MICROBIOLOGY – ALCAMOChapter 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

.

• Useful, Up to a point!

• Pathogens sensitive to heat, so are we

• Permanent Damage/Death 106/107

• Treat to lower fever @ 102, call doctor

Fever

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

•Actions of Complement: –Weakens cell membranes

–Attracts phagocytes

–Stimulates Inflammation

•Stimulated by antibody/antigen activity

Complement System

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