z-MicroBio Final – Ch. 29, 30 – Flashcards
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| Virulence of Microorganisms -vs- Resistance of Host |
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| Virulence: Invasiveness Toxigenicity Resistance: Acquired or Induced Immunity (Resistance) Humoral Immunity: mediated by antibodies Cellular Immunity: mediated by cells (T cells) Natural Resistance: (Innate immunity) Cells: macrophages, etc. Mechanical barriers: skin & mucous membranes Chemical factors: intereferons, fatty acids on skin Microbial factors |
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| Innate Immunity (Natural Resistance)Non-Specific |
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| Mechanical Barriers, Chemical factors, Microbial factors, Cellular factors [image] |
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| Mechanical Barriers |
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| Skin: very few microorganisms penetrate Mucous membranes: mucous traps many airborne bacteria; coughing/sneezing expel a portion of the microbe-laden mucous into the atmosphere, the rest are carried into the stomach were high acidity and digestive enzymes kill many microbes Found in nasal-pharyngeal region and the upper respiratory tract and intestinal epithelium[areas open to outside] Much more susceptible to penetration than the unbroken skin Chemical or physical damage of mucous membranes increases the chance of infection and disease Tears: flushing of eyes (contains lysozymes) Respiratory tract: ciliated epithelium lines walls; cilia, beating upward, push bacteria, mucous and other particulate material upward to where it is expelled in saliva & nasal secretions |
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| Chemical factors |
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| Fatty acids: attack gram-negative on skin surface Bile salts in gall bladder, liver, intestines inhibit gram-positive Lysozyme in tears and saliva; more effective against gram-positive Phagocytins in leucocytes (wbc) Complement: microbial cell membranes and some cancer cells can lose physical integrity and lyse in presence of complement. Interferon: active against viruses |
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| Microbial factors |
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| Normal flora of the body provides protection by competition with pathogens; ex: gram + making fatty acids on the skin If damaged by antibiotics, the individual may get a fungal infection |
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| Cellular factors |
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| Phagocytic cells may engulf microorganisms and destroy it. |
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| Phagocytes |
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| On rare occasions, pathogens break through the physical and chemical defenses. One of the first cells that they encounter are class of cells called phagocytes (literally: cell that eats) The primary function of phagocytes is to engulf and destroy pathogens. In some cases, phagocytes can act as antigen-presenting cells (APCs) and generate a peptide antigen (s) that will activate specific immune responses 3 Main: Neutrophils (polymorphonuclear leukocytes), monocytes, macrophages Neutrophils: actively motile granulocytes containing large #s of lysosomes |
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| Major Immune Cell Types |
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| a. Nucleated cell in lower left is neutrophil segmented nucleus granular cytoplasm a. Monocyte: slightly above and to right B. Circulating lymphocyte: no visible cytoplasm. Phagocytes employ a variety of chemical processes designed to destroy the pathogen: (hydrogen peroxide, lysozyme, proteases, phosphatases, nucleases, lipases) Not to be outdone, some pathogens have mechanisms to kill or avoid phagocytes Ex: Staphylococcus aureus: Carotenoids which quench singlet oxygen and prevent killing[also Staph. Has coagulase that walls it off and prevents phagocytosis. Macobacterium tuberculosis: grow and persist in the macrophage |
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| Induced Immunity |
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| Requires prior contact or exposure to antigen Humoral Immunity Cellular Immunity |
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| Humoral Immunity |
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| mediated by antibodies produced by B-lymphocytes that differentiate into plasma cells that produce antibody. Antibodies B cells (lymphocytes) -> plasma cells -> Ab |
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| Cellular Immunity |
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| mediated by cells; Ex. Cytotoxic T-cells T Cells (lymphocytes) -> Activated T-Lymphocytes |
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| T-Cells |
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| CD4: T-helper (TH1 and TH2): helps or induces an immune response; Associated with MHC Class II CD8: T-cytotoxic cells; associated with MHC class I |
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| Characteristics of specific immunity |
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| Specificity Memory: Capacity to respond more quickly and vigorously after exposure to an antigen Tolerance: acquired inability to make an immune response to certain antigens [image] [image] [image] [image] |
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| Innate immunity |
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| results from interactions between pathogen-associated molecular patterns (PAMPS) found as cell surface components and pattern recognition molecules (PRMs) found on phagocytes. PRMs first observed in Drosophila, called Toll receptors Toll-like receptors on human phagocytes recognize specific PAMPS (Ex. TLR-4, a PRM on human phagocytes recognizes & responds to interactions with LPS, a PAMP in outer membrane of gram negative. Interaction of a PAMP with the phagocyte PRM triggers a trans-membrane signal that results in transcription of a number of cell proteins in phagocyte. This transcriptional activation leads to production of toxic oxygen compounds that lead to pathogen death. See diagram: H2O2; O2-; HOCl; NO; OH.; 1O2 |
