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Lecture 10

MCB 2000 Lecture 10: Exam 4 - Lecture Notes

32 Pages

Microbiology and Cell Science
Course Code
MCB 2000
Abdolkarim Asghari

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Exam Four Lecture one Drugs & Antibiotics Immunology and Defense Mechanisms How to Control the Microbes Around Us • We know that the body’s normal flora has some bacteria all around the body. They have a life with us that starts from the minute that we’re born and they remain with us even after we die. • Microbes are involved in antagonistic activity. They fight for the location, space, nutrients. That’s how we found out about antibiotics. Some bacteria and fungi produced natural antibiotics to fight off other microorganisms. That’s how Alexander Fleming discovered Penicillin. • Sterilization – killing all life forms + viruses o Some organisms are killed faster than the others. Some organisms have endospores. o Endospores are a dormant form of life for some organisms. o Boiling water by itself is not enough sometimes to kill all organisms • Disinfection – physical process or a chemical agent to destroy germs and pathogens o It all removes toxins o Harsh chemicals. Cannot be used on human body or on live objects. Usually used on inanimate objects. • Antiseptics – Similar to disinfection, but usually milder chemicals. They can be used on living tissues. • How to control microbial growth: physical or chemical way o Physical methods mean that you: ▪ heat microorganism (dry heat and moist heat.) ▪ For moist heat, the temperature goes to about 121 degrees Celsius. ▪ Dry heat requires a much higher temperature than moist heat. Moist heat penetrates much better. ▪ radiate microorganism with ionizing radiation (such as deep penetrating radiation like an x-ray or gamma ray) ▪ radiate microorganism with nonionizing radiation (does not penetrate much into the tissue) o Mechanical means that there’s actual filtration ▪ Bacteria are usually .5 micrometers – 2 micrometers. Viruses are less than .5 micrometers. ▪ A filter that traps bacteria would have a diameter about .45 micrometers o Chemical methods include chemicals in gas or liquid form ▪ We have disinfectants and antiseptics • Most resistant to least resistant: o Prions – infectious proteins. They caused diseases such as CJD or mad-cow disease. It’s a neurological disorder. The protein survives even if you have your meat well done sometimes. o Bacterial endospores – the most resistant living agent. They are dormant forms of life. Two groups or organisms produce endospores: bacillus and clostrydium. Bacillus causes diseases like Anthrax. Clostrydium causes diseases like Tetanus, Botulinum, Gangrene, CDAD. Killing endospores is very difficult, it takes more energy and a higher temperature. o Mycobacterium o Staphylococcus and Pseudomonas – Pseudomonas is an organism that causes opportunistic infection. It has porins (channels that are present in the outer membrane of gram -). o Protozoan cysts – cysts are the transmission form of protozoans. o Protozoan trophozoites o Most gram-negative bacteria o Fungi and fungal spores o Nonenveloped viruses o Most gram-positive bacteria o Enveloped viruses • Overall, protozoans are harder to kill than general bacteria, viruses, or fungi Actions of Various Physical and Chemical Agents upon the Cell • One of the best targets is the cell wall of bacteria. The cell wall is made up of peptidoglycan and that is unique to bacteria. This is a selective toxicity. • By selective toxicity, I mean you have to find some targets in the infectious agent that is absent in the human or animal. You want to kill the pathogen, not the host. Remember, not all bacteria have cell wall. Those that do not have cell wall will not be affected by chemicals that target the cell wall. • The cytoplasmic membrane (cell membrane) is usually not the best target. If the cell membrane is disrupted, the cell immediately dies. One issue: the cell membrane of a human is very similar to the cell membrane of other organisms. However, for fungi, it is one of the better targets. • Cellular synthesis (metabolism). Cells use pathways to make things or to break things down. If we identify some pathways that are unique to bacteria, we can target those pathways. Obviouslywe can’t target glycolysis because everyonedoesglycolysis. We also can’t target Krept cycle. There are some unique pathways that we can target though (discussed later on) • Proteinsynthesisisagoodtarget.Youcanuseproteinsynthesistoaffectthecells.Protein