Immunology

3 Layers of Defense

1. Barriers

2. Innate Immune System

3. Adaptive Immune System

Immunity

The ability to resist organisms or toxins that tend to damage tissues and organs

Keratinocytes

Produce cells of the outermost layer of the epidermis of skin

Stratum Corneum

Dead, tightly layered and cornified squamous cells (thick hardened tissue)

Function: Create a watertight barrier to prevent dehydration

Create a microbe-inhospitable dry environment on the surface of skin

Mucous Membranes

Lines all of the body's cavities that come into contact with the environment

Respiratory Tract (Physical)

Mucus traps inhaled bacteria, fungi, and other particles

GI Tract (Physical)

Mucus and mucous membranes help protect epithelial cells and underlying tissues from damage,

How? Through digestive enzymes and propelling ingested matter through the tract

Respiratory Tract (Hair)

Hair-like cilia in the epithelial lining to help keep it clean by moving secretions with microbes and particles out (coughing & sneezing)

What disrupts cilia in the respiratory tract?

smoking & alcohol -> increased risks of respiratory infections

B-defensins

Make microbes more susceptible to ingestion and destructions by phagocytic cells by secreting microcidal molecules

Cystic Fibrosis

A mutant gene that causes abnormally thickened and viscous secretions that block the respiratory tract

Bacteria: Pseudomonas aeruginosa

Why is skin a good chemical barrier?

- low pH

- contains a/B defensins, cathelicidin, fatty acids

- sweat, enzymatic activity = inhibit microbial growth

• Molecules with enzymatic activity: Lysozyme, RNases, DNases

Sloughing

Constant from the stratum corneum that removes microbes attached to cutaneous surfaces

Genitourinary Tract

Urination helps inhibit movement of microbes from the environment up into the bladder & kidneys

Females: protected by vaginal acidic secretions and microcidal molecules secreted by the mucous membranes

Respiratory Tract (Chemical)

Respiratory epithelium cells secrete microcidal molecules (B-defensins)

Makes microbes more susceptible to ingestion and destruction by phagocytic cells

GI Tract (Chemical)

Very acidic

Digestive enzymes: effective in killing & degrading potential pathogens that may be ingested

Lacrimal Gland

Secretes 3 aqueous layers of the tear film

Tear Film

• Eye’s 1st line of immune defense

• Aqueous layer with antimicrobial components (LLABB)

• Lysozyme

• Lactoferrin

• Secretory IgA

• B-defensins

• Blinking mechanically clears debris, pathogens, and redistributes tear film across the surface

Lysozyme

Broad-spectrum antibacterial enzyme, highest concentration of any body fluid

Lactoferrin

Binds free iron, starving bacteria of a needed nutrient

Secretory IgA

Secreted by conjunctival plasma cells

Mucosal antibody of the ocular surface

B-defensins

Broad antimicrobial peptides also found in skin and respiratory tract

Purpose of Blinking

Mechanically clears debris and pathogens; redistributes tear film across the surface

Dry Eye Disease

Reduces tear volume and antimicrobial content, increasing risk of eye infections

Contact lens wear

• Disrupts the normal ocular surface barrier

• Reduced corneal oxygenation and tear exchange under the lens

• Biofilm on lens surface esp with long wear and bad hygiene

• Major risk for eye infections, especially with overnight wear

Clinical Pearl

Barrier-focused counseling (lens hygiene, treating dry eye, lubrication) is an immunologic intervention

Commensal Microbes

• Microbes that exist in a symbiotic relationship with the body

• Ex) skin and GI tract (digestion)

• Make up more than 95% of normal cells

• DEFEND the territory and inhibit the establishment of other potential pathogenic microbes

When are Commensal microbes pathogenic?

• immunocompromised

• Intro of medical devices (catheters) into the body → Commensal bacteria enters the skin and areas that are typically sterile

• Disruption of flora → disease

• Ex yeast infection after a course of broad-spectrum AB therapy

Innate Immune System (LOW tech)

• 1st line of defense against infection

• Innate: existing from birth

• Fast & quickly mobilize preexisting molecules

• Protect against a WIDE range of infections by rapid destruction of infectious organisms, activation of phagocytic cells, and localized protective response (inflammation)

• No specificity (response is the same no matter the invader)

Adaptive Immune System (High tech)

• Developed over an individual’s lifetime, short-lived

• Can specifically distinguish self from non-self

• Anticipatory defense system of recognition molecules that interact with non-self antigens

• Gene rearrangement to generate large # of preexisting receptors that can identify any antigen

SDMC