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| Adaptive Immunity |
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| Adaptive immunity: due to antigen specific T cells, resulting in two distinct effector pathways II. Antibody mediated immunity: results from soluble antigen-specific antibody proteins, products of antigen stimulated B lymphocytes. III. Cell-mediated immunity: mediated by antigen specific T cells Antibody mediated (humoral immunity) results from soluble antigen-specific antibody proteins, products of antigen-stimulated B lymphocytes Cell mediated (cellular immunity) mediated by antigen specific T cells. |
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| Origins of Immune Response |
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| Lymphoid precursor can generate T & B cells Myeloid precursor can generate Monocytes which in turn develop into macrophages or dendritic cells that are phagocyte cells involved in antigen uptake and display. Granulocytes: including neutrophils, mast cells, esinophils, and basophils. Neutrophils are also phagocytes. The others release their granule contents in reponse to pathogens, pathogen products, or damaged host cells. [image] |
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| Acquired Immunity |
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| Acquired immunity (a state of altered responsiveness to a specific substance induced by prior contact with the “foreign” substance) Anamnestic: has memory; repeated contact with antigen amplifies response Immunogens: Usually protein or complex polysaccharides (molecular complexity) Nucleic acids, simple polysacchrides, & lipids are poor immunogens, because composed of repeating monomers. High molecular weight: >10,000 Appropriate physical form: Large, complex macromolecules in insoluble or aggregate form (example proteins precipitated by heating) are good immunogens. Insoluble readily taken up by phagocytes, leading to immune response. Foreign to responder Note: Epitopes recognized by antibody Antibody: Plasma synthesized in humoral response which are capable of combining with the provoking antigen 5 classes Fab & FC portions |
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| Immunogen |
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| substance capable of eliciting an immune response. An antigen may or may not be an immunogen Antigens are substances that react with antibodies or TCRs (T cell receptors) |
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| Hapten |
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| Low molecular weight substance which can not act as an immunogen by itself. When attached to high molecular weight materials, an antibody response is made to the carrier (the high molecular weight material), as well as to the hapten. Next time hapten enters it acts as antigen and can react with those antibodies made to its epitope (s). |
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| Antigen Binding by Antibodies and T-Cells |
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| Antibody or TCR does not interact with the antigenic macromolecule as a whole, but with distinct portions of the molecule called the epitope. Ab specificity is sensitive enough to distinguish between two very similar epitopes; Ex. Glucose from Galactose which only differ in the orientation of a -OH group [image] |
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| Antigen Binding by T-Cells |
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| While antibodies generally recognize epitopes expressed on macromolecular surfaces, T-Cell receptors (TCR’s) recognize determinates only after the immunogens have been partially degraded. The degraded or “processed” antigen is presented to T cells on the surface of specialized anti-presenting cells (APCs) or target cells. |
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| Antigen Presentation to T-Cell |
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| [image] |
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| MHC PROTEINS |
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| major histocompatibility complex Function as antigen presenting molecules and interact with both antigen and TCR T cell cannot recognize foreign antigen unless it is presented in context of an MHC protein. Two Classes Class I: found on surface of all nucleated cells; proteins made and assembled in ER. Protein antigens manufactured within the cell [ex from viruses or tumors] are degraded in proteosome in the cytoplasm, transported across ER through a pore formed by TAP proteins, bind to Class I, transported to cell surface to bind with TCR [CD8 co-receptor makes binding stronger]; then, Tc cell releases cytokines and cytotoxins to kill target cell. Class II: found only on surface of B lymphocytes,macrophages and dendritic cells, all dedicated APCs MHC II proteins;produced in ER and assembled with a blocking protein (Ii, invariant chain); goes to phagolysozome; Ii and foreign proteins [imported from outside the cell by endocytosis] are digested. Class II then binds to digested proteins, complex tranported out of cell to bind to TCR & CD4 coreceptor on TH cell,. TH release cytokines that act on other cells to activate immune response. |
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| T Cells |
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| T-Cytotoxic Cells (Tc): destroys cells that display antigens embedded in MHC class-I molecules CD8 Uses perforin to lyse the infected cells Uses granzymes (proteins) that cause apoptosis Viruses [image] |
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| THelper cells(TH1 and TH2) |
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| Macrophages: central role as APCs: bind, process, and present AG to TH cells. T-inflammatory (TH1)cells, are activated by antigens presented on macrophages in the context of MHC Class II protein. TH1 cells then produce cytokines that stimulate macrophages to take up and kill certain foreign cells by themselves Activated macrophages can kill intracellular bacteria that would normally multiply TH2 cells: key role in B cell activation & AB production. [image] [image] |
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| Antibodies (Immunoglobulins |
