Host Defense Mechanisms
Explain the origin of diversity of lymphocyte receptors.
-The par lymphocytes play in immune surveillance and recognition emphasizes the essential role of their markers. These markers are even more frequently called receptors, a name that emphasizes that their major role is to "accept" or "grasp" antigens in some form. Antigen molecules are diverse; there are potentially billions of unique types. The many sources of antigens include microorganisms as well as an endless array of chemical compounds in the environment
What are the main components of T-cell response?
-a T-helper cell activated in this way can help activate B-cells -mature T-cells in lymphoid organs are primed to react with antigens that have been processed and presented to them by an antigen-presenting cell, T-cells only recognize an antigen when it is presented in association with an MHC (major histocompatability complex) carrier -T-cells with CD4 receptors recognize peptides presented on MHC-II, and T cells with CD8 receptors recognize peptides presented on MHC-I -activated T-cells transform in preparation for mitotic divisions, and they differentiate into one of the subsets of effector cells and memory cells that can respond quickly upon subsequent contact
List components of the human immune system.
-a healthy functioning immune system is responsible for surveillance of the body, recognition of foreign material, and destruction of entities deemed to be foreign -the cells of the immune system constantly move about the body searching for pathogens while white blood cells (self) identify invading bacteria as nonself -the immune system evaluates cells by examining certain molecules on their surfaces called markers which allow the cells of the immune system to identify whether or not a newly discovered cell poses a threat -among the body compartments (intracellular, extracellular, lymphatic, cerebrospinal, circulatory) that participate in immune function are the mononuclear phagocyte system, the spaces surrounding tissue cells that contain extracellular fluid (ECF), the bloodstream, and the lymphatic system
Explain the difference between active and passive immunization.
-active immunity occurs when an individual receives an immune stimulus (antigen) that activates the B and T cells, causing the body to produce immune substances such as antibodies. Lasts for a relatively long time, sometimes for life. -passive immunity occurs when an individual receives immune substances (usually antibodies) that were produced actively in the body of another human or animal donor. The recipient is protected for a short time, even though he or she has not had prior exposure to the antigen
What is lysozyme and what is its role in host defense against microorganisms?
-an additional defense in tears and saliva is lysozyme, an enzyme that hydrolyzes the peptidoglycan in the cell wall of bacteria
What are the benefits of fever as a part of innate immunity?
-an important systemic component of inflammation -and innate immunity in general- is fever, defined as an abnormally elevated body -fever inhibits multiplication of temperature-sensitive microorganisms, fever impedes the nutrition of bacteria by reducing the availability of iron, fever increases metabolism and stimulates immune reactions and naturally protective physiological processes
What are antigens?
-any substance that stimulates the immune system to produce antibodies -antibodies are proteins manufactured by the body that help fight against foreign substances called antigens -an antigen is a substance that provokes an immune response in specific lymphocytes
What is inflammation?
-at its most general level, inflammatory response is a reaction to any traumatic event in the tissues -rubor (redness) is caused by increased circulation and vasodilation in the injured tissues, calor (warmth) is the heat given off by the increased flow of blood, tumor (swelling) is caused by increased fluid escaping into the tissues, and dolor (pain) is caused by the stimulation of nerve endings
List the components of the three lines of host defense against microorganisms.
-in the battle against all sorts of invaders, microbial and otherwise, the body erects a series of barriers, sends in an army of cells, and emits a flood of chemicals to protect tissues from harm. -the first line of defense includes any barrier that blocks invasion at the portal of entry -the second line of defense is an internalized system of protective cells and fluids that includes inflammation and phagocytosis -the highly specific third line of defense is acquired on an individual basis as each foreign substance is encountered by white blood cells called lymphocytes (long-term immunity)
What is the role of interferons in an immune response?
-interferon (IFN) is described as a small protein produced naturally by certain white blood and tissue cells and it is used in therapy against certain viral infections and caner -IFNs can inhibit the expression of cancer genes and have tumor suppressor effects -interferon is not virus-specific, so its synthesis in response to one type of virus will also protect against other types -interferons are important cytokines that activate or guide the development of white blood cells
Explain the role of components of the lymphatic system (lymph, lymphatic vessels, and lymphoid organs and tissues).
