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Defense against Infectious Disease
Crash Course videohttps://www.youtube.com/watch?v=CeVtPDjJBPU
IB Assessment Statement
• Define pathogen. Pathogen: an organism or virus that causes a disease.
Key Concepts
• Pathogen – an organism or virus that causes diseases– Bacteria (strep throat, staph infections, pneumonia)– Protists (malaria, amoebic dysentery)– Virus (common cold, flu, herpes, AIDS)– Fungus (athletes foot, yeast infections)– Flat worms, round worms
• Host – the organism that is being attacked or invade by pathogen.
Prokaryotes
• Assessment Statement• 2.2.1 Draw, label and snnotate a diagram of
the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote.
• The diagram should show the cell wall, plasma membrane, cytoplasm, pili, flagella, ribosomes and nucleoid (region containing naked DNA).
Annotate: Label & Function
IB Learning Objective
• Explain why antibiotics are effective against bacteria but not against viruses.
What do antibiotics do?
• Antibiotics are effective against bacteria but not against viruses.– Antibiotics block specific metabolic pathways
found in bacteria. – Viruses reproduce using the host cell’s metabolic
pathways, which are NOT affected by antibiotics.
Bacteria vs. VirusBacteria• Are considered living organisms• Unicellular• Reproduce on their own• Need energy, and a metabolism• Have cell walls
Virus• Are NOT considered living• NOT made of cells• CanNOT reproduce on their own• Do NOT need energy , and so no
metabolism.• Do NOT have a CELL WALL
Antiobiotics
• Antibiotics are naturally occurring substances obtained from fungus or bacteria.
• There are over 4000 different antibiotics , but only 50 have proved to be safe.
How exactly do antibiotics work?
• Antibiotics are extremely effective at disrupting bacterial metabolism.
• Specifically antibiotics inhibit the formation of a new cell wall during cell division.
Learning Objective
• Outline the role of skin and mucous membranes in defence against pathogens.
Immunity
Immunity is a resistance to an infection.
There are two types of immunities:1. Innate Immunity2. Acquired Immunity
External Defenses –First Line of Defence
• Skin and mucous membranes are physical barriers to entry of microorganisms and viruses
• Mucous membrane cells produce mucus, a viscous fluid that traps microbes and other particles
• In the trachea, ciliated epithelial cells sweep mucus and any entrapped microbes upward, preventing microbes from entering the lungs
LE 43-310 µm
• Secretions of the skin and mucous membranes provide an environment hostile to microbes
– Secretions give the skin a pH between 3 and 5, acidic enough to prevent colonization of many microbes
– Skin secretions include proteins such as lysozyme, which digests bacterial cell walls
• Stomach has a pH of 3 which can kill most microbes.
IB LEARNING OBJECTIVE
• Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues.
Internal Immunity --Key Concepts
• Phagocytes – leukocytes (white blood cells) that circulate the blood identify pathogens and ingest (eat) them.
