Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
50 Cards in this Set
- Front
- Back
|
Q: Are neutrophils necessary for survival?
|
-Most individuals with defects in neutrophil function die before puberty. Furthermore, medically induced granulocytopenia is a problem. Anti-mitotic chemotherapy of cancer can block neutrophil production.
|
|
|
Q: Are neutrophils susceptible to antimitotic agents?
|
-Neutrophils are uniquely susceptible to antimitotic agents because of their short life spans. Neutrophils have to be constantly replenished. Their half life in blood is 6-7 hours and then survival in tissues is 1-2 days. Then they die. Transfusions of neutrophils are impractical because of neutrophil fragility and their short life span. When the neutrophil blood count falls below 500 cells per ul (mm3), patients are prone to life-threatening infections
|
|
|
Q: What is the function of neutrophils?
|
-Neutrophils kill bacteria and yeast by phagocytosis followed by two enzymatic pathways that work together to kill the bacteria. Both pathways are necessary. For many years, it was thought that each pathways was separately toxic, an oxidative pathway and a nonoxidative pathway. Today it is thought that the oxidative pathway (which normal takes place only inside the vesicles) may be actually nontoxic by itself, It is currently thought that the oxidative pathway serves to increase the salt concentration (osmolarity) in the vesicles, to promote the anti-microbial activity of the non-oxidative enzymes
|
|
|
Q: What does phagocytosis require?
|
-Phagocytosis requires specific rector-ligand interactions (such as IgGReceptor- IgG and complement receptors-C3b) and results in engulfment of intact live bacteria or yeast cells. After engulfment, phagolysosomes form where bacteria and yeast are killed and then digested.
|
|
|
Q: Describe opsonins function and give examples of Igs and complements that function as this.
|
-IgG and C3b/iC3b function as opsonins
-The neutrophils recognize these opsonins bound to the bacteria and yeast. Neutrophils use FCgamma receptors to bind IgGl and IgG3. (These two IgG subclasses are also the same subclasses that fix complement well.) Neutrophils also use receptors for complement proteins, the CRl receptor for complement C3b and the CR3 receptors for iC3b. (The complement protein C3b becomes coupled covalently to the surfaces of the pathogens as a result of all 3 of the complement pathways.) |
|
|
Q: Describe the formation of a phagolysosome.
|
-During phagocytosis, the contents of lysosome-like primary granules are added to the phagosome to make a phagolysosome where the bacteria are killed by nonoxidative mechanisms and digested. The formation of phagolysosomes is step 4 of figure 2.
-Killing of the microbes occurs inside these vesicles. Superoxide production starts at the time of initial recognition of the pathogens. |
|
|
Q: What are the steps involved in the oxidative events?
|
1. The oxidative events start upon initial receptor-ligand interactions.
2. Oxidative events begin with the respiratory burst in which oxygen is consumed and superoxide anion is generated. 3. People with deficiencies in the oxidative burst suffer from Chronic Granulomatosus Disease. 4. The nonoxidative mechanisms of killing take place in the phagolysosome. 5. Phospholipase A aids in permeabilizing bacteria, generating detergent lysolecithins in membranes and probably allows toxins to enter the bacteria. Lastly, the neutrophil degrades the phagolysosomal contents to simple sugars, lipids and amino acids which are "defecated". |
|
|
Q: Describe step 1 of oxidative events.
|
-The major molecules produced by the oxidative process are the superoxide anion, hydrogen peroxide, hypochlorite, the hydroxyl radical, and singlet oxygen.
|
|
|
Q: Describe step 2 of oxidative envets.
|
-To generate this burst, upon natural stimulus with opsonized particles or in the laboratory with the synthetic peptide fMet-Leu-Phe, the neutrophil brings several different proteins together at the plasma membrane to form a catalytic oxidase unit. The cytochrome b558 is normally inside specific granules and is mobilized to the plasma membrane only during the oxidative burst. "Three cytoplasmic proteins also translocate to the neutrophil membrane to complete the oxidase unit. The oxidase complex reduces 02 to the superoxide anion, 02-. This burst is termed respiratory because oxygen is consumed. The burst is transient and stops shortly after the yeast or bacterial particles are ingested.
