B3: innate immunity - anatomical barriers and complement system

what aspects of the skin make it an effective defensive barrier?

tightly packed, dead epithelial cells

dry → microbes need moisture to grow

constantly sloughing off our outer later of dead skins cells (mechanical removal) → microbes can’t attach to our skin

large amounts of keratin: tough, durable protein → most microbes can’t digest keratin

where are mucous membranes found?

epithelium lining the gastrointestinal, respiratory, and genitourinary tracts

what do mucous membranes secrete?

mucus

what is mucus beneficial for?

glycoprotein that keeps the membrane moist

keeps live cells from drying out

allows for nutrients to be brought in and waste to be sent out

where do most infections occur?

most infections occur through mucous membranes

• thin layer of dead cells

• more vulnerable to attack

what are other defenses of mucous membranes?

epiglottis

nose hair

what does the epiglottis do?

prevents food from entering the respiratory tract

what do nose hairs do?

filters incoming air, removes microbes

• get stuck in the mucus in your nose hairs so they don’t get in your lungs

what do tears do to physically prevent infection?

constantly wash the surface of the eye

• water

• mucus

• lipids

where do tears go?

drain into the nose/throat

what does irritation in your eye cause?

increases tear production (mostly water)

what does saliva do to physically prevent infection?

keeps the mouth moist and washes bacteria off surfaces

what does peristalsis do to physically prevent infection?

keeps substances moving along

what does defecation do to physically prevent infection?

removes materials from the intestines

infecting bacteria must find a spot to attach or they will simply pass through us

what does skin sloughing do to physically prevent infection?

microbes can’t attach to our skin

what does urination do to physically prevent infection?

washes unattached bacteria away

what do vaginal secretions do to physically prevent infection?

move unwanted microbes out

how does the respiratory tract prevent infection?

mucus produced in the lungs trap most bacteria

what removes the bacteria in your lungs?

removed by ciliated epithelium

where does the trapped bacteria go?

ciliary escalator moves trapped bacteria up and out

• mucus gets moved up and grabbed by the next set of cilia until you clear your throat

• goes down to your stomach

sneezing/coughing will also remove mucus

what is a lysozyme?

antibacterial enzyme found in sweat, saliva, and tears

how does lysozymes attack bacteria?

digests peptidoglycan cell walls

are skin oils protective?

short fatty acids that are toxic to most microbes

insert themselves into bacterial membranes and reduce their capacity for growth

how is the stomach effective to killing bacteria?

gastric acid in the stomach: very acidic

kills most bacteria

why are acid blockers a potentials problem for infections?

stops acid production

get food-borne infections more

what are defensins?

small antibacterial proteins

found in sebum, saliva, tears, and mucus in the lungs

how do resident intestinal bacteria protect against infection?

block attachment

inhospitable environment

how do resident intestinal bacteria block attachment?

take up available attachment sites

how do resident intestinal bacteria make it an inhospitable environment?

use up available nutrients/resources

produce antibacterial chemicals

change the environment

give an example of resident intestinal bacteria producing antibacterial chemicals

E. coli produces anti-Salmonella compounds

give an example of resident intestinal bacteria changing the environment

lactic acid bacteria in the vagina produce acid byproduct from their metabolism

make it a slightly acidic environment → yeast does not like this

do anatomical barriers require any prior exposure to a pathogen to protect against it?

no!

jules bordet discovered 2 factors (in plasma) that killed bacteria, what were they?

heat-stable (heat-resistant) factor

heat-labile (heat-sensitive) factor

what was the heat-stable (heat-resistant) factor?

killed specific bacteria

turned out to be antibodies

what was the heat-labile (heat-sensitive) factor?

killed non-specific bacteria

complement

what is the complement?

defensive proteins found in the blood, act in a cascade to respond to pathogens

system of over 30 proteins

can complement recognize some pathogens without have been exposed previously?

yes!

what are the key facts about complement?

present at birth, genetically determined

recognizes certain molecules as “non-self”

capable of attacking cells marked by these molecules

what signals set off complement?

antibodies

foreign substances

how do antibodies set off complement?

complement reacts to presence of multiple antibodies bound to a surface (adaptive immunity)

how do foreign substance set off complement?

has proteins that recognize certain characteristic bacterial proteins/carbohydrates

the targeting of complement to foreign surfaces is in place at birth and never changes

define PAMP

pathogen-associated molecular patterns

non-host molecules that are commonly associated with pathogens

examples of PAMPs

lipopolysaccharides, peptidoglycan, etc.

when do PAMP receptors develop?

receptors for recognition of PAMPs are present at birth as a key part of the innate immune system

what are the 3 responses when the complement system recognizes an intruder?

opsonization

cytolysis

inflammation

what opsonization?

coating of an object with immune system proteins

what does opsonization promote?

phagocytosis → makes it easier for phagocytic defenses to see the marked cells

if they spot something coated in complement → they’re going to kill it

what is cytolysis?

punches holes in the plasma membrane

lyses cells

how does complement cause inflammation?

signals for inflammatory response

also attract phagocytic cells

what happens when a complement recognizes that it’s bound to a target that shouldn’t be there?

complement system has protein members that are cytokines (cell signals) that send out an inflammatory signal

region becomes inflamed

immune system focuses its attention on that region

does complement act only on its own, or can it also act to enhance adaptive immunity?

enhances adaptive immunity by recognizing antibody-bound objects