synthesis is done in the ribosome (the ribosome in Eukaryote is different from the one in Prokaryotes). • DNA and RNA synthesis is also a good target. Basically, you can target replication so the bacteria cannot replicate. You can target transcription so the bacteria cannot make RNA. You can target translation, meaning the bacteria cannot make protein. • Heat is the best and most effective mechanism for controlling growth. That is why we heat up things. o Inthelaboratory,wehave autoclave.Itisachamberwhereyouputyourmaterials in andthenyousetupatemperature.Itfillsupthe chamberwithsuper-hot steam and eventually fills it up and pressurizes it. You have pressurized steam. The temperature goes above boiling temperature. That kills everything. o Another form of heat is incineration. o Dry oven is a dry type of heat. You need a higher temperature for dry heat, higher than steam. If your autoclave is 121 degrees Celsius, you go up to 300 degrees Celsius in the dryoven.You also need longer timefor exposure. Dry heat does not penetrate like moisture. o Another form of heat is boiling (wet heat). You cannot boil water at higher than 100 degrees Celsius. Sometimes boiling for even 20 minutes does not kill everything, like endospores. o Temperature denatures/coagulates the bacteria’s protein. The cell dies because the protein is destroyed. o As the temperature rises, the cell starts slowing down. After some temperature, the protein damage is irreversible. • Radiation o The shorter the wave, the higher the energy and the more damaging. The longer the wavelength, the less energy. o UV rays, X rays, and gamma rays all damage DNA. o Above visible light does not damage (ex: infrared, micro-waves, radio waves) o The further you get from UV, the safer it gets in terms of radiation. o UV light damages the cell by forming thymine dimers. It fuses the 2 T’s together. They are no longer recognized as 2 separate T’s, they are now recognized as one odd, unrecognizable base pair. It causes mutations. o The damage of UV light is superficial. You can see is through skin damage. Sunbathing results in skin cancer, not internal cancer. o X rays and Gamma rays break chromosomes. The damage is irreversible. They are deep penetrating into the tissue. They also cause cancer. • Proteins are exposed to heat or to chemicals become denatured. Denatured means the protein loses its structure. It goes back to primary structure. It no longer functions and the cell dies. Chemicals in Commercial Antimicrobial Products • Lysol has a phenol-based compound. • Most products have alcohol in them • Some chemicals are not good for humans. The best way is to not let things get contaminated and keeping them clean to reduce the amount of chemical used regularly. Gram negatives: • More resistant to antibiotics because they have the outer membrane. • The outer membrane has its own porins, which don’t allow chemicals to filter in. • This extra layer also serves as a protective layer against chemicals. • Sometimes very hard to kill, not only by chemicals but by antibiotics. Antibiotics have to overcome outer membrane AND cell membrane to get inside. Characteristics of the Ideal Antimicrobial Drug • Selectively toxic to the microbe but nontoxic to host cells • Microbicidal (kills the microbe) rather than microbistatic (stops the growing) • Relatively, soluble; functions even when highly diluted in body fluids • Remains potent long enough to act and is not broken down or excreted prematurely. • Does not lead to the development of antimicrobial resistance • Complements or assists the activities of the host’s defenses • Remains active in tissues and body fluids • Readily delivered to the site of infection • Reasonably priced • Does not disrupt the host’s health by causing allergies or predisposing the host to other infections Terminology of Chemotherapy • Chemotherapeutic drug: any chemical used in the treatment, relief, or prophylaxis of a disease. This is a general term for medicine that you take. • Prophylaxis: use of a drug to prevent imminent infection of a person at risk. It does not allow the disease to start in the first place • Antimicrobial chemotherapy: the use of chemotherapeutic drugs to control infection • Antibiotics: chemicals against bacteria. • Semisynthetic drugs: something that was originally produced by microbes, but humans have modified it in a lab. (ex: Penicillin G is a naturally made antibiotic by a fungi) • Synthetic drugs: drugs produced entirely by chemical reactions. Totally man-made • Narrow-Spectrum (Limited-Spectrum): antimicrobials effective against a limited array of microbial types- for example, a drug effective mainly against gram positive bacteria • Broad-Spectrum (extended spectrum): a drug effective against both gram positive and gram negative bacteria. This spectrum also kills your normal flora. • Some bacteria and some fungi make antibiotics. It is to kill the competition. Lecture two • Antibiotics are chemicals that are produced naturally by fungi and bacteria. The purpose is tofight competition.Usuallyfound in soilbacteria where there aren’t enough nutrients for all microbes. • Some antibiotics kill, some antibiotics stop the growth. • Some antibiotics are broad spectrum; some antibiotics are narrow spectrum. • It makes sense to eat yogurt and probiotics to replenish your bacteria. If you take antibiotics for too long, you are reducing your normal flora. • Zone of inhibition is where there is no growth on the agar plate. Targets that Antibiotics Choose: • Cell wall: major, very significant target. Bacteria have cell wall. Humans cells do not have cell wall; neither do animal cells. • Bacterial cell was is made up of peptidoglycan. Peptidoglycan synthesis is a target of antibiotics. • Mycoplasma (causes pneumonia) & Chlamydia do not have a cell wall • Some bacteria has unusually cell way, like mycobacterium (causes TB). nd • Proteinsynthesisisthe2 mostimportanttarget.Translationistheproteinsynthesisand it occurs in the ribosome. Ribosome in bacteria is much smaller. • Cell membrane is a target that has more side effects than the others. The cell membrane of all cells are similar. It is good for fungi. They have a unique cell membrane that others do not have. They have Ergosterol in their membrane. Humans have cholesterol in their membrane. • DNA/RNA (Nucleic Acid synthesis) is a target • Metabolic activities. There are some drugs (antimetabolites). They are man-made compounds that targets unique metabolic pathways in bacteria. • Pholic acid is a supplement that we need to take. In our body, we make nucleic acid but wedon’tmakethepholicacid.BacteriaDOmaketheirownpholicacid,thereforeitpholic synthesis is a good target Specific Drugs and their Metabolic Targets • There are antibiotics such as Penicillin and Cephalosporin that target cell wall synthesis. • We have antibitotics such as Bacitracin. It does not affect the synthesis but it affects the transporting of cell wall to the outside. • We have antibiotics such as Streptomycin that affect protein synthesis. • The first antibiotic discovered was Penicillin by Alexander Fleming. • Tetracyclin is antibiotic that targets protein synthesis • Vancomycin targets cell wall synthesis. It is different from Penicillin. They target the cell wall at different places. Cephalosporin and Penicillin target the same thing, they’re basically the same thing. • When MRSA develops, it is resistant to Cephalosporin and Penicillin, so it is treated with Vancomycin. • Antimetabolides: sulfur drugs, sulfonamides, trimethoprine – both target folic acid synthesis at different places. They are man-made chemicals that target metabolic activities of bacteria. • DNA and RNA can be targets. o Protein synthesis – translation o DNAS synthesis – replication o RNA synthesis- transcription • Ciprofloxacin - Causes the bacteria to lose the control of the DNA. It affects the replication. • Rifampicin affects the RNA synthesis. • Erythromycin and Streptomycin affects protein synthesis (translation) • Vancomycin, Penicillin, Cephalosporin affects cell wall synthesis • When you hear that they spray fruit trees with antibiotics, its to promote growth. Antibiotics are being overused, we put a lot of pressure on them. It forces the bacteria to mutate and change eventually. • Polymixins are cell membrane drugs. Characteristics of Penicillin: • Cell wall synthesis drug • It has a beta-lactam ring. This ring is responsible for the action of Penicillin. Methicillin, Amoxicillin, and Cephalosporin all have this ring • Penicillin G was the original antibiotic that was produced by fungi • Every form of Penicillin has an original structure plus another group attached to it. • Once they discovered that some bacteria became resistant to Penicillin, they switched over to Methicillin • MRSA (Methicillin Resistant Staphylococcus Aureus) • Vancomycin also affects cell wall synthesis but it does not have the beta-lactam ring. It also works against MRSA • Fungi have a cell wall that is made of chitin. Penicillin, Methicillin, Vancomycin