-lymph is a plasmalike liquid carried by the lymphatic circulation, it is formed when certain blood components move out of the blood vessels into the extracellular spaces and diffuse or migrate into the lymphatic capillaries and transports white blood cells, especially lymphocytes -lymphatic vessels is a system of vessels that transports lymph and is constructed along the lines of blood vessels, the thinnest vessels, lymphatic capillaries, can permeate all parts of the body and certain organs and is easily permeated by extracellular fluid that escaped from the circulatory system -other organs and tissues that perform lymphatic functions are the thymus, lymph nodes (glands), spleen, and clusters of tissues that appear in the mucosal surfaces (MALT)---all have a loose connective tissue framework that houses aggregations of lymphocytes -thymus originates in embryo and thymic hormones develop specificity in thymocytes and are released into circulation as mature T-cells -lymph nodes filter out materials that have entered the lymph and provide appropriate cells and niches for immune reactions -spleen filters blood for worn-out RBCs and pathogens then destroying them by resident macrophages -MALT provides immune functions against intestinal pathogens and produces some type of antibodies
What are blood cells that can destroy microorganisms through phagocytosis?
-monocytes are the largest white blood cells and include macrophages -they break down cells as well as other pathogens by phagocytosis
Explain the difference between natural and artificial immunity.
-natural immunity encompasses any immunity that is acquired during the normal biological experiences of an individual rather than through medical intervention -artificial immunity is protection from infection obtained through medical procedures. This type of immunity is induced by immunization with vaccines or the administration of immune serum
Should we use medications to reduce fever below 101.5*F? Explain.
-no because a fever of 101.5*F is considered a low grade fever -some advocates feel that a slight to moderate fever in an otherwise healthy person should be allowed to run its course in light of potential benefits and minimal side effects
Describe only the mains steps in activation of T-cells.
-now that the antigen is presented on the surface of the APC (antigen presenting cell), these cells are ready to activate T-cells bearing CD4 markers. CD4 T-cells are called the T-helper class; they bear an antigen-specific T-cell receptor that binds to the antigen (epitope) held by the MHC (major histocompatibility complex) molecule. At the same time the T-helper cell's CD4 marker also binds to the MHC (major histocompatibility complex) molecule. Once identification has occurred, the APC (antigen presenting cell) activates this T-helper cell. The T-helper cell, in turn, produces a cytokine, interleukin-2 (IL-2), which is a growth factor for T-helper cells and cytotoxic T-cels. -CD4 is an accessory receptor protein on T helper cells that binds to MHC class I molecules, and recognize peptides presented on MHC-II
Explain roles of the major histocompatibility complex and lymphocyte receptors (immunoglobulins and T-cell receptors) in immune response.
-one set of genes that codes for human cell receptors is the major histocompatability complex (MHC). This gene complex gives rise to a series of glycoproteins (called MHC molecules) found on all cells except red blood cells. The MHC is also known as the human leukocyte antigen (HLA) system. This marker complex plays a vital tole in recognition of self by the immune system and in rejection of foreign tissue. -the part lymphocytes play in immune surveillance and recognition emphasizes the essential role of their markers. These markers are even more frequently called receptors, a name that emphasizes that their major role is to "accept" or "grasp" antigens in some form.
What is immunity?
-the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells
Explain activation of B-cells in an immune response.
-the activation of B-cells by most antigens (T-dependent antigens) involves a series of events: (1) binding of antigen, (2) antigen processing and presentation, (3) B-cell/T-helper cell cooperation and recognition, (4) B-cell activation, (5) differentiation, (6) clonal expansion
Describe the process of phagocytosis (pay attention to the role of chemotaxis, different receptors, and lysosome in this process).
-the activities of phagocytes are to survey the tissue compartments and discover microbes, particle matter, and injured of dead cells, to ingest and eliminate these materials, and to recognize immunogenic information (antigens) in foreign matter -phagocytosis occurs in steps: chemotaxis, ingestion, phagolysosome formation, destruction, and excretion
How does the complement contribute to the host defense against microorganisms?
-the complement system, named for its property of "complementing" immune reactions, consists of over 30 blood proteins that work together to destroy bacteria and certain viruses
What is complement?
-the immune system has another complex and multiple-duty system called complement
What is the role of inflammation as a part of innate immunity?
