cell-mediated immune response typically begins with | The processing of an antigen - usually associated with a pathogenic organism - by B cells, dendritic cells, or macropahges |
| What happens when macrophages and dendritic cells phagocytize pathogens | they ingest and degrade the pathogen |
| What hapens when the pieces of the pathogen (peptides) are transported ti the cell surface? | Some of the pathogen's antigen gest incorporated into their own cell membrane |
| How the peptides bind to the cell surface | by MHC II proteins |
| When a macrophage presents the antigen to T cells that have the proper antigen receptor... | the antigen receptor bind |
| How T helper cells are activated | By antigen presented by MHC II, antigen presenting cells |
| How cytotoxic cells are activated | By antigen presented by MHC I, typcically cells infected with virus, intracellular bacterial pathogens, transformed cancer cells, or foreign tissues such as an organ transplant |
| What can T helper cells do once they are activated? | They can stimulate other T and B cells as well as phagocytes |
| Some bacteria, such as those that cause tuberculosis, Hansen's disease (leprosy), listeriasis | can continue to grow even after they have been engulfed by macrophages |
| What do Td cells release to combat infections? | The lymphokine macrophage factor |
| The lymphokine macrophange activating factor | This factor causes macrophages to increase production of toxic hydrogen peroxide (H2O2) along with enzymes that attack the phagocytized organisms and accelerate inflammatory response |
| Superantigens | Such as staphylococcal toxins (that cause food poisoning, toxic shock syndrome and scaled skin syndrome) or streptococcal toxins (responsible for "flesh-eating", necrotizing fasciitis) are able to simultaneously bind to the MHC II molecule and T cell receptor molecule on the T cells. Binding to the receptor molecule does not involve specificity. This activates T cells 100 times the normal rate to bind to macrophages and T helper cells start secreting large amounts of interleukin-2 (IL-2) Excess IL-2 gets into the bloodstream and is transported around the body where it causes nausea, vomiting, fever, malaise and symptoms of shock The many different T cells that respond simultaneously to the superantigen, divide vigourously and many even die. Leaving the immune system deficient in those kinds of cells, and the host more prone to infections |
| Mucosal Immune System | the largest compnent of the immune system and a major entry for pathogens It consists of the entire gastrointestinal tract, urogenital tract, respiratory tract, and mammary glands A part of this is gut-associated lymphoid tissue (GALT) consisting of appendix, Peyer's patches of the small intestine, tonsils and adenoids GALT and the systemic immune system respond to pathogens differently n the gut M cells are interspersed between epithelial cells. These cells do not have microvilli on their surface. They take up antigens from the gut by endocytosis and release the antigens to antigen-presenting cells, such as dendritic cells beneath them Previously unactivated lymphocytes that become activated by antigen presenting cells are transported to other mucosal surfaces by entering the blood, via lymph nodes that drain from the intestinal region and thoracic region The primary immunoglobulin on mucosal surfaces, breast milk, and colostrum is IgA which can be secreted across epithelial cell |
| M cells | (or Microfold cells) are cells found in the follicle-associated epithelium of the Peyer's patch that have the unique ability to sample antigen from the lumen of the small intestine and deliver it via transcytosis to antigen presenting cells and lymphocytes located in a unique pocket-like structure on their basolateral side. M cells differ from normal enterocytes in that they do not have microvilli on their apical surface, but broader microfolds that give the cell its name. The filamentous brush border glycocalyx, an extracellular polysaccharide layer found throughout the intestine attached to enterocytes, is much thinner or absent on M cells. M cells are exploited by several pathogens, including Shigella flexneri, Salmonella typhimurium, and Yersinia pseudotuberculosis, as a way to penetrate the intestinal epithelium. Factors promoting the differentiation of M cells have yet to be elucidated, but they are thought to develop in response to signals from immune cells found in the developing Peyer's patch. |
| Factors modifying the immune system | Disorders/injuries environment lifestyle age |
| Comprised host | an individual with reduces resitance |
| Active immunization | administration of vaccines or toxoids |
| Vaccine | substance that contains an antigen that triggers immune response. Antigens can be derived from living but attenuated (weakened) organisms, dead organisms or parts of organisms. |
| Toxoid | an inactivated toxin that is no longer harmful but it retains its antigenic properties |
| Longevity of immunity | Vaccines made with live organisms (eg. measles (both rubella and rubeola) vaccines and oral polio confer longer-lasting immunity than those with dead organisms (intramuscular polio and typhoid fever vaccines; 3 to 5 yrs) or parts of organisms or toxoids ( tetanus and diphtheria toxoids- 10 yrs). |
| Can active immunity be used to prevent a disease after exposure? | no |
| Passive immunization | ready made antibodies are introduced into an unprotected individual. It is only temporary; depends on the titer of circulating antibodies. Immunization is established by administering a preparation such as gamma globulin, hyperimmune serum or an antitoxin that contains large numbers of antibodies Specificity and degree of this form of immunization depend on antibody type and concentrations used |
| Immune serum globulin (also known as gamma globulin) | consists of pooled gamma globulins from many individuals. Contains sufficient antibodies to provide immunity to a number of common disease, such as mumps, measles and hepatitis A. If donors are specially selected, gamma globulins that have high titers of antibodies can be prepared.Such preparations are often called hyperimmune sera. |
| Antisera | Blood products |
| Antitoxins | antibodies against specific toxins, such as those that cause botulism, diphtheria, or tetanus |
| Passive Immunity | gives immediate immunity to a nonimmune person who is exposed or it at least lessens the severity of the disease process. This is also used to counteract the effects of snake and spider bites |
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