Innate Internal Immunity
• Macrophages, a type of phagocyte, migrate through the body and are found in organs of the lymphatic system– The lymphatic system defends against pathogens
Parts of the Lymphatic System
Adenoid
Tonsil
Lymphnodes
Peyer’s patches(small intestine)
Spleen
Appendix
Lymphaticvessels Lymph
nodeMasses oflymphocytes andmacrophages
Lymphaticvessel
Bloodcapillary
Tissuecells
Lymphaticcapillary
Interstitialfluid
Innate Internal Immunity
Phagocytic Cells•Phagocytes attach to prey via surface receptors and engulf them, forming a vacuole that fuses with a lysosome
LE 43-4
PseudopodiaMicrobes
MACROPHAGE
Lysosomecontainingenzymes
Vacuole
http://www.youtube.com/watch?v=7VQU28itVVw
http://www.youtube.com/watch?v=aWItglvTiLc&NR=1
Phagocytosis Tutorial
• http://www.microbelibrary.org/images/tterry/anim/phago053.html
Innate Internal Immunity
Antimicrobial Proteins•Proteins function in innate defense by attacking microbes directly or impeding their reproduction
•About 30 proteins make up the complement system, which causes lysis of invading cells and helps trigger inflammation
•Interferons provide innate defense against viruses and help activate macrophages
Innate Internal Immunity
Inflammatory Response•In local inflammation, histamine and other chemicals released from injured cells promote changes in blood vessels
•These changes allow more fluid, phagocytes, and antimicrobial proteins to enter tissues
LE 43-6
Pathogen Pin
Chemical signals
CapillaryPhagocytic cells
Macrophage
Red blood cell
Bloodclottingelements
Blood clot
Phagocytosis
Acquired Immunity
• Immunity is based on the body to recognize ‘self’ and to distinguish ‘self’ from ‘non-self’
• Antigen- Any ‘non-self’, foreign substance in the body. – Anything that causes a disease is an antigen
Lymphocytes
• Lymphocytes: Are specialized cells with the ability to recognize antigens and take steps to remove them from the body.– If a lymphocyte detects an antigen in the body it
will divide and produce clones of itself rapidly.– Some cloned lymphocytes will secrete proteins
called Antibodies.
IB LEARNING OBJECTIVE
• Distinguish between antigens and antibodies.
6.3.5 Distinguish between antigens and antibodies.(2)
• Antigen is often used to describe something that has infected the body. However it is more accurate to describe them as follows:
• An antigen is a large molecule (protein, glycoprotein, lipoprotein or polysaccharide) on the outer surface of a cell.
• All living cells have these antigens as part of their cell membrane or cell wall. • The capsid proteins of viruses and even individual protein molecules can also be classed as
antigens. • Their purpose is for cell communication, and cells from different individuals have different
antigens, while all the cells of the same individual have the same antigens. • Antigens are genetically controlled, so close relative have more similar antigens than
unrelated individuals. • Blood groups are an example of antigens on red blood cells, but all cells have them. • The link with infection is that when a pathogen or toxin enters the body it this that the
immune system reacts against.
6.3.5 Distinguish between antigens and antibodies.(2)
• Antibodies are proteins secreted from lymphocytes that destroy pathogen and antigen infections
• B-cells make antibodies. • An antibody (also called an immunoglobulin) is a protein molecule that can bind specifically
to an antigen. • Antibodies all have a similar structure composed of 4 polypeptide chains (2 heavy chains and
2 light chains) joined together by strong disulphide bonds to form a Y-shaped structure. • The stem of the Y is called the constant region because in all immunoglobulin's it has the
same amino acid sequence, and therefore same structure. • The ends of the arms of the Y are called the variable regions of the molecule because
different immunoglobulin molecules have different amino acid structure and therefore different structures.
• These variable regions are where the antigens bind to form a highly specific antigen-antibody complex, much like an enzyme-substrate complex.
6.3.5 Distinguish between antigens and antibodies.(2)
• Each B-cell has around 10 5 membrane-bound antibody molecules on its surface and can also secrete soluble antibodies into its surroundings.
• Every human has around 108 different types of B cell, each making antibodies with slightly different variable regions.
• Between them, these antibodies can therefore bind specifically to 108 different antigens, so there will be an antibody to match almost every conceivable antigen that might enter the body.
ANTIBODIES
• Antibody is a specialized protein that binds with antigens.– It is Y-shaped– it contains an amino acid sequence that binds
with the antigen, called an antigen binding site– There are millions of different types of antibodies
• Antibody Structure
Antigen-binding sites
Antigen Antibody
IB LEARNING OBJECTIVE
• Explain antibody production
Lymphocytes & Antibody
• There are millions of difference lymphocyte cells.
• Each lymphocyte recognizes one specific antigen
• Each lymphocyte secrete a specific antibody to combat a specific antigen.
