Lecture 23- Intro to Immune System, Innate Immunity, Barriers

The human immune system

copy flow chart

2 Types of Immune System

1) innate immunity

2) adaptive immunity

Innate Immunity

non specific, constitutive, inherent to the host

Types of Innate Immunity

1) First line of Defense (pre invasion)- mechanical, barrier, chemical or biochemical, microbiome

2) second line of defense (post invasion)- phagocytosis, inflammation, complement

Adaptive Immunity

specific, inducible, acquired upon exposure to pathogen

Types of Adaptive Immunity

antigen processing and presentation, antibodies, cell mediated cytotoxicity

3 Properties of the First Line of defense

1) general defense common to all healthy individuals

2) always present and effective against most microbes

3) fast and immediately operative

Physical Barriers or Mechanical, First Line Defense

skin, air and urine flow, tight cell junctions (epithelial cells)

Chemicals, First Line Defense

toxic organic acids, reactive oxygen and nitrogen species

Peptides and enzymes in secretions, First Line Defense

defensins, lactoferrin, lysozyme, lactoperoxidase

Mucus, First Line Defense

mucin secretions

Microbiota, First Line Defense

competition with pathogens, provide nutrients

Barriers, First Line of Defense

physical structures, chemicals, and processes that work to prevent pathogens from entering the body

4 Different Types of Barriers

1) skin

2) lacrimal apparatus

3) mucous membranes

4) resident microbiota

Skin Barrier

layer of dead skin, oily sweat glands

Lacrimal Apparatus Barrier

tear ducts, eyes

Mucous Membranes Barrier

of the resp, digestive, urinary and reproductive systems

Resident Microbiota Barriers

important first line of defense

Microbial antagonism

microbiota compete with potential pathogens

How does the Microbiome Make it hard for Pathogens to Thrive? 7

1) competing for access to nutrients

2) creating an environment unfavorable to other microbes

3) preventing pathogens from attaching to host cells

4) helping to simulate the body’s second line of defense

5) generating antimicrobial compounds

6) promoting overall health by providing vitamins to host

7) generating compounds that modulate immunity

Examples of Mechanical First Line Defense of Host

1) removal of particles including microorganisms by rapid passage of air over cilia in nasopharynx

2) flushing of urinary tract prevents colonization

3) mucus, ciliated cells lining trachea suspend and move microbes out of the body

4) lactoferrin in tears and other mucous secretions sequester iron and prevent bacterial growth ( and chemical/biochemical)

5) lysozyme in tears and mucous secretion degrades peptidoglycan in bacterial cells walls ( and chemical/biochemical)

Examples of Microbiome First Line Defense of Host

1) skin, produces antimicrobial FAs, normal resident microbiota inhibit pathogen colonization (and chemical/biochemical)

2) normal microbiota compete with pathogens in gut

3) normal microbiota compete with pathogens in urogenital tract

4) intestinal epithelial cells create a uniform physical barrier in the gut (also chemical/biochemical)

Chemical/ Biochemical First Line of Defense of Host

1) stomach acidity and digestive enzyme inhibit microbial growth

2) host digestive enzymes and bile salts inhibit microbial growth

3) blood an lymph proteins inhibit microbial growth

Skin as Line of Defense

skin microorganisms are associated primarily with sweat or fat glands and hair follicles, some bacteria and fungi but not viruses can grow on surface especially if moist

Innate Defenses of SKIN

1) physical barrier

2) dry to prevent microbe growth or replication

3) cooler than body, less than 37C

4) acidic, pH5

5) sweat glands, sebaceous fat glands, and hair follicles

6) normal resident microbiota

7) SALT, skin associated lymphoid tissue

8) desquamation

9) major resident skin microbes are gram pos Staph epidermis and P. acnes

Physical Barrier of Skin

dead keratinized layer of skin epidermis derived from keratinocytes, difficult for bacteria to digest

Sweat and Sebaceous Glands, and Hair Follicles of Skin

secretion of oily sebum containing toxic lipids, organic FAs, defensins, lysozymes that kill microbes or prevent microbe growth/replication

Normal Resident Microbiota of the Skin

mostly gram pos. bacteria, compete with pathogens for colonization of environmental niche

SALT skin associated lymphoid tissue, Skin

comprised of phagocytic cells, T and B cells that produce IgA and initiate immune response functioning with protective immunity

Desquamation of Skin

active sloughing of cells to remove attached bacteria

S. epidermis and P. acnes of Skin

P. acnes is gram pos, anaerobic bacillus that colonized sebaceous fat glands, easily sebum, overgrowth causes acne, P. acnes helps generate low pH protective against other microbes

Lacrimal Apparatus

portal of entry, plays role in mechanical/physical and chemical/biochemical defenses

Mechanical/physical Defenses of Lacrimal Apparatus

produces and drains tears, blinking spreads tears and washes surface of the eye

Chemical/biochemical defenses

lysozyme in tears destroys bacteria, lactoferrin in tears sequesters iron to prevent bacteria growth, viruses can be more resistant to these factors

2 Mechanisms of Bacteria Killing Lysozymes

1) hydrolysis of peptidoglycan, main function

2) forming pores in lipid bilayer of the cytoplasmic membranes

Innate Immune Properties of Lactoferrin

1) sequesters iron away from microbes

2) anti-bacterial

3) immunomodulatory

4) anti-viral

5) cytoprotective effect

6) anti-cancer

7) anti inflammatory

First Line of Defenses in Gut

GI tract offers different environments, different microbes can be associated with the different areas, most are stricut or facultative anaerobes

Innate defenses of the GI Tract

1) acidity

2) digestive enzymes

3) fast flow of contents

4) absorption of nutrients

5) bier salts

6) mucus are sloughing of cells

7) Paneth cells

😎 persitalsis and rapid flow content

9) absorption of bile acids, vit B12, and onteher nutreints in contacnt

10) slow flow of contents

Acidity of GI Tract

secretion of acid HCl that most bacteria can’t survive without protection

Bile Salts of GI tract

disrupt membranes of microbes and viruses

Mucus and Sloughing Cells of skin

goblet cells secretes mucin, removes attached microbes

Barrier Function

collective ability by host to prevent access or pathogens

Barrier Function

collective strategies used by host to prevent acess of pathogens to the underlying cayses

Host Innate Barriers to Infection Include…?

1) mechanical and physical barriers

2) chemical and biochemical barriers

4) resident microbiota