intro to micro unit 4, part 1

Immunity

your body’s ability to fight off disease

Innate immunity

built-in, nonspecific, immediate defenses you’re born with

First line of defense

Physical & Chemical Barriers

Physical barriers

• Skin

• Mucous membranes

• Ciliary escalator

• Tears & saliva

• Urine flow

• Fever

Skin

tough outer shield

Mucous membranes

trap microbes

Ciliary escalator

tiny hairs move mucus and trapped microbes out of the lungs

Urine flow

flushes microbes out

Fever

heat. slows microbe growth

Chemical barriers

• Lysozyme

• Stomach acid

• Vaginal acidity

• Sebum

• Transferrins

Lysozyme

in tears, saliva, sweat kills bacteria

Stomach acid

(very low pH) destroys microbes

Vaginal acidity

prevents growth

Sebum

contains fatty acids that inhibit fungi

Transferrins

bind iron so bacteria can’t use it

Biological barrier

Normal microbiota (good bacteria)

Normal microbiota (good bacteria)

competes with pathogens for space and nutrients

• overusing antibiotics can remove this protection

Second line of Defense

Innate Immune Cells

• main white blood cells

Main white blood cells

• Neutrophils

• Macrophages

• Dendritic cells

• Basophils

• Eosinophils

• NK cells

Neutrophils

fast responders; main phagocytes

Macrophages

from monocytes — big eaters; clean up tissues

Dendritic cells

activate the adaptive immune system

Basophils

release histamine (inflammation)

Eosinophils

attack parasites

NK cells

kill infected or abnormal cells

Phagocytes

Neutrophils, macrophages, dendritic cells

What do phagocytes do?

ingest and destroy microbes

Inflammation

body’s response to injury or infection

What you see in inflammation

• redness

• heat

• swelling

• pain

why inflammation happens

• brings immune cells to the area

• contains and kills pathogens

• starts tissue repair

Steps of Inflammation

1. Acute phase

2. Vasodilation

3. Marination

4. Diapedesis

5. Tissue repair

Acute phase (inflammation step)

proteins release

Vasodilation

blood vessels widen → redness/heat

Margination (inflammation step)

WBCs stick to vessel walls

Diapedesis (inflammation step)

WBCs squeeze out into tissues

Fever

triggered when immune cells release IL-1, resetting hypothalamus to a higher temperature

• slows microbe growth and boosting immune activity

• too high can cause dehydration, delirium, or worse

Complement system

group of 30+ proteins in blood and is activated by antibodies or microbes themselves

Classical pathway of complement system

activated by antibodies

Alternative pathway of complement system

activated by microbes themselves

Results of complement system

• cytolysis

• inflammation

• enhanced phagocytosis

Cytolysis

bursting microbes

Interferons

antiviral proteins made by lymphocytes and macrophages after virus detected

• inhibit viral replication

Interferon: IFN-$\alpha$ & IFN-$\beta$

made by virus-infected cells

• warn neighbors to block viral replication

Interferon: IFN-$\gamma$

made by lymphocytes

• activates macrophages and neutrophils