Chapter 12 Host Defenses

Innate defenses

non-specific” defenses used to protect the body from any general pathogenic attack

(This includes two main lines of defense)

• Barriers to prevent infection

• Systems to combat infections

Acquired defenses

specific defenses used to protect the body from pathogens identified by the body

Immunology

study of acquired and innate defenses

barriers

 prevent pathogens from infecting the body (first line of defense)

• defend against dust, smoke

skin (first line defense)

physical barrier

• Most things exist outside the body and can’t get in

Cilia and mucus

respiratory system trap and then push out inhaled particles

Microbiome

can physically occupy space to prevent pathogens from attaching to body surfaces

chemical (first line defense)

Lysozyme

Lysozyme

 a chemical found in tears and saliva (among others) that hydrolyzes bacterial cell walls

•  makes it harder for pathogens to invade through the eyes or digestive tract

Second Line of Defense

kicks in when a pathogen gets beyond the first line

•  mostly chemical rather than physical responses

Cells second Line of Defense (chemical)

phagocytes

Chemicals second Line of Defense (chemical)

interferons and the Complement system

Processes second Line of Defense (chemical)

inflammation and fever

Blood is composed of two main things:

Plasma, (Formed elements, which are not ‘soluble’):

1. Erythrocytes (aka RBCs)

2. Leukocytes (aka WBCs)

3. Platelets

Granulocytes (White Blood Cells (WBCs))

leukocytes that contain large granules (visible during staining of blood)

Basophils (White Blood Cells (WBCs))

make and release histamine

Eosinophils (White Blood Cells (WBCs))

perform phagocytosis and diapedesis

Neutrophils (White Blood Cells (WBCs))

perform phagocytosis and diapedesis

diapedesis (occurs in Eosinophils and Neutrophils)

movement of WBCs outside the blood vessels

Agranulocytes (White Blood Cells (WBCs))

eukocytes that do not contain large granules

Monocytes (White Blood Cells (WBCs))

mature into macrophages

Lymphocytes (White Blood Cells (WBCs))

 responsible for the specific immune response

• B-Lymphocytes

• T-Lymphocytes

• Natural Killer cells

ratio of white blood cells (from highest to lowest)

Neutrophils > lymphocytes > monocytes > eosinophils/basophils

• (never let monkeys eat bananas)

Differential White Blood Cell Count

test to measure the ratio of WBCs

• if changes- indication of infection or disease

Eosinophilia (Differential White Blood Cell Count)

allergies or parasitic worm infection

• (increased Eosinophils)

Phagocytosis

process by which cells of the immune system engulf invading cells to break them down

5 steps of Phagocytosis

1. Chemotaxis

2. Adherence

3. Ingestion

4. Digestion

5. Elimination

mechanisms of second line of defense

1. Phagocytosis

2. Extracellular killing by Leukocytes

3. Nonspecific Chemical Defenses

4. Inflammation

5. Fever

Chemotaxis

movement of a cell in response to a chemical stimulus

1. Cells called phagocytes use  pseudopods (extensions of the membrane and cytosol) to move towards invading microbes

Adherence

recognition and attachment of the phagocyte to the invading cell

• (just like in viruses)

Ingestion

pseudopods extend from the phagocyte to surround the microbe

• forms a phagosome

Digestion

how the macrophage breaks down the invader that it swallowed

•  involved the fusing of the phagosome with a lysosome

Elimination

macrophages will eliminate the debris by exocytosis

• phagosome will fuse with the cell membrane, spilling the broken down pathogen out of the cell

Phagocytes such as Macrophages are attracted by:

1. Microbial waste products or secretions

2. Components of damaged cells or tissues

3. “Chemotactic Factors”: specific chemicals in the complement system

4. Cytokines: chemicals released by WBCs during an immune response 

   (kine = movement)

Pathogen-Associated Molecular Patterns (PAMPs) (Adherence)

things that might be recognized by a receptor protein on the macrophage

(PAMPs include:)

• Bacterial flagella

• Peptidoglycan

• Lipopolysaccharide

Phagocytes can also recognize ‘tags’

attached to an invader by the immune system

Complement system

weries of proteins that come together to form a “Membrane Attack Complex” (MAC) that perforates the membrane of invading bacteria

• more effective against gram negative

Interferon

a chemical that is used during a viral infection

•  released by cells infected by a virus as an ‘alarm bell’

• stops translation

inflammation

Blood vessels dilate

(Why?)

• stimulates the migration of phagocytes

• more likely a pathogen will be killed

• (Chronic inflammation is long term, can lead to tissue damage over time)

fever

When the body temperature rises over 37C,

pyrogens (fever)

chemicals that trigger the hypothalamus to increase body temperature

various types of pyrogens

• Bacterial toxins

• Cytoplasmic contents of bacteria released by lysis

• Certain interleukins (chemicals released by lymphocytes)

Good Fever

• It increases the activity of interferons

• It inhibits the growth of mesophilic microbes

• It may enhance the performance of certain immune cells

Bad fever

Too high for too long can damage the host cells

• (we are mesophiles too)

• Some organisms prefer a slightly-warmer-than-us temperature (ebola)