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| Antibodies, or immunoglobulins (Ig) are protein molecules that able to combine with antigenic determinates. Found in the serum and in other body fluids such as gastric secretions and milk Serum containing antigen-specific antibody is often called anti-serum Comprised of 5 major classes on the basis of their physical, chemical, and immunological properties; IgG, IgA, IgM, IgD and IgE About 80% of the serum Igs are IgG proteins |
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| Immunoglobulins |
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| All immunoglobulin classes have VH (variable heavy) and VL (variable light) domains that bind antigens. All immunoglobulin classes have Constant domains. It is the difference in the amino acid sequence of the constant domain that defines the class of immunoglobulin molecule; gamma (), alpha (), mu (), delta () or epilison () FC , FAB [image] |
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| IgG |
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| Most common of the circulating antibodies Composed of 4 polypeptide chains. Interchain disulfide bridges (S-S) connect the individual chains A functional IgG molecule consists of two antigen binding sites. IgG is therefore bivalent and can bind two identical epitopes Crosses the placental barrier [image] |
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| IgM |
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| Usually found as an aggregate of five immunoglobulin molecules attached by at least one “J” chain Every heavy chain of IgM contains a fourth constant domain (CH4) 1st class of immunoglobulin made in a typical immune response to a bacterial infection 10 binding sites Low affinity but high avidity [image] |
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| IgA |
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| Present in the serum in the monomeric form, but in secretions it is a dimer. colostrum, gastrointestinal secretions, and mucus secretions of respiratory and genitourinary tracts [image] |
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| IgE |
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| Found in serum in very small amounts. Mediates Immediate-type hypersensitivities (allergies) Like IgM, IgE has a fourth constant domain Constant region functions to bind IgE to MAST cells surfaces (more on MAST cells later) |
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| IgD |
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| Present in serum in low concentrations Has no know function Abundant on surfaces of B cells and plays a role along with monomeric IgM in binding antigen to B cells |
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| Introduction of antigen |
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| Antigens are spread via lymphatic and blood circulatory systems to neighboring secondary lymphoid organs (lymph nodes, spleen, or mucosal-associated lympoid tissue (MALT). Intervenously injected antigen travels via blood to spleen, where antibodies are formed. Subcutaneously, intradermally, topically, or intraperitoneally introduced antigens are carried by lymphatic system to the nearest lymph node. Antigens introduced to mucosal surfaces (ex. Mouth) are delivered to the GALT lining the intestinal tract resulting in antigen-specific IgA antibody production in the gut. |
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| Primary Response |
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| Following initial antigen introduction, each antigen-stimulated B cell multiplies and differentiates to form both antibody-secreting plasma cells, and memory cells Plasma cells are short-lived (< 1 week) but produce large amounts of IgM antibody in this primary antibody response. Following a latent period, specific antibodies show up in blood, followed by a gradual increase in antibody titer (quantity), and then a slow fall in the primary response. |
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| Secondary Response |
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| Memory cells generated by the initial exposure to antigen may live for several years. Upon re-exposure to the immunizing agent memory cells need no T cell activation; they quickly transform to plasma cells and begin producing IgG The antibody titer rises rapidly to a level 10-100 greater than the titer following the initial exposure The rise in antibody titer is referred to as the secondary antibody response The secondary response is characterized by a switch from IgM to IgG production (class switching) Over time titer slowly decreases but a later exposure can cause another secondary response. This forms the basis for booster shots |
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| Summary of Antibody Production |
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| [image] |
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| Two Divisions of Immune Response |
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| Humoral-antibodies B lymphocytes differentiate into plasma cells and produce antibody. Mediated by B lymphocytes (mature in bone marrow) Ex. Chickens - Remove Bursa & they fail to produce antibodies and become susceptible to bacterial or extrinsic invaders Ex. Humans - Burton’s Agammaglobulinaemia- Children fail to produce antibody. Humans do not have a bursa, but instead have GALT (gut associated lymphoid tissue) and MALT (mucosal cells that line external surfaces) In both of the above examples, cellular immunity remains intact and they are more susceptible to bacterial infections rather than viral or intrinsic. Cellular Mediated by cells; involve lymphocyte processing by thymus and involve activated T cells. Where Ab mediated (humoral) recognizes substances that are outside host cells (extrinsic), cell-mediated immune response is effective in recognizing modified host cells; thus it is important in controlling infections in which pathogens can reproduce within living cells (ex. Viruses, some bacteria such as rickettsia & chlamydia, some parasitic protozoans like typanosomes. Also important in surveillance/destruction of malignant Cell mediated immune responses also include: Delayed hypersensitivity in response to intracellular bacteria like Mycobacterium tuberculosis and fungal infections such as Histoplasma capsulatum. Cytotoxic T lymphocyte responses to virally infected cells Response to tumor cells and tissue grafts by natural killer cells |
