Pathogens Any biological agent that can cause a disease Examples: bacteria, viruses, fungi, protists, worms Bacteriophage Vibriocholerae Ebola virus Plasmodium falciparum Rust caused by a fungus
Pathogens Immune system cells patrol the body (blood and tissues) Immune system detects foreign particles + cells Additional responses: proteins blocking viruses from entering cells or punching holes in bacterial cell wall / membranes Immune system must be able to distinguish non-self from self Macrophage engulfing a yeast cell
How do antibiotics work? Bacteria have a metabolism + cell wall (prokaryotic cell) Antibiotics block metabolic pathways found in bacteria Eukaryotic cells are unaffected Viruses are not cells Viruses = protein capsid + nucleic acid -> they don’t have the machinery necessary to reproduce on their own
How do viruses work?
First line of defense Goal = to stop pathogens from entering the body SKIN layers:
Epidermis: dead layer superficial / contains keratin = impermeable
Respiratory tract produces chemical secretions (mucus) that trap or kill microbes
Lysozymes present in mucus, tears, saliva, breast milk = anti-bacterial
Cilia sweep the mucus back to the throat = germs go to stomach and acid environment destroys them
Second Line of Defense (Once pathogens get within the body...) FIRST: non-specific response Phagocytosis: ingestion + digestion of bacteria and other foreign substances Phagocytic leucocytes (aka macrophages): large white blood cells that engulf pathogens http://www.youtube.com/watch?v=fpOxgAU5fFQ&NR=1
Local inflammatory response Activated macrophages and mast cells at the injury site release chemical signals (like histamines) that act on nearby capillaries. Capillaries widen and become more permeable allowing fluid containing antimicrobial peptides to enter the tissue. Signals also attract additional phagocytic cells. Phagocytic cells digest pathogens and cell debris at the site, and the tissue heals.
Antigens Molecule recognized by the immune system = triggers a response (ex: production of antibodies) All cells have antigens – part of membrane/cell wall (protein, glycoprotein, lipoprotein or polysaccharide) Purpose = cell communication Cells from different individuals have different antigens Antigens are genetically controlled, so close relative have more similar antigens than unrelated individuals. Example: blood antigens
Antibodies (or Ig = immunoglobulin) Proteins made of 4 polypeptide chains Produced by lymphocytes B (plasma cells) Bind to specific antigens in areas called epitopes Antibodies help identify / neutralize pathogens Part of acquired immunity (vertebrates are unique – most animals have only innate immunity)
Antibody Production Specific immune response Pathogen enters the body Macrophage engulfs pathogen Pieces of pathogen become part of macrophage’s membrane Antigen presentation = lymphocytes T recognize pieces = become activated T cells activate specific B cells – they divide (cloning) and form: Plasma cells = secrete antibodies that bind to antigens Memory cells = stay in circulation http://www.youtube.com/watch?v=lrYlZJiuf18 B cells = mature in the bone marrow T cells = mature in the thymus
The Lymphatic System
HIV Isolated in 1983 by Robert Gallo of the United States and French scientist Luc Montagnier. AIDS = AcquiredImmunodeficiency Syndrome Transmission: body fluids – mostly blood, semen and vaginal fluid Atypical virus = retrovirus (RNA) Enzyme known as reverse transcriptase, allows HIV to produce DNA from RNA (whereas most cells carry out the opposite process, transcribing the genetic material of DNA into RNA) The activity of the enzyme enables the genetic information of HIV to become integrated permanently into the genome (chromosomes) of a host cell.
HIV infection HIV infects helper T cells T cells = activate and direct other leukocytes HIV attaches to CD4 receptors and injects its content inside the cell T cell is disabled RNA is reverse-transcribed, producing DNA which integrates to the cell’s genome Cell starts producing new viral particles Immune response is compromised High mutation rate because reverse transcription does not allow for correction of errors in nucleotide incorporation = great antigenic variation Latency period = inactive DNA Decline of T cells = HIV eventually causes AIDS A CD4 count of less than approximately 200 cells per microliter of blood may be accompanied by a variety of opportunistic infections and is considered the final stage of infection. The persistent barrage of such infections is what typically leads to the death of AIDS patients.
Issues involving HIV Difficult to develop medication = high mutation rate HIV associated with drug use and sexual activity = hard to allocate research money in the past Blood for transfusions was not tested in the past AIDS was labeled as a disease affecting homosexuals and drug abusers = discrimination HIV positive individuals = problems with employment, insurance, education access, etc... Some countries = inadequate medical care