The Immune
System
Chapter 21\

Innate Defenses
!

Innate: structural defenses; responds to nonspecific foreign substances
" First

line: external surface epithelium & membranes
" Second line: inflammatory processes – antimicrobial proteins, phagocytes, etc.

First Line Defenses
!

Skin
"
"

!

Mucous Membrane
"

!

physical barrier to microbes
Keratinized. Keratin is resistant to most bacterial enzymes & toxins physical barrier & produces a variety of protective chemicals

Protective chemicals produced
" Acid, enzymes, mucin, defensins, and other chemicals Second Line Defenses
!

Phagocytes attack after pathogens get through first line defenses
" Macrophages:

derived from monocytes and do most

work
!
!

Free Macrophages: roam through tissues
Fixed Macrophages: permanent residents in particular organs " Neutrophils:

most common WBC

Phagocytosis
!

Phagocytic mechanisms:
" Phagocyte

engulfs pathogens by using opsonins
! Compliment proteins allowing phagocytes to bind to pathogens (opsonization)
" Ingestion: formation of phagolysosomes
!

!

!

Respiratory Bursts: merge phagosome with lysosome & flood phagolysosome with free radicals (macrophage)
Defensins are used to pierce the pathogen's membrane

Phagocytosis occurs when phagocytes engulf pathogens

Phagocytosis

Figure 21.2

NK Cells – White Police
!

Natural Killer Cells:
" Small

population of large granular lymphocytes that kill cancer and virus-infected body cells
" Non specific, attacking general abnormalities
" Not phagocytic: attack is directly contacting the target cell ! Apoptosis- programmed cell death
!

Shortly after perforation the target nucleus disintegrates.

" Release

chemicals that enhance the inflammatory response Inflammation
!
!
!

Inflammation- tissue response to injury
Inflammation response is triggered by injury – trauma, heat, chemical irritation, infection, etc.
Beneficial effects
" Prevents

!

spread of damaging agents to nearby tissues
" Disposes of cellular debris & pathogens
" Promotes repair
" Alert the adaptive immune system
Cardinal signs: redness, heat, swelling, pain, and impaired function
" Impaired function forces rest to aid in healing

Inflammatory Chemical Response
!

Starts with an alarm triggered by Toll-like receptors (TLRs) and flooding of chemicals from the mast cells occurs
"

"

Histamines are released by the mast cells
! potent inflammatory chemical
Three other inflammatory chemicals are Kinins, Prostaglandins, and Complement
! Dilate local arterioles and make capillaries leakier

Vasodilation
!

Redness and heat of inflamed region due to hyperemia
" Congestion

with blood occurs when arterioles

dilate
" Edema caused exudate leaking from blood into tissue spaces causing pain
" Pain also associated with bacterial toxins & some mediators (Kinins and Prostaglandins)

Innate, Internal Defenses:
Inflammatory Response
!

Edema (swelling) is not only bad
" Sweeps harmful substances into lymphatic system " Enhances entry of clotting protein
! Enhances with complement and clotting factors Events in
Inflammation

Figure 21.3

Phagocyte Mobilization
!

!

Phagocyte mobilization: infiltration of damaged area lead by neutrophils & followed by macrophages There are four steps to Phagocyte infiltration
" Leukocytosis
" Margination
" Diapedesis
" Chemotaxis

Phagocyte Mobilization
Leukocytosis: leukocytosis-inducing factors released by injured cells promote rapid release of WBCs from red bone marrow
"Neutrophils enter from red blood marrow and increase fourfold to five-fold
! Margination: increased vascular permeability causes decreased fluid in vessels; blood flow slows & neutrophils are able to move to vessel margins. Here endothelial markers (CAMs) allow neutrophils to cling to vessel walls
"Margination- phagocytes clinging