MICROBIOLOGY – ALCAMO
Chapter 18 – Resistance and the
Immune System
Defense Mechanisms
• Specific Resistance
– Come about in response to a particular
parasite
– Directed solely at that parasite
• Nonspecific Resistance
– Exists in all humans
– Present from the earliest time of life
Nonspecific Resistance
• Depends on the well-being of the
individual and proper functioning of
body systems
• Factors involved:
– Nutrition
– Fatigue
– Age
– Sex
– Climate
Nonspecific Resistance
• Species Immunity – diseases
affecting one species will not affect
another
• This type of immunity is based on
– Physiological differences
– Anatomical differences
– Biochemical differences
• Example – chickens are resistant to
anthrax because their body
temperature is higher than ours (450 C)
Nonspecific Resistance
• Behavioral Immunities – exist
among various peoples of the world –
way of life
• Example – India in 1700’s, people did
not keep water in their houses, so
mosquitoes couldn’t breed and spread
malaria
Nonspecific Resistance
• Racial Immunities – reflect the
evolution of resistant humans
• Example – people in Africa with sickle
cell anemia do not get malaria because
the parasite can not enter the distorted
RBC’s
Mechanical Barriers
•
Skin and mucous membranes that
extend into our body cavities
•
Disease is rare unless these barriers
are penetrated
•
But, skin is penetrated every day:
–
Cuts
–
Bug bites
–
Injections
Mechanical Barriers
•
Associated defense chemicals:
–
Low pH – stomach and vaginal tract
–
Lytic enzymes (lysozyme) - in human
tears and saliva – digest Gram + bacteria
–
Bile – from the gall bladder
–
Interferons – proteins produced by cells
in response to viruses
Cellular Protection
• Theory of Phagocytosis – Metchnikoff
(1884, Ukraine)
• Involves cells called phagocytes:
– Chemical attraction (chemotaxis) occurs
between the MO and the phagocyte
– Phagocyte invaginates and pinches in to
form a phagosome
– Phagosome fuses with a lysosome that
has digestive enzymes and acidic pH to
digest MO
– Waste materials are expelled
Cellular Protection
•
Phagocytosis – Ameba-Like
– Surround and digest MOs
Phagocytosis Video (1 minute)
Dnatube video - phagocytosis
Inflammation
Inflammation
• Nonspecific defensive response to
tissue damage
• Can be due to an injury, blow to the
skin, bee venom, UV radiation, MO’s
• Signs of inflammation:
– Rubor – red coloration from blood
– Calor – warmth from heat of blood
– Tumor – swelling from fluids
– Dolor – pain to the local nerves
Inflammation
• An irritant sets into motion a process
that will limit the extent of the injury
and repair tissue damage
– Dilation of blood vessels – flow of plasma
into the tissue and fluid accumulation
– Phagocytes (neutrophils and
macrophages) enter the injured area to
attack the irritant
– Pus accumulates and can form an abscess
or boil
•Pus = Dead WBC, MOs and Tissue
•Greatly stimulated by B & T Cells
Fever
•
Abnormally high body temperature
•
The brain’s hypothalamus region
maintains a body temperature of
about 98.60C
•
Exposure to “Pyrogens” resets the
thermostat higher
•
Fever inhibits the growth of certain
MO’s
Fever
•
Useful, Up to a point!
•
Pathogens sensitive to heat, so are we
•
Permanent Damage/Death 106/107
•
Treat to lower fever @ 102, call doctor
Complement System
• 11 small blood (serum) proteins
made in the liver
• Help antibodies and phagocytes
to clear MO’s from an organism
•
Attack anything with a cell
membrane
Complement System
•Actions of Complement:
–Weakens cell membranes
–Attracts phagocytes
–Stimulates Inflammation
•Stimulated by
antibody/antigen activity
Natural Killer (NK) Cells
• Unique group of defensive cells that
roam the body in blood and lymph
• Type of cytotoxic lymphocyte
• Kill cancer cells and virus-infected cells
before the immune system is activated
• They kill cells by releasing small
cytoplasmic granules of proteins that
cause the target cell to die
Two Natural Killer Cells Attack a Cancer
Cell