|
|
|
Q: Describe step 3 of oxidative events.
|
-The disease is usually fatal. The patients die of ordinary pyogenic (pus-forming) infections. Bacteria such as Staphyloccus aureus, Staphyloccus epididymus, Pseudomonas, and E. coli commonly cause pyogenic infections. Deficiency of the oxidative mechanism is detected by the nitroblue tetrazolium (NBT) test. Normally the dye is yellow and water soluble. After a normal oxidative burst, the dye is reduced to a blue, water insoluble dye called formazan.
|
|
|
Q: What do we know from patients with chronic granulomatus disease (CGD)?
|
-we know the complexity of the oxidative mechanisms. Each component of the oxidative burst must function. Components of the cytochrome b protein complex are needed to form the NADPH-dependent oxidase, a normal hexose monophosphate shunt, a normal glucose-6-P04 dehydrogenase, and a normal glutathione reductase (to keep the hexose monophosphate shunt working) are all needed. Genetic defects in anyone of these genes can lead to chronic granulomatous disease(s).
|
|
|
Q: Describe step 4 of oxidative events.
|
-Nonoxidative events mediate microbial killing and are essential important. These events take place at low pH initially and then at neutral pH., The phagolysosome becomes acidic, ranging between pH 4-6 within 5-12 minutes after ingestion.
|
|
|
Q: Why do nonoxidative events take place at a low pH?
|
-The low pH favors a "stomach-like" reaction in which enzymes with low pH optima chew up the outer carbohydrate and lipid coats of bacteria.
|
|
|
Q: What happens to the phagolysosome after low pH?
|
-The phagolysosome returns to neutral pH later and increases in salt concentration to support additional killing and the final degradation of the pathogen. The higher salt concentration activates many nonoxidative enzymes be releasing them from the proteoglycans of the granules to which they were bound. (When bound to the proteoglycans, these enzymes were unable to interact with their substrates.)
|
|
|
Q: Describe BPI (bactericidal permeability increasing) factor.
|
-is a very basic (cationic) protein of 59,000 m.wt. which kills Gram negative bacteria. It can kill bacteria in 15 seconds!
|
|
|
Q: Describe defensins.
|
-The defensins in human neutrophil primary granules are a set of four related small (4,000 m.wt.) toxic basic proteins which kill yeast and also kill bacteria. They comprise as much as 30% of the granules by weight. They are so basic, their isoelectric point is about pH 10. Their mechanism of action appears to be to poison selective ion pumps of the bacteria and yeast, causing electrolyte imbalances. The bacteria or yeast can be killed by defensins only when they are metabolically active and pumping ions.
|
|
|
Q: What does serine proteast cathepsin G do?
|
-kills bacteria
|
|
|
Q: What does phospholipase A do?
|
-aids in permeabilizing bacteria, generating detergent lysolecithins in membranes and probably allows toxins to enter the bacteria
|
|
|
Q: What are the two types of neutrophil granules?
|
-The two types of neutrophil granules, azurophilic or primary granules and specific or secondary granules, are named according to their time of synthesis. The primary granules are formed first and the secondary granules are acquired later. Both are formed during differentiation in the marrow. The primary granules have contents similar to the lysosomes of other cells, whereas the secondary granules are a distinct feature of neutrophils.
|
|
|
Q: What type of degradative enzymes do primary granules have that are effective at the initial low pH after ingestion?
|
-acid phosphatase which remove phosphates from nucleotides
-cathepsins B, D, etc., which are cysteine proteases active at low pH -myeloperoxidase which generates toxic hypochlorite from hydrogen peroxide and chloride ions in the phagolysosome -glycosidases that remove simple sugars from complex sugars -and lysozyme--breaks down sugar linkages of the bacterial cell walls. |
|
|
Q: What type of degradative enzymes do primary granules have that are effective at the neutral pH?