• Every antigen that our body has been exposed to has a unique lymphocyte.
Memory Cells
• Once an antigen is destroyed the corresponding lymphocyte cell gets destroyed too.
• But ‘knowledge’ of this antigen is stored in memory cells that are stored in our lymph nodes.
Memory Cells
• If we are reinvaded by the same antigen our body can responding rapidly, using those memory cells.
• If we are re-invaded by the same antigen we can easily destroy that antigen, we say we have an immunity to that antigen.
Memory cell
Antigen Antigen binding to lymphocyte
Lymphocyte
Plasma cell
Production of many more cells and antibodies
Second exposure to same antigen
Production of memory cells
Antigen Antigen binding to lymphocyte
Lymphocyte
Plasma cell
Memory B cell
Lymphocytes grow and divide rapidly
Antigen Antigen binding to lymphocyte
Lymphocyte
Plasma cell
Some lymphocyte cells develop into plasma cells. Plasma cells produce antibodies that are released into the bloodstream.
Antigen Antigen binding to lymphocyte
Lymphocyte cell
Memory cell
Some lymphocyte cells develop into memory cells.
Production of many more cells and
antibodies
Second exposure to same antigen
Production of memory cells
Antibody Production• (a) There are many different lymphocytes.• (b) The antigen infects and is presented to
the lymphocytes• (c) The lymphocyte with a surface epitope
complementary to the antigen is selected.• (d) The Lymphocyte clones to produce
many plasma cells. This occurs in the lymph nodes.
• (e) The clone of plasma cells• (f) The gene for the antibody is expressed
and secreted into the plasma and tissue fluid.
• (g) The antibody circulated in body fluids destroying the infectious antigen
How do Antibodies KILL?
• Antibodies destroy antigens in different ways:– Antigens that are toxins can be inactivated by a
reaction with the antibodies– Antibodies can attach to antigens and make sure
that a phagocytic cell will recognize it. – Antibodies can kill bacteria by destroying their
cell walls….and cause the bacteria to lysis.
Practice Question
Which of the following best describes antibodies?
• A. Made by phagocytes and specific to one antigen
• B. Made by lymphocytes and specific to one antigen
• C. Made by leucocytes and non-specific• D. Made by phagocytes and non-specific
Immune Response Animaton…• http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/animation__t
he_immune_response.html• http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/
animation__ige_mediated__type_1__hypersensitivity__quiz_1_.html• http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/
animation__antigenic_determinants__epitopes_.html• http://www.bio.davidson.edu/courses/immunology/Flash/Bcellmat.html
Types of Immunity
Innate Immunity• Rapid responses to a broad
range of microbes:• Two Types:
1. Internal• Phagocytic cells• Antimicrobial proteins• Inflammatory response
2. External• Skin• Mucous membranes• secretions
Acquired Immunity• Slower responses to specific
microbes– Humoral response
(antibodies)– Cell mediated responses
(cytotoxic lymphocytes).
Learning Objective
• Outline the effects of HIV on the immune system.
Below is some great information about HIV Virus:
http://www.avert.org/hiv-structure-and-life-cycle.htm
Human Immunodefiency Virus (HIV)
• HIV– First Identify in 1983– HIV is a tiny Virus that
consists of:• 2 single strands of RNA• Few enzymes• all enclosed in a
protein coat.
Human Immunodefiency Virus (HIV)
HIV Enzymes– Reverse Transcriptase – Synthesizes DNA from RNA– protease - When viral RNA is translated into a polypeptide sequence,
that sequence is assembled in a long chain that includes several individual proteins (reverse transcriptase, protease, integrase). Before these enzymes become functional, they must be cut from the longer polypeptide chain. Viral protease cuts the long chain into its individual enzyme components which then facilitate the production of new viruses.
– Integrase – integrate viral DNA into host DNA
HIV is a retrovirus
• A retrovirus because it contains RNA NOT DNA.
