1. 6.3 Defense against infectious disease
IB Biology

2. Pathogens Any biological agent that can cause a disease
Examples: bacteria, viruses, fungi, protists, worms
Bacteriophage
Vibrio cholerae
Ebola virus
Plasmodium falciparum
Rust caused by a fungus

3. Pathogenic or Non-Pathogenic?

10. ANTIBIOTICS
Bacteriostatic
BACTERIOCIDAL
An antibiotic that stops bacteria from reproducing, while not harming them otherwise.
These are used in industries to prevent bacterial growth (ie on plastics)
An antibiotic that kills bacteria.
Any treatment or medicine to eliminate infections.

17. First line of defense Goal = to stop pathogens from entering the body
SKIN
layers:
Epidermis: dead layer superficial / contains keratin = impermeable
Dermis: thicker / contains dermal cells, glands, hairs, capillaries, sensory receptors

18. Additional barriers
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

19. Second Line of Defense (Once pathogens get within the body...)

20. Remember what the
2 types of white blood
cells do?

21. Types of Leukocytes
Phagocytes – a non-specific type of white blood cell that protects the body by ingesting harmful or dead material.
They help fight infection.
In large numbers, they look like pus.
Figure 10.4
Slide 10.10a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

22. Types of Leukocytes
Lymphocytes – a specific type of white blood cell that produces antibodies to fight specific antigens.
Figure 10.4
Slide 10.10a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

23. 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

25. 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.

26. Second Line of Defense (Once pathogens get within the body...)
SECOND: specific response
LYMPHOCYTES – white blood cells that recognize specific “foreigners”.
T Cells (made in the thymus)They seek and destroy; they produce a chemical that destroys intruders. Acquired immune system
B Cells (made in the bone marrow) They make antibodies for specific antigens. Acquired immune system
NK Cells (Natural Killer Cells) Part of the innate immune system that is already programed to eliminate viruses and cancerous cells.

28. The lymphatic system

31. 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

32. Antibodies (or Ig = immunoglobulin)
Proteins
Produced by lymphocytes
Bind to specific antigens
Antibodies help identify / neutralize pathogens
Part of acquired immunity (vertebrates are unique – most animals have only innate immunity)

33. The Lymphatic System Responsible for producing and circulating lymphocytes.

34. HIV What do you already know?

35. A virus: An ultramicroscopic (20 to 300 nm in diameter), metabolically inert, infectious agent that replicates only within the cells of living hosts.

37. HIV Isolated in 1983 HIV = Human Immunodeficiency Virus
AIDS = Acquired Immunodeficiency Syndrome
Transmission: body fluids – mostly blood, semen and vaginal fluid
Atypical virus = retrovirus (RNA)

38. See video at:
/sites/ /student_view0/chapter24/animation__how_the_hiv_infection_cycle_works.html

39. 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.
Eventually, it reduces the number of lymphocytes’ and their ability to create antibodies.
HIV leads to AIDS, where the immune system fails.

44. 90 day journey