Microbiology Chapter 16: Innate Immunity

Goal of immunity

survey the body for foreign organisms or molecules

recognize and destroy foreign material

create a memory response to this foreign material

Innate immunity

nonspecific defense present at birth

no memory response, faster response

first and second lines of defense

Adaptive Immunity

specific defense (specific response to specific microbe)

that adapts or adjusts to handle a particular microbe

has memory, slower response

third line of defense

What mechanisms are part of the first line of immune defense?

intact skin

mucous membranes + secretions

normal microbiota

antimicrobial substances (chemical factors)

What mechanisms are part of the second line of immune defense?

phagocytes

inflammation

fever

What mechanisms are part of the third line of immune defense?

specialized lymphocytes (T cells and B cells)

antibodies

Physical barriers to prevent microbial entry

skin and mucous membranes

Parts of skin

dermis (inner, thicker portion composed of connective tissue)

epidermis (outer, thinner portion, w/ keratin, a protective protein in top layer of epidermal cells)

Where are mucous membranes

Lining GI, respiratory, genitourinary tracts

What do the epithelial layers of mucous membranes secrete?

Mucus, a thick fluid containing glycoproteins

Function of mucus

keeps tracts from drying out

allows for things to get trapped so can be collected + dealt with

Flushing mechanisms of the first line of defense

lacrimal apparatus

saliva

ciliary escalator

perspiration

urine, defecation, vomiting

Function of lacrimal apparatus

drains + produces tears

prevents microbes from settling on the eye

Definition of lysozyme

enzyme found in perspiration and saliva

breaks gram (+) cell walls

Ciliary escalator

mechanism where microbes trapped in mucus are propelled up towards the throat by cilia

What antimicrobial substances are found in saliva?

amylase and lysozyme

What are the components of gastric juices?

HCl

Enzymes

Mucus mixture

Low pH (VERY acidic)

pH range of vaginal secretions

pH 3-5

pH of urine

pH 6

Components of blood

Plasma + formed elements suspended in it

Some formed elements of blood

RBCs (erythrocytes)

Platelets

WBCs (leukocytes)

WBCs/Leukocytes

a vital part of the immune system that fights infection and disease

includes granulocytes and agranulocytes

granulocytes + examples

WBCs characterized by the presence of large granules in the cytoplasm

neutrophils, basophils, eosinophils

Neutrophils

phagocytes active in the initial stages of infection

most numerous WBC

Basophils

produce histamines

(chemicals important for inflammation and allergic responses)

Eosinophils

somewhat phagocytic

produce toxic proteins against parasites (ex helminths)

Agranulocyes

Do not have large granules visible in cytoplasm

Includes monocytes, dendritic cells, lymphocytes

Monocytes

agranulocytes that can mature into macrophages, which are phagocytic

Dendritic cells

derived from monocytes

phagocytic

initiate the adaptive immune response

Lymphocyte varieties

NK cells (innate immunity)

T cells + B cells (adaptive immunity)

NK cells

“natural killer cells”

attack cells that display abnormal cell membrane proteins

by releasing perforin and granzymes upon binding

Perforin

pore-forming protein causing channels in cell membrane

leads to lysis (cytolysis)

Granzymes

protein-digesting enzymes that induce apoptosis

Apoptosis

programmed cell death

“self destruct mechanism”

so wrong cell doesn’t “ruin it for everyone”

Definition of phagocytes

cells that perform 'cellular eating' and perform an important initial response

What type of cells are phagocytes?

white blood cells (WBCs) or derivatives of WBCs

Chemotaxis

chemical attraction of phagocytes to microbes

Phagocytosis main phases

chemotaxis

adherence

ingestion

digestion

What can cause chemotaxis?

chemical signals can be:

microbial products

damaged tissue cells

cytokines

Phagocytosis adherence and results

attachment of a phagocyte's cell membrane to microbe surface

facilitated by PAMPs to TLRs

binding initiates phagocytosis

can induce release of cytokines to recruit more phagocytes

Facilitation of adherence

by pathogen associated molecular patterns (PAMPs) on antigen

to toll-like receptors (TLRs) on phagocyte

(ex protein / carb pattern on microbe binds to receptor on phagocyte)

PAMPs

(Pathogen Associated Molecular Patterns)

molecules on microbes recognized during adherence

TLRs

(Toll-like Receptors)

receptors on phagocytes that bind to PAMPs, facilitating adherence and initiating phagocytosis

Ingestion step of phagocytosis

pseudopods engulf the microbe

forming a phagosome (sac / vesicle / body used to eat)

which pumps in H+ (lowering pH) to activate hydrolytic enzymes

What happens during the digestion step of phagocytosis?

the phagosome fuses with a lysosome (body involved in breaking things down)

which forms a phagolysosome

enzymes released to break down microbe

Types of enzymes available to break down microbe in the phagolysosome

lysozyme (hydrolyzes peptidoglycan)

lipases, proteases, and nucleases

Last part of digestion

bacteria is destroyed

waste is discharged

Functions of inflammation

to destroy the injurious agent + byproducts

if destruction not possible, to limit the effect on the body by confining it

to repair or replace damaged tissue

Inflammation process

after tissue damage histamine release causes vasodilation

diapedesis

phagocytes destroy microbes

pus forms

tissue repair

Vasodilation

dilation of blood vessels

Effects of vasodilation

increases blood flow

increases permeability

Increased permeability benefits

allows defensive substances and clotting factors to pass through blood vessel walls

so can enter injured area

blood clotting prevents spread of microbe + toxins

Diapedesis

process where phagocytes squeeze between endothelial cells to reach the damaged area

Cause of pus formation

occurs when phagocytes and microbes die

resulting material pushes to the surface of the body or absorbed gradually