-the innate immune system is made of defenses against infection that can be activated immediately once a pathogen attacks -the inflammatory response actively brings immune cells to the site of an infection by increasing blood flow to the area
What is the role of keratin in the first line of defense?
-the outermost later (stratum corneum) of the skin is composed of epithelial cells that have become compacted, cemented together, and impregnated with an insoluble protein- keratin -the result is a thick, tough later that is highly impervious and waterproof -few pathogens can penetrate this unbroken barrier, especially in regions such as the soles of the feet or the palms of the hands
Describe the ways how antibodies can contribute to elimination of invading microorganisms.
-the principal activity of an antibody is to unite with, immobilize, call attention to, or neutralize the antigen for which it was formed -antibodies called opsonons stimulate opsonization, a process in which microorganisms or other particles are coated with specific antibodies so that they will be more readily recognized by phagoctyes, which dispose of them. -agglutination makes microbes immobile and enhances their phagocytosis. The interaction of an antibody with complement can result in the specific rupturing of cells and some viruses -in neutralization reactions, antibodies fill the surface receptors on a virus or the active site on a microbial enzyme to prevent it from attaching normally -an antitoxin is a special type of antibody that neutralizes bacterial exotoxins -antibodies may also function to kill targets by inducing production of H2O2 and ozone
What is presentation of antigens and where does it occur? What immune cells are involved in this process?
-the property of behaving as an antigen is called antigenicity. To be perceived as an antigen or immunogen, a substance must meet certain requirements in foreignness, shape, size, and accessibility -most materials that serve as antigens fall into these chemical categories: proteins and polypeptides, lipoproteins, glycoproteins, nucleoproteins, polysaccharides and lipopolysaccharides -happens on the surface of an antigen presenting cell (APC)
Explain the process of clonal selection.
-the second stage of development- clonal selection and expansion- happens after exposure to the correct antigen such as a microbe. When this antigen enters the immune surveillance system, it encounters specific lymphocytes, ready to recognize it. Such contact stimulates that clone to undergo mitotic divisions and expands it into a larger population of lymphocytes, all bearing the same specificity -two important facts about the phenomenon of clonal selection are that (1) lymphocyte specificity is preprogrammed, existing in the genetic makeup before an antigen has ever entered the tissues; and (2) each genetically distinct lymphocyte expresses only a single specificity and can react to only one type of antigen
Describe components of the first line of defense.
-these defenses are a normal part of the body's anatomy and physiology -these inborn, nonspecific defenses are either physical or chemical barriers that impede entry of not only microbes but also any foreign agent whether living or not -the skin and mucous membranes of the respiratory and digestive tracts have several built-in defenses
Explain classification of white blood cells and the role of the main classes.
-white blood cell lines are programmed to develop into several secondary lines of cells during the final process of differentiation, these committed likes of WBCs are largely responsible for immune function -WBCs are divided into two groups, granulocytes and agranulocytes -the types of granular leukocytes present in the bloodstream are neutrophils, eosinophils, and basophils -main work of neutrophils is production of toxic chemicals and in phagocytosis at the early stages -eosinophil granules contain peroxidase, lysozyme, and other digestive enzymes, as well as toxic proteins and inflammatory chemicals. Eosinophils attack and destroy large eukaryotic pathogens and are involved in formation of fetal tissue and inflammation and allergic reactions -basophils contain granules with potent chemical mediators and have functional similarities with mast cells. Mast cells are first-line defenders against local invasion of pathogens, recruit inflammatory cells and responsible for the release of histamine and other allergic stimulants -the two general types of argranulocytes are lymphocytes and monoctyes -three main types of lymphocytes: B cells, T cells, and null cells -B cells mature in special bone marrow sites, T cells mature in the thymus, both transported through the bloodstream and lymph moves freely -null cells, chief among them natural killer (NK) cells, develop from lymphoid stem cells and can act with the specific immune response or independently -monocytes are discharged by bone marrow into the bloodstream where they live as phagocytes for a few days then leave circulation to undergo final differentiation into macrophages -macrophages are responsible for specific and nonspecific phagocytic and killing functions, processing foreign molecules and presenting them to lymphocytes, and secreting biologically active compounds that assist, mediate, attract, and inhibit immune cells and reactions