|
-serine proteases like cathepsin G, neutrophil elastase, and proteinase 3 neutrophil collagenase
-alkaline phosphatase -aryl sulfatase which can remove the sulfate from tyrosine sulfate -5'nucleosidase |
|
|
Q: What other enzymes do primary granules have that are not enzymes?
|
-defensins or small (4,000 m.wt.) toxic basic proteins (which kill yeast like Candida, and bacteria)
-BPl, bactericidal permeability increasing factor -sulfated proteolgycan which accounts for the azurophilic (blue) staining of the primary granules. |
|
|
Q: What is Chediak Higashi Disease?
|
-People with Chediak Higashi Disease has a defect in nonoxidative killing. They have a defect in the CHS 1 gene that encodes a lysosomal transporter protein, which is manisfest as a rare autosomal recessive disease. Chediak Higashi Disease is characterized by partial albinism (due to defective granules in melanocytes), agouti hair color (due to unusual granules that color hair), increased susceptibility to infections, decreased NK cell activity and abnormal giant granules in neutrophils. The lysosomal granules fail to fuse with the phagosomes inside neutrophils. The patients rarely survive past puberty, even with antibiotic therapies. The disease informs us of the importance of the nonoxidative mechanisms in neutrophil control of bacteria
|
|
|
Q: What are secondary granules?
|
-Secondary granules are the "specific" granules which are found only in (specific to) myeloid cell granules. Many of the proteins of specific granules are mobilized directly to the neutrophil plasma membrane upon a neutrophil's contact with bacteria. These proteins are either incorporated into the plasma membrane or released in close approximation of the C phagocytized particle.
|
|
|
Q: What are some examples of secondary granules?
|
-phospholipase A that generates the detergent lysolecithin that may kill bacteria
-lysozyme (Yes, lysozyme is found in both types of granules) -lactoferrin which promotes the enzymatic formation of the toxic hydroxyl radical -vitamin B12 binding protein. -Cytochrome b558, a membrane-associated protein essential for the catalytic unit that generates the oxidative burst. -extra fMet-Leu-Phe receptors and extra CR3 receptors that can be mobilized rapidly to fuse with the neutrophil cell membrane. -neutrophil collagenase, released as a proenzyme. |
|
|
Q: What are some properties concerning neutrophils?
|
-Neutrophils are one of 3 types of granulocytes or granular leukocytes-all have granules in cytoplasm. The granular leukocytes are termed neutrophils, basophils (blue), and eosinophils (Pink) based on Giemsa stains.
-Neutrophils are the most abundant white blood cells in circulation in blood, comprising about 70% of total leukocytes. Neutrophils are also "marginated" (attached in aggregates to blood vessel walls) and stored in the bone marrow. |
|
|
Q: Describe the amounts of neutrophils in the human body per kg.
|
-3.5 X 10^8 neutrophils in blood
-3.5 X 10^8 marginated neutrophils (released during exercise and by adrenalin -2.0 X 10^9 neutrophils in bone marrow to be released when needed |
|
|
Q: How long will it take for loss of neutrophil development in the bone marrow to be detected? How long will it take to replacd the neutrophils?
|
-Loss of neutrophil development in the bone marrow will be undetectable for almost a week after their development is arrested. Once neutrophil deficiency is observed and their development is reinstated, it will take almost 2 weeks to replace the lost neutrophils. The extremely short plasma and tissue half lives of neutrophils mean that, when mitosis is blocked, these cells will later disappear from circulation. Since neutrophils take 4-6 days of mitosis to expand from committed stem cells and 5-7 days to mature in the bone marrow, their loss (measured from blood samples) may not be detected until 5- 7 days after mitosis is arrested. The long bone marrow maturation time of these cells contributes to the need for careful and frequent• monitoring of neutrophil counts to avoid severe neutropenia in cancer chemotherapy.
|
|
|
Q: What types of cells do the polymorphonuclear cells share their bone marrow progenitor cells with?
|
-Polymorphonuclear cells share common bone marrow progenitor cells with monocytes
|
|
|
Q: What are the steps involved that neutrophils take to reach site of infection?