would not work against them because there’s no peptidoglycan. When you have fungal infection, you cannot give the person Penicillin. • Fungi has Ergosterol which is a target • There are two classes of antifungal drugs: o Polyenes: Amphotericin B o Azoles: Ketaconazole, fluconazole, miconazole, clotrimazole o They both work against Ergosterole structure and metabolism. Polyenes disrupt the function; Azole disrupt the synthesis. • We haveahardtimetreatingfungalinfectionsbecausetheyare Eukaryotes,theirprotein synthesis is very similar to humans, they don’t have a cell wall that could be targeted, their metabolic activities are similar to those of humans. Many times antifungal drugs have bad side effects. Most of the time you don’t take them internally, you take them on the outside (rubbing on your skin is an example) Actions of Antiviral Drugs • Viruses are obligate intracellular pathogens. • They have no membrane, no cell wall, no protein synthesis, no replication, no transcription. They really on all of these on host. • There are some viruses (unique) that bring their own enzymes for replication • If you prevent the virus from entering the cells, it doesn’t matter if the virus is inside your body. It cannot live without being inside a cell. The presence of the virus in the blood is not toxic. It is toxic when they destroy cells • Preventing entry is the key to fighting viral infection • Fuzeon prevents the entry of the HIV virus into the host cells. • There are drugs that inhibit the nucleic acid synthesis • Acyclovir (brand name: Zovirax) is a structural analog. They mimic the structures that prevent the virus from synthesizing their own DNA. Purine analog (means that it mimics A and G). Most effective against the Herpes virus. • Zidovudine (AZT) affects the synthesis of HIV virus. It is a structural analog. • Inhibition of viralassembly/release.The virusproduces a longpiece of proteinthat hasto be chopped into small pieces. It is use to assemble a new virus. To chop them you need the enzyme, Protease. These antiviral drugs inhibit protease from occurring (called Protease Inhibitors or P.I.’s) • AZT affects reverse transcriptase (RT) enzyme. AZT is an RT inhibitor. • To treat HIV, you get a combination of P.I. and R.T. • Drug resistance is a problem. In the case of Penicillin, in the case of MRSA, some bacteria found a way to break down the beta-lactam ring. Bacteria have an enzyme called beta- lactamases that break down the ring. They make the antibiotic ineffective. • Inactivating the drug, preventing entry of the drug into the cell by changing the target, pumpdrugoutofcellfastenoughthatitwillneveraccumulateinside–allwaystobecome resistant to drugs. • If you give them antimetabolides, they use an alternative pathway. Lecture three: • An idealantibioticgoesdirectlytothe sourceof infection,killsthe infection,anddoes not harm the host. Selective toxicity tells us where are the weakest spots of the microbe that we can attack. In bacteria, the cell wall is a good target because it is made up of peptidoglycan. • Protein synthesis is another target because the ribosome of Eukaryotes is different from the ribosome of Prokaryotes. • Metabolic activities (pathways to make things): we both do glycolysis, Krept cycle, electron transport system. • The chemicals that affect the microbe metabolism are called antimetabolides. • Folic acid is very effective, it is necessary to make DNA and RNA. However, the human body does not make folic acid. It is part of our diet, we get it from the outside. Bacteria actually can make their own folic acid. • Another target is DNA/RNA synthesis • When you have a drug that targets the cell membrane, it has some toxicity to it because the human cell membrane and bacteria cell membrane are very similar. • But, fungi have some differences from other Eukaryotes. It cannot have Penicillin, Erythromycin, Vancomycin used against it because it does not have a cell wall made of peptidoglycan. • The cell membrane of fungi has a compound in it called ergosterol. • Polyenes target the structure of ergosterol o Amphotericin B is an antifungal drug • Azole target the synthesis of ergosterol. Actions of Antiviral Drugs: • Viruses are obligate intracellular pathogens. They go inside human cells and they need to use human cells’ components to live – they use host enzymes for transcription, replication, translation, metabolism, etc. • One way to stop the virus from doing its job is to stop the penetration and entry of the host. This can happen by preventing the ‘uncoding’ process of the virus. • Inhibiting the replication of the virus is another good target. • HIV is an RNA virus. RNA must be converted to DNA and get into the host chromosome. o Stopping the Reverse Transcriptase (R.T.) enzymes inhibits the RNA from being converted into DNA. R.T. is a huge target o There’s a drug called R.T. Inhibitors which is specifically for this ^ o Amantadine, (“Tamiflu”, “Relenza”) are drugs that block the entry of the virus by interfering with the fusion of the virus with the cell membrane of the host. They also stop the release of the virus. This prevents the spread of the virus. • Acyclovir isa drugagainst theherpes virus.Thisdrugisa structural analog.It’sa drugthat looks like nucleotides but it doesn’t actually function properly like a nucleotide. • Ribavirin is an antiviral drug given for hemorrhagic fever and also against hepatitis infection. • The most famous R.T. inhibitor is AZT (Zidovudine). It’s a drug of choice against R.T. • Another drug against HIV is called Protease Inhibitors (P.I.) • P.I. is usually given in combination with R.T. Mechanisms of Drug Resistance: • You can modify the drug • Decrease the drugs from getting in • You can bypass your pathway, and go to a detour • The goal is to not let your drug affect your processes • When you take antibiotics, your immune system relies on the natural population of microorganisms in your body called normal flora. Normal flora is important for microbial antagonism. Your bacteria prevent other bacteria from establishing residence in your body. • Taking antibiotics for a long period of time, it decreases the normal flora population. • Thereissomefoodthatcomeswithbacteria,whichhelpyourepopulatethenormalflora. They’re called probiotics. Dairy products are good for that. • Chemotherapeutics refers to all the chemicals that you take to protect you from all kinds of diseases. • Antibiotics are chemicals are against bacteria • Antimicrobials are against all kinds of microbes that cause infections • MIC is Minimum Inhibitory Concentration. It’s the lowest amount of drugs that kills or stops microbes from growing. MIC is needed for drug companies to decide how much they want you to take in a dose of medicine. • If you get less than MIC, it doesn’t work. If you get more than MIC, it doesn’t work any better. The Immune System • Host defenses include Innate Immunity and Acquired Immunity o Innate in nonspecific. Nonspecific immune system means: it doesn’t care what type of virus or what type of bacteria; it provides protection regardless just not specifically. ▪ Components of non-specific immunity: • First line of defense: includes physical barriers like skin, mucous membrane. It is a surface protection composed of anatomical and physiological barriers. • The skin has low pH, sweat, high salt, lysozyme (enzyme that kills cell wall of bacteria), normal flora. These are anatomical defenses. • The stomach has acidity. You have bile salts that also kill bacteria • The kidney is sterile,but thebladdercontains some bacteria. When youurinate,yougetridofthebacteria.Holdingabladderforalong time allows the bacteria to ascend and go to the kidney, causing kidney infections. • Cilia refers to the short appendages that cover the trachea. They push the bacteria upward so they won’t fall down into the lung. • The mucous membrane is covered with mucous. Cilia may become inactivated by viral infection. It makes the person prone to secondary bacterial infection. • Secondlineofdefense:involvephagocytosis.Phagocytesphysically eat the infection and remove it from the body. Inflammation is characterized by swelling, redness, and pain. Fevers are when your temperature rises to 100 or 101. Fever slows down the viruses and activates your immune system. o Acquired is specific. Specific immune system cares about what type of infection it is. It reactsdifferentlyaccordingto the infection. It provides a specificmolecule to kill a specific infection. ▪ Components of specific immunity: • Third line of defense: includes specific host defenses that must be developed uniquely for each microbe through the action of specialized white blood cells. B cells and T cells are the most important “players” in the third line of defense. • All three lines of defenses work together. • The immune system is made of some cells, some organs, and some supporting molecules. • Allbloodcomponentscomefrombonemarrow-whitebloodcells,redbloodcells,platelets • The platelets are involved in blood clots. They prevent you from bleeding to death • Red blood