• Retrovirus mutate (so EVOLVE) rapidly, this is the reason it is so difficult to find a cure.
• The flu is a retrovirus…this is why you need a new vaccine every year.
VIRUS are not considered Alive
• Virus are not considered alive b/c– The must use a HOST CELL’s DNA & enzymes to
replicate and reproduce– The do not need energy– They are not made of cells.
HIV uses Lymphocytes.
• HIV uses Lymphocytes to reproduce.– The lymphocyte attacked by HIV is called T-cells or
T lymphocytes.– The virus eventually destroys the T-cells that it is
using to replicate itself.– Thus a person with HIV has a lower than normal
amount of T-cells.– T-cells are immune cells that help us fight disease
thus when are T-cells are low we can get sick frequently.
Importance of Helper T-cells in the immune system
• http://highered.mheducation.com/sites/0072507470/student_view0/chapter22/animation__t-cell_dependent_antigens__quiz_1_.html
HIV INFECTION OF A T-CELL
1. Virus enters the blood.2. Virus bonds and fuses with T-cell3. Virus enters the cytoplasm of host cell via
endocytosis4. In the cytoplasm of the T-cell, Viral RNA is
changed to Viral DNA using the enzyme reverse transcriptase
5. New viral DNA moves into the nucleus of t-cell
HIV INFECTION OF A T-CELL
6. Once inside the T-cell’s Nucleus viral DNA is integrate into the T-cell’s DNA.
7. Virus DNA can remain in T-cell’s DNA for years. This would be harmless to the T-cell, and we call this latent.
HIV INFECTION OF A T-CELL
8. Onset of AIDS occurs when the viral DNA becomes active.
9. The virus reproduces rapidly inside the T-cell then buds off (exocytosis) and infects more T-cells
10.When enough T-cells are damaged a person has a severely compromised immune system.
HIV INFECTION of A T-Cell
6.3.7 Outline the effects of HIV on the immune system.(2)
• HIV is a virus that selectively infects Lymphocytes
• (a) Different lymphocytes• (b) HIV virus• (c) Infection as the virus attaches then enters
the host lymphocyte.• (d) The infected lymphocyte is 'disabled' by the
virus• (e) When an antigen infection is presented the
lymphocyte cannot produce antibodies.• (f) The antigen is not challenged by the
immune system and is able to freely proliferate
• The consequence is that the infected individual will have no immune and develop that disease.
• Therefore an individual who is HIV +ve (infected ) will eventually develop a disease which will go unchecked. The consequence is that that disease will severely damage the infected person and will eventually bring about their death
HIV Animations
• http://www.sumanasinc.com/webcontent/animations/content/lifecyclehiv.html– http://www.aegis.com/topics/virus/– http://highered.mcgraw-hill.com/sites/
0072507470/student_view0/chapter22/animation__hiv_replication.html
– http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/animation__how_the_hiv_infection_cycle_works.html
IB Assessment Statement
• Discuss the cause, transmission and social implications of AIDS.
6.3.8 Discuss the cause, transmission and social implications of AIDS.(3)
•Social Implications: Aids takes an economic and social toll by Belinda Beresford Africa Recovery June 2001•AIDS: Acquired Immuno deficiency syndrome.•Acquired relates the infectious nature of AIDS through the transmission of the HIV virus.•Immuno deficient relates to the way diseases cannot be resisted. •Syndrome relates to the variation in the way the disease manifest itself. People who develop AIDS can be a affected by quite different set of diseases. •Cause: is the HIV retro-virus that selectively infects cells of the immune system effectively disabling primary and secondary response to infection.•Transmission: Through contact with the body fluids of an infected person. In particular the fluids are blood and semen, vaginal mucus. There is a very low risk ( almost zero) associated with salivary mucus.
TED TALKS ON AIDS•http://www.ted.com/talks/hans_rosling_the_truth_about_hiv