|
-Neutrophils transit from blood to the site of infection in several steps, including inflammatory adherence to blood vessels, emigration through the vessels, and chemotaxis
|
|
|
Q: What mediates neutrophil adherence to blood vessels or margination?
|
-selectin and integrin proteins
|
|
|
Q: Describe selectins.
|
-Selectins are lectins (proteins that bind specific sugars) and are found on both the neutrophil and the blood vessel endothelium. There are three selectins which direct leukocyte cell traffic. L-selectin is constitutively found on neutrophils. P-selectin is preformed, sequestered in vesicles inside endothelial cells, and popped out to join the endothelial cell plasma membrane after induction, E-selectin is made de novo after inflammatory stimuli.
|
|
|
Q: Describe integrins.
|
-Integrins are plasma membrane proteins that allow different types of cells to blind to each other. Integrins are formed by pairs of one alpha chain integrin combined with one beta chain integrin. There are many different alpha interim chains and many different beta integrins. There are many different alpha-beta integrin combinations that occur and several of the them bind to common ligands (but at different places within the ligand.)
|
|
|
Q: What stimulates neutrophils to migrate?
|
-Neutrophils (and macrophages) migrate in response to a gradient of chemotactic factors, including chemotaxins and chemokines.
-Chemokines are chemotactic cytokines. They are secreted by cells and are therefore cytokines. In contrast, other chemotactic factors are either generated from plasma proteins (C5a) or are not proteins (leukotriene B4). |
|
|
Q: What is chemotaxis?
|
-Chemotaxis is directed movement towards the site of the chemotaxin. Chemokinesis is the nondirectional movement of neutrophils. Neutrophils squeeze through the walls of the blood vessels in a process called diapedesis.
|
|
|
Q: What are chemoattractants?
|
-Bacterial proteins are also chemoattractants, stimulating neutrophil chemotaxis even in the absence of complement activation. The peptide fMet-Leu-Phe reacts with a specific receptor on neutrophils and stimulates chemotaxis towards the source of the peptide. This peptide is considered a specific recognition signal for bacteria, as bacteria use formyl (-CHO) methionine as the first amino acid on their proteins. (In contrast, mammals use ordinary methionine for their first amino acid into proteins). Thus cleavage of bacterial proteins will generate fMet peptides and fMet peptides will be easily distinguished as foreign.
|
|
|
Q: Describe glomerulonephritis and the role of neutrophils in it?
|
-Glomerulonephritis from Ig and complement deposition on the kidney. The deposition stimulates the neutrophils to try to kill the tissue that was pathologically coated with the opsonins. This is an example of ''frustrated phagocytosis". It occurs with many chronic viral infections such as hepatitis B and diseases like systemic lupus erythmatosus
|
|
|
Q: What role do neutrophils have on acute lung diseases (such as adult respiratory distress syndrome)?
|
-Activation by complement in the lung may bring in neutrophils which then release arachidonic acid metabolites, proteases, and oxygen metabolites. Alveolar endothelium is damaged, possibly by the proteases elastase and collagenase, and blood plasma then exudes into lungs.
|
|
|
Q: What role do neutrophils have on chronic lung diseases (such as emphysema)?
|
-Neutrophil elastase may destroy alveolar elastin fibers. The best evidence that neutrophil elastase is involved in emphysema comes from the patients who have mutant alpha1 protease inhibitor (alpha1-PI). alpha1-PI is one of the blood serpins
|
|
|
Q: What are mononuclear cells?
|
-The term "mononuclear cell" is really a misnomer because most cells in the body have one nucleus. Used as an adjective for blood cells, "mononuclear" implies cells with rounded nuclei as opposed to lobed nuclei. Thus peripheral blood mononuclear cells (commonly abbreviated PBMs) include lymphocytes and monocytes and exclude the polymorphonuclear leukocytes which are the neutrophils, eosinophils, and basophils. Mature red blood cells in circulation lack nuclei and are also excluded from the PBMs.
|
|
|
Q: How do monocytes differ from lymphocytes?