cells carry oxygen around. • Red blood cells and platelets have no role in immunity; white blood cells are the ones that have a role in the immune system • White cells are located in the lymphatic system. • The heart pumps the blood; the blood goes all over the body. The oxygenated blood goes out; the deoxygenated blood comes back. When the blood reaches the end of the capillaries,the liquid comes off of the blood.All these liquidsare collectedbythe lymphatic tissue • The lymphatic system collects free liquid around the body • The lymphatic system is a network of vessels that run around the whole body. They collect liquid and the liquid, on the way back, is tested for any kind of presence of any microbes. • Stemcellsarelikearawmoleculethatyoucanshapetowhateveryouwant.Theycanmake red blood cells, white blood cells, platelets, anything. • White blood cells are called leukocytes • Red blood cells are called erythrocytes • A person with leukemia has white blood cell cancer. Doctors have to kill all of your white blood cells. They put you under radiation and get rid of all of your stem cells. Then they do the bone marrow transplant. They need to give you new stem cells. Lecture four • Immune system is a collection of some organs, such as thymus, bone marrow which are theprimaryorgans.Thenwe havethe spleen,lymphnodes,lymphatictissues, andtonsils which are the secondary organs. • All of the cells in the blood form elements. They all originate from the bonemarrow stem cells. • Thecellsthatturnintomyeloidsomeofthembecomeerythrocytes (redbloodcells).They have no role in the immune system. Platelets are blood clotting factors that also play no role in the immune system. • The immune system is divided into the innate vs. acquired. • Acquired is specific. B cells & T cells. o B cells are the only cells that produce antibodies. o T cells o B cells and T cells are also called lymphocytes. o Lymphocytes also include Natural Killer cells (aka NK cells). NK cells are part of the innate immunity as well, they work both ways. • Innate cells are nonspecific o Phagocytic cells – macrophages, monocytes, dendritic cells • Mast cells, Neutrophils, and Basophils are all involved in inflammatory response like allergies. • Phagocytic cells have small organelles inside called lysosomes. Inside the lysosome you find hydrolytic enzymes that kill bacteria. Lipase, protease, lysozyme, nuclease, are all hydrolytic enzymes that kill bacteria. There are also some harsh chemicals in it called oxidizing agents. These molecules can damage whatever microbes come in. o Phagocytic cells are attracted to the infection, bind to it, and they bring the bacteria in. When the bacteria come in its called Phagosome. Phagosome fuses with Lysosome. Thisfusion results in killing the bacteria. They expose the bacteria to chemicals to destroy it. o Dead cells can also remove viruses, fungi, bacteria, etc. Inflammatory Mediators and other Cytokines • Cytokines are proteins produced by the immune system cells. They use it for attacking bacteria; for communication; for activating immune cells. o Ex:ifTcellswanttotellBcellstomultiply,TcellsproduceCytokineswhichtriggers the other cells (B cells) to multiply. • Interferons: very important against viruses. • Tumor necrosis factor: important when it comes to cancer cells and cells that are in trouble. They destroy and kill other cells. • Inflammatory Mediators are chemicals that stimulate and cause inflammation. They are the result of degranulation of Mast cells, Eosinophils, and Basophils. These are three groups of white blood cells that have granules in them. Once they see the infection, they release the granules. Types of granules include: o Histamine o Serotonin o Bradykinin • Inflammation is the result of the body producing inflammatory compounds. It results in redness, swelling, heat, pain. • There’s acute inflammation which is quick to develop and heals quickly. It is beneficial. • Chronic inflammation is slow to develop, lasts long, and is damaging. It results in tissue repair and increases the blood flow in the area. • The reason they ask you to remove the infection in the body as much as possible is because of the chance of developing chronic inflammation. • Inflammation is nonspecific, part of the innate immunity. • The result of the inflammatory response is recruitment of phagocytic cells. By releasing these chemicals (inflammatory compounds), phagocytic cells are attracted to the area. They come and start working in the site of injury to fight the infection. • Neutrophils