BIOE 301 Lecture Eight Amit Mistry Feb 6, 2007

BIOE 301 – Lecture 8 WARM-UP Observation: Global average near-surface atmospheric temperature rose 1.1 ± 0.4 °Fahrenheit in the 20th century. What is the scientific approach to this? What is the engineering approach to it?

Review of Lecture 7 Science “Science is the human activity of seeking natural explanations for what we observe in the world around us.” Five steps of the scientific method Engineering Systematic design, production and operation of technical systems to meet practical human needs under specified constraints Six steps of the engineering design method

Q3: How can technology solve health care problems? CS1: Prevention of infectious disease

Roadmap of CS 1 Science Organisms that cause infectious disease Immunity Engineering How to make a vaccine Vaccines: From idea to product Societal Impact Health and economics Ethics of clinical trials Developed world/Developing world

Connections – First day of class What caused the first bone marrow transplants to be rejected by recipients?

Bone Marrow - Pluripotent Stem Cells Hematopoietic stem cells differentiate into: White blood cells Red blood cells Platelets Mesenchymal stem cells differentiate into: Bone, cartilage, muscle

White Blood Cells NeutrophilLymphocyteMacrophage “The Defense” “The Good Guys”

Pathogens How They Cause Disease “The Offense” “The Bad Guys”

Types of Pathogens Bacteria Cells with membrane and cell wall (usually) Can survive outside host; reproduce without host Can be killed or inhibited by antibiotics Viruses Nucleic acid core with protein envelope Use host intracellular machinery to reproduce Cannot be killed with antibiotics >50 different viruses that can infect humans

Question: Based on your understanding of the characteristics of bacteria, viruses, and blood cells, identify which item best represents each and be able to explain why you chose each. Bacterium Virus Blood cell

Pathogens Human hair – 100,000,000 nm Red blood cell – 7,000 nm E. coli bacteria – 800 nm Virus – 100 nm

Bacteria

How do Bacteria Cause Disease? Invade host Reproduce Produce toxins  disturb cell function Examples Escherichia Coli Bacillus Anthracis Microbacterium tuberculosis Streptococcus pneumoniae

Virus

How do Viruses Cause Disease? Virus invades host cell Binds to cell membrane receptors Endocytosis brings virus into cell Virus takes over cell Use viral nucleic acid and host cell resources to make new viral nucleic acid and proteins More virus is released from host cell Virus causes host cell to lyse OR Viral particles bud from host cell surface

Virus examples: Influenza, HIV, West Nile, Hepatitis Human Papillomavirus, Viriola Major

Using Viruses for Good, not Evil Gene Therapy: infect cells with beneficial DNA Diabetes SCID Cancer Sickle cell anemia MS Cystic fibrosis

Pathophysiology of HIV/AIDS

The Immune System How Are We Protected Against Pathogens?

Types of Immunity Three layers of immunity: Physical Barriers Innate Immune System All animals possess Adaptive Immune System Vertebrates possess Keep pathogens out Kill them if they get in

Types of Immunity - Defense Line of scrimmage Physical Barriers = Defensive Line Innate = Secondary Defense Adaptive = Coach

Types of Immunity Physical Barriers Skin (2 square meters) Mucous Membranes (400 square meters) Innate Immune System Produces general inflammatory response when pathogens penetrate physical barriers Adaptive Immune System Can adapt to defend against any invader Important when innate immune system cannot defend against attack Provides immune system with “memory”

Physical Barriers

What happens when you get a splinter?

Pathogens gets past physical barrier 1. Macrophages eat bacteria on splinter Phagocytosis 2. Activated macrophages produce chemicals which: Increase local blood flow Increase permeability of blood vessels Recruit other phagocytes to site Redness Heat Swelling Pus

What happens when you get a splinter? Phagocytosis 119/9/1903/DC1

Innate Immune System Primarily effective against pathogens outside of cells Two main weapons: 1) Professional phagocytes Cells that eat stuff 2) The complement system Proteins that tag stuff for destruction

Components of Innate Immune System 1) Macrophages: Sentinels that patrol periphery If they find an invader, they become “activated” If activated, they: Send signals to recruit other immune system cells (Neutrophils) Become vicious killers Present antigen to adaptive immune system (more on this later)

Components of Innate Immune System 2) Complement proteins Present in tissues & blood Attach to surfaces of bacteria and viruses Target them for destruction by phagocytes Form Membrane Attack Complexes Recruit other immune cells from blood

Adaptive Immune System Antibody-mediated: Fight pathogens outside of cells Cell-mediated: Fight pathogens inside of cells

What is an antibody? Bridge between: Pathogen Tool to kill it Antibodies have two important regions: Fab region: Binds antigen Binds surface of virus-infected cell Fc region: Binds macrophages and neutrophils, induces phagocytosis Binds natural killer cell, induces killing

Question: Which components of your kit are most like antibodies? Arrange the components of the kit to demonstrate how these antibodies “bridge” a pathogen and the tool to kill it?

Antibodies How are antibodies made? B cells Lymphocytes that make antibodies Have B cell receptors on surface 100 million different types of B cells, each with different surface receptors B cell receptors are so diverse they can recognize every organic molecule When a B cell binds antigen: Proliferates - In one week, clone of 20,000 identical B cells Secretes antibody

Adaptive Immune System How do we kill virus once inside the cell? Antibodies cannot get to it Need T cells T Cells Recognize protein antigens When bind antigen, undergo clonal selection Three types of T Cells: Killer T Cells (Cytotoxic T Lymphocytes – CTLs) Helper T Cells (targeted by HIV) Regulatory T Cells

How do T Cells ID Virus Infected Cells? Antigen Presentation All cells have MHC molecules on surface When virus invades cell, fragments of viral protein are loaded onto MHC proteins T Cells inspect MHC proteins and use this as a signal to identify infected cells

Question: Using the components of the kit, demonstrate the two steps required for viral antigens to be presented on the MHC complexes on the surface of the blood cell.

Question: Demonstrate how the T cell can identify a virus infected cell. Why is this component of the adaptive immune system a significant advance over the innate immune system?

Immunologic Memory First time adaptive immune system is activated by an antigen: Build up a clone of B cells and T cells Takes about a week After infection is over, most die off Some remain – memory cells Second time adaptive immune system is activated by that antigen: Memory cells are easier to activate Response is much faster – no symptoms

Putting it all together

Virus invadesAntibodies bindPrevent virus function Signal phagocytosis Present antigen Activates Killer T cells Activates B cells Make more antibodies Infects cells Antigen presentation Kill infected cells!

Virus invadesAntibodies bindPrevent virus function Signal phagocytosis Present antigen Activates Killer T cells Activates B cells Make more antibodies Infects cells Antigen presentation Kill infected cells! Cell-mediated Antibody-mediated

Summary of Lecture 8 Pathogens: Bacteria and Virus Levels of Immunity: Barriers  First line of defense Innate  Inflammation Phagocytes Complement Adaptive  Immunologic memory Cell mediated immunity  Pathogens within cells Antibody mediated immunity Diversity to recognize 100 million antigens

Turn in HW 4 today Next Time Project Task 2 due on 2/8/07 Influenza virus Vaccines The most cost-effective medical intervention known to prevent death or disease

For more info: National Bone Marrow Program Baylor Center for Cell and Gene Therapy Immunobiology – BIOS Dr. Novotny