BIOL 2401 Unit 8: Innate & Adaptive Immunity

First line of defense

Involves physical defense mechanisms such as skin, normal flora, and mucous membranes

Second line of defense

Activates after the first line of defense is breached. Includes fever, inflammation, and phagocytes

Third line of defense

Activates if non-specific/innate immunity fails. Includes T and B cells, antibodies

What composes the blood-brain-barrier, and what is its role?

Endothelial cells make up the blood-brain-barrier, and it functions to keep the brain and spinal cord sterile

Chemical factors in sebum

Low pH inhibits microbial growth (fatty acids)

Chemical factors in sweat

Lysozyme, salt, dermicidin (kills microbes)

Chemical factors in saliva

Lysozyme, lactoperoxidase, lactoferrin, IgA antibodies

What produces lactic acid in vaginal flora?

Lactobacillus

Competitive inhibition

Production of antimicrobial molecules (bacteriocins, lactic acid) and use of space and nutrients to prevent colonizaiton

Natural Killer (NK) cells

Lymphocyte (agranulocyte) that KILLS tumor cells or infected body cells. Releases perforin and granzymes in response to foreign antigens

Perforin

Toxic protein released by NK cells that punctures the membrane of an abnormal cell

Granzymes

Enzyme that digests protein through being poured into an abnormal cell, inducing apoptosis

If an NK cell recognizes MHC I on a healthy cell, what happens?

It recognizes the MHC I, and does nto kill the cell

If an infected cell does not present MHC I AND presents ligands for the activating receptor, what happens?

The NK cell attacks the infected cell, killing it

Two types of phagocytes

Neutrophils and macrophages

Steps of phagocytosis (CAIDW)

1. Chemotaxis → chemokines

2. Adherence → TLR to PAMP

3. Ingestion → Phagosome

4. Digestion → Phagolysosome

5. Waste removal

What substances induce chemotaxis?

Chemokines

Which structure on a phagocyte binds to a PAMP?

Toll-like receptors

Phagosome

Vesicle formed when a cell performs phagocytosis, holding the engulfed substance

Phagolysosome

Structure formed when a phagosome fuses with a lysosome for digestion

Physical effects of inflammation

Vasodilation and increased blood vessel permeability

Role of phagocytes in migration and phagocytosis

Phagocytes wall off microbes and destroy them

Which cells recognize pathogens, and chemicals do they produce?

Mast cells and resident macrophages recognize pathogens, and release histamine and chemokines

When does tissue repair occur?

When all harmful substances are eliminated from the injured area

Which cells stimulate fibroblasts for tissue repair

White blood cells stimulate fibroblasts

What causes granuloma formation?

Chronic inflammation, where the pathogens remain embedded in tissue

What is the role of pathogens and cytokines in fever?

They cause release of prostaglandins, resetting the hypothalamus to a higher temperature

Purpose of a fever

To inhibit bacterial growth and speed up body reactions to repair more quickly

Which complement protein leads to opsonization and activates C5?

C3b

Complement system

>30 plasma proteins that act in a cascade to help defend the body against invaders

C3

Central player of the complement system. Its point guard

Cytolysis

Bursting of a cell through too much water

Opsonization

Coating of a pathogen with opsonins, “tagging” them for destruction

Opsonization enhances which stage of phagocytosis?

Adherence

Which protein combines with C6, C7, C8 and C9 to form MAC leading to
cytolysis?

C5b

Why are G+ bacteria less susceptible to cytolysis?

Because of their thick peptidoglycan cell walls

Interferon

Type of cytokine made by cells during pathogen infection

Gamma interferon (IFN-γ)

Made by lymphocytes, activates macrophages and neutrophils to kill bacteria

Alpha and beta interferon (IFN-α and IFN-β)

Made by host cells infected with a virus. May diffuse to healthy neighboring cells, which are used to make antiviral proteins to disrupt viral multiplication

Iron-binding proteins

Proteins which “take iron away” from prokaryotes, inhibiting their growth

Lactoferrin

Iron-binding protein in tears

Transferrin

Iron-binding protein in blood and tissue fluids

Ferritin

Iron-binding acute phase protein in liver, spleen, and red bone marrow

Antimicrobial peptides (AMPs)

Short peptides (12-50 a.a.) which kill many microorganisms, including eukaryotic parasites

Modes of AMP action

1. Destroy DNA/RNA

2. Make pores in plasma membrane

3. Inhibit cell wall synthesis

Defensin

AMP produced by neutrophils which damage both fungi and bacteria cell membrane

How does E.coli kill pathogenic bacteria in the colon?

Through bacteriocin production

Complement protein cascade for cytolysis

C3 → C3b → C5 → C5b → C5b/C6/C7/C8/C9 (MAC)

Complement protein cascade for inflammation

• C3 → C3a → mast cell activation

• C3 → C3b → C5 → C5a → mast cell activation

Role of bacterial capsules in complement system evasion

Capsules can prevent MAC insertion, evading cytolysis

How do some gram-negative bacteria evade the complement system?

Through altering the structure of their outer membrane (LPS)

How do some G- and G+ cocci break down C5a, evading the complement system?

Through releasing an enzyme that breaks down C5a