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| Cellular - experiments and nature |
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| Thymectimized mice- Susceptible to viral infections or intrinsic parasites like M. tuberculosis Increased rate of tumor production Failure to reject transplanted tissue Di George’s Syndrome (humans) Infants lacking a functioning thymus gland (equivalent to thymectimized mice above) a, b, & c above apply 25,000 times greater chance of malignancy but not susceptible to bacterial “extrinsic” infection |
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| immunosupressive |
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| drugs or if chemicals are present (pollutants, drugs, radiation, UV, cigarette smoking, insecticides, etc), or in old age |
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| Attenuation |
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| Attenuated strains have lost virulence Often they retain immunogenicity; therefore, may be used for production of vaccines; especially viral vaccines: measles, mumps, e.t.c Laboratory cultivation typically results in a decrease in virulence of pathogens or even a complete loss |
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| Nosocomial Infections |
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| Many hospital patients with noninfectious diseases (ex. cancer and heart disease) acquire microbial infections that produce disease because they are compromised. Such health-care associated infections are called nosocomial infections. Procedures like catheterization, hypodermic injection, spinal puncture, biopsy and surgury unintentionally introduce microbes into patient. |
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| Control of Microorganisms |
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| Physical Agents Most widely used is heat Chemical Agents Called Antimicrobial Agents Kill or Inhibit Growth Sterilization: treatment that frees the treated object of all living organisms, including viruses. Death: defined as irreversible loss of ability to reproduce when inoculated into an appropriate medium or host. |
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| Autoclave |
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| An autoclave permits application of steam heat under pressure at temperatures above the boiling point of water, killing endospores. At 15 lbs per sq inch above normal atmospheric pressure water boils at 121oC. At that temperature for 15 minutes, endospores are killed if volume of liquid not too large. Ex. it takes 30 min for 2000mL flask. |
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| Pasteurization |
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| Pasteurization does not sterilize liquids but reduces microbial load, killing most pathogens and inhibiting the growth of spoilage microorganisms. Originally 30 min at 62o C Now: Flash Pasteurization: 72o C, 15 sec. |
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| Ultraviolet Light |
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| Most effective at 260 nm |
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| Ionizing Radiation |
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| Higher energy and shorter wavelength |
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| Membrane Filter Sterilization |
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| lab |
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| Antimicrobial Agents |
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Antimicrobial agent is a natural or synthetic chemical that kills or inhibits growth of microorganisms. Kills: cidal (viricidal, fugicidal, bactericidal) lysis: bacteriolytic Inhibits growth: static (bacteristatic) MIC Two classes: Invitro and Invivo In vitro: Disinfectants: chemicals that kill microorganisms but not necessarily spores Sanitizers: reduce to safe levels Antiseptics or germicides: kill or inhibit growth but nontoxic enough to be applied to human tissue. |
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| Agar Zone Diffusion |
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| Zones of inhibition |
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| Tube Dilution Test |
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| MIC: minimum inhibitory concentration: in lab |
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| Bactericidal Tests |
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| transfer to medium without agent and test for growth Phenol Coefficient Test Greatest dilution that kills microorganism at 10 minutes but not 5 to greatest dilution of phenol that kills microorganism in 10 but not 5 minutes. [image] |
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| Antibiotics |
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| chemical substance produced by one microorganism that kills or inhibits growth of another. (Ex Penicillin G) Effective against gram +: gram - impermeable |
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| Synthetic Antimicrobial Agents |
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| sulfanilamide [image] |
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| Semisynthetic |
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| other penicillins: modify R group. |
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| Ideal Properties |
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| Selective Toxicity Toxic to Microorganisms but not harmful to man and higher animals. Diffuses to site of infection Very few toxic side effects Allergic reactions not common |
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| Penicillin |
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| [image] |
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| Antifungal Drugs |
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| Antifungal agents (Table 20.6) fall into a wide variety of chemical categories. Because fungi are Eukarya, selective toxicity is hard to achieve, but some effective chemotherapeutic agents are available. [image] |