|
-Monocytes differ from lymphocytes in their morphology and their lineage. Monocytes have lack receptors for specific antigens and have characteristic kidney shaped nuclei, and small granules. Monocytes belong to the myeloid lineage from bone marrow stem cells, a lineage which they share with the neutrophils.
|
|
|
Q: What percent of peripheral blood mononuclear cells are monocytes?
|
-Monocytes constitute 8-20% of peripheral blood mononuclear cells.
|
|
|
Q: At what level of differentiation are monocytes and macrophages?
|
-Both monocytes and macrophages are final or "end" cells of differentiation. These cells are unable to undergo any more cell division. A circulating monocyte is a nonadherent, small cell that can become an adherent macrophage with fibroblast-like extensive cell processes.
|
|
|
Q: At what locations are mobile monocytes located in the peripheral blood?
|
-Histiocytes wandering through tissues
-Langerhans cells in skin -Splenic and lymph node macrophages including dendritic cells which have long processes -alveolar monocytes -gianct cells-fused multinucleated cells in disease |
|
|
Q: What are examples of fixed macrophages?
|
-Kupffer cells of liver which constitute 15% of the liver mass,
-Osteoclasts which have 1-100 nuclei and function in bone resorption. |
|
|
Q: How do monocytes and neutrophils differ?
|
-Monocytes and neutrophils differ in morphology, longevity and function. Morphologically, circulating monocytes and neutrophils differ in the shape of their nuclei (kidney shaped vs. lobed), their cell size (small vs. large), and the granularity of their cytoplasm (less granular monocytes vs. neutrophils). Monocytes have long half lives, of days or weeks or longer, in contrast to neutrophils. They differ in their time of appearance at inflammatory sites and role. Neutrophils come in first, in large numbers, to engulf and kill infectious microbes. Macrophages enter secondarily to present antigens and facilitate other functions.
|
|
|
Q: What happens when monocytes become macrophages?
|
-When monocytes become macrophages (or "big-eaters") they become capable of phagocytosis and can ingest large particles as do neutrophils, using identical cell surface receptors (CR3, Fe-gamma receptors). Like neutrophils, macrophages ingest and digest particles using their phagolysosomes.
|
|
|
Q: What are the functions of monocytes and macrophages?
|
-Previous functions of macrophages included antigen presentation and killing of their own mtracellqlar bacterial infections. Remember that the CD4+ delayed type hypersensitivity T cells could secrete gamma interferon to induce the macrophages to become activated and able to kill intracellular bacterial. The bacteria include Mycobacterium tuberculae that causes TB and Mycobacterium leprae that causes leprosy.
|
|
|
Q: What are two new functions of monocytes and macropahges?
|
-Phagocytosis of the Apoptotic Bodies of Cells after their Death by Apoptosis. In living cells, the lipid phosphatidylserine is located on the inside of the plasma membrane. During apoptosis, phosphatidyl serine is flipped to the outside of the plasma membrane of the dying cell. When an apoptotic cell dies, it fragments into several apoptotic bodies that are still bounded by membranes (with phosphatidyl serine on the outside). Macrophages recognize the externalized phosphatidylserine, engulf the apoptotic cell fragments, and digest them down to simple biochemical compounds.
-Macrophages late at the site of wounds make fibroblast growth factor to promote healing (and scar formation). Fibroblast growth factor recruits fibroblasts to the site, supports their growth, and supports angiogenesis. Macrophages are very sophisticated cells and change their functions over time. |
|
|
Q: Give a summary of neutrophils and macrophages.
|
-The crucial role of macrophages is to be long term participants in inflammation Macrophage ingestion of bacteria leads to much more than simple killing of the microbes.
-Glucocorticoid drugs, like dexamethasone and prednisone, alter the expression of ~100 genes (including IL-l and TNF-alpha) that are regulated by glucocorticoid response elements (GREs). GREs are specific regions of DNA that are upstream of steroid-responsive genes. Depression of monocyte function is one of many contraindications for chronic use of glucocorticoids. |