are the major phagocytic cells against bacteria. • Interferons are cytokines. They fight against viruses. o One cell is infected with the virus. o It produces interferons o The interferons go and alert the other cells o When the virus goes to attack other cells, they are protected because they produce interferon inside and the interferon will fight against the virus. o Interferons usually attack RNA of the virus to block replication. If the virus cannot replicate, there’s no damage. Innate Immunity • Complement proteins: a group of proteins floating in the blood on a regular basis. They are in inactive form. If the infection enters the body, they become activated by sensing the infection. When they are activated, it’s called complement fixation. o The activation happens when complement protein starts breaking down into pieces. For example, thebacteria comes in -> complement protein can bind to the surfaceofthebacteriaandbecomeactivated ->thefragmentsandpiecesproteins attachtothesurfaceofthebacteria->eventually,thisaccumulationoftheprotein results in the formation of Membrane Attack Complex (MAC). -> MAC pokes a hole onto the bacteria so there are multiple holes. -> the bacterial cell leaks, resulting in lysis (killed). o Complement fixation results in microbe lysis. o After the lysis: on the surface of the bacteria where MAC occurred, other complement molecules bind and coat the bacteria with these molecules. This phenomenon is called Opsonization. It helps with phagocytosis because it makes the bacteria attractive to phagocytic cells. • Complement proteins killthe infection; coat the infection with Opsonization; they attract phagocytic cells. What are antigens? • Antigens are molecules that illicit/triggers and activate the immune system responds to. • There are molecules on bacteria are recognized by phagocytic cells. The body recognizes bacteria with the molecules it has on its surface. • Example: Bacteria has pili, fimbriae, capsule, flagella, cell wall. All of these components can act as an antigen. • If you receive blood or organs from somebody else, those molecules could also work as antigens for your body. Your body reacts to organ transplants because every cell on that organ is not the same asthe cells on YOUR organ.Your body recognizes the molecules on the surface of the transplant organ as antigens. • Antigens must be big enough for the immune system to see them. • Proteins are the most antigenic. • Food particles, pollen, pet dandruff are all antigenic as well. How does your body recognize antigens? • Antigen must be recognized by B cells and T cells (acquired immunity). • B cells and T cells are supposed to see the infection. They are both part of the stem cells in bone marrow. B cells are activated and move on to other parts of the body. T cells before becoming full T cells, they have to mature in the Thymus. • One way of recognizing antigens is through the antigens being processed. Once the antigen is processed, it needs to presented to the B and T cells. o Antigen Processing/Presenting Cells (APC) are cells that see the antigen -> recognize the antigen -> process the antigen -> present the antigen to T helper cells. o Example of APC’s are B cells, macrophages, and dendritic cells. o T helper cells cannot see the infection directly. • When antigens are seen by B cells (which are activated cells), they become plasma cells and produce antibodies to fight the infection. • Some cells become activated, but they do not go all the way. These become Memory Cells. There are some T cells and B cells that become memory cells. o B cells do not become plasma cells, but they are partially activated. o Memorycells rememberinfectionforthefuture. If an infection comes backagain, they bind to it much faster than before. o Memory cells can last between months or years. Contrasting Properties of B cells and T cells • They are both lymphocytes B cells T cells Site of Maturation Bone marrow Thymus (originate from Bone marrow, but mature in the thymus) Specific surface markers Immunoglobulin (antibodies) T-cell receptor Several CD molecules Circulation in blood Low numbers High numbers Receptor for antigens B-cell receptor T-cell receptor (immunoglobulin) Seeing the antigen Directly Need APC Producing antibodies Only when they are plasma Do not produce them cells • B Cells – AMI • T Cells – CMI How Antigen is Presented to T Cells: • There are three APC’s – Dendritic cells, B cells, and macrophages. • Dendriticc
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