Microbe Host Interactions

Lecture 2

explain how the human-microbe relationship is like a human life relationship

the body has multiple protective factors that keep pathogens out of the body to prevent us from getting sick, much like a fence or dog protect strangers from breaking into a home. A police car is like white blood cells in the immune system are like cop cars stopping crazy people

what is the innate immune system

present from birth and ready to work

it has no memory

three lines of defense

first line of defense

blocks invasion at the portal of entry

doesn’t involve recognition, very generally acting

ex: Skin, Mucous membranes, Tears, saliva (contain lysozyme), Stomach acid

second line of defense

internalized system of protective fluids and cells

involved inflammation and phagocytosis

acts very quickly at the local and systemic levels

third line of defense

acquired on an individual basis as lymphocytes find foreign substances

produces unique protective substances and cells that help if the certain microbe is encountered again

long term immunity

B cells and T cells

primary physical and chemical defense barriers

sebaceous glands

tears

mucus

saliva

cillia

mucus

wax

skin

sweat

stomach acid

intestinal enzymes

feces

urine

skin as a primary defense barrier

full of keratin, cemented together and hard to pass through

thick and tough

outer layers constantly shed, taking the microbes with them

sebum on the skin has an antimicrobial effect

mucus as a primary defense barrier

moist and permeable

barrier protection without the keratin

stops the entry and attachment of bacteria

blinking and tears get rid of eye irritants

saliva carries microbes to the stomach acid to die

lysozyme

in tears, saliva, and sweat

hydrolyzes the cell walls of bacteria

respiratory tract as a primary defense barrier

nasal hairs trap big particles

flowing of mucus and fluids during allergies and colds flushes microbes out

ciliated epithelium moves foreign particles in mucus to the pharynx to be removed

genitourinary tract as a primary defense barrier

urinating flushes out the urethra

vaginal discharge cleans out the lower reproductive tract in females

vagina is acidic

semen is antimicrobial

resident microbiota

blocks access of pathogens to the skin surface

creates unfavorable environment for pathogens

trains host defenses in a way to keep commensals in check and kill pathogens

what happens when the first line of defense is breached in the immune system

the second line of defense gets to work

surveys the body, recognizes and kills foreign material

primary lymphoid organs

red bone marrow and thymus

secondary lymphoid organs

lymph nodes

spleen

S A L T, M A L T, G A L T (connective tissue framework)

where are all blood cells made

bone marrow of long bones

hematopoesis

blood is made

thymus

triangle structure in the upper thoracic region

T lymphocytes mature here

using thymic hormones, T lymphocytes develop specificity

agranulocytes

monocyte

macrophage

dendritic cells

T cell

B cell

NK cell

NKT cell

Gamma-delta T cell

lymphocytes

T cell

B cell

NK cell

NKT cell

Gamma-delta T cell

Leukocytes

monocyte

macrophage

dendritic cells

T cell

B cell

NK cell

NKT cell

Gamma-delta T cell

neutrophil

basophil

eosinophil

mast cell

non-leukocytes

red blood cell

platelet

monocytes

blood phagocytes that mature into either macrophages or dendritic cells

macrophage

Engulf and digest pathogens, dead cells, and debris through phagocytosis

Present antigens (pieces of pathogens) to T cells to initiate the adaptive immune response

dendritic cells

process foreign matter to present to lymphocytes

T cells

attack infected cells and help activate other immune cells

B cell

release and make antibodies

Natural killer cells

destroy virus-infected and cancer cells

natural killer T cells

T cells that have NK activity

Gamma delta T cells

respond to certain antigens and PAMPS

neutrophils

Most abundant WBC

First responders to infection — they engulf and destroy bacteria

basophils

Release histamine during allergic reactions and inflammation in the blood

eosinophils

Involved in allergic reactions and fighting protozoans and worms

mast cells

Release histamine during allergic reactions and inflammation in the tissue

red blood cells

carry oxygen and carbon dioxide

contain hemoglobin, which binds oxygen

platelets

involved in clotting, inflammation, and killing blood-borne bacteria

mononuclear phagocytic system

network of connective tissue fibers

interconnects nearby cells

meshes w/ connective tissue surrounding organs

passageway between tissues and organs

pathogen recognition in the second line of defense

recognize pathogen associated molecular patterns (PAMPS)

do this using pattern recognition receptors (PRR)

third line of defense in pathogen recognition

B or T cell receptors

able to recognize specific antigens for each pathogen

made up of proteins, sugars, nucleic acids, lipids, and more

PRR

like a toll

recognizes PAMPS

this sets in motion a cascade of events inside the host cell that amplifies the defense response

signs of inflammation

rubor

calor

tumor

dolor

loss of function

rubor

redness caused by increased circulation and vasodilation

calor

warmth from increased blood flow

tumor

swelling from an increase in fluid escaping into tissue

dolor

pain from stimulation of nerve endings

major events of inflammation

1. bacteria gets into a wound, mast cells release chemical mediators and vasoconstriction occurs

2. Blood vessels become leaky so immune cells and proteins can exit into the tissue, bacteria get eaten by the white blood cells

3. a scab, edema, and pus formation occurs

4. inflammation calrms and a scar forms

benefits of edema and chemotaxis

dilutes toxic substances that may have been released

neutrophils actively eat and kill bacteria, dead tissue, and particulate matter

fibrin clot traps microbes to prevent further spreading

pus

liquified cell debris, cells, and bacteria

chemotaxis

WBC’s migrate in response to a specific chemical signal given off at the site of an injury or infection. they remain there to perform general and specific immune functions

diapedesis

movement of white blood cells from the bloodstream into tissues

can occur because WBC’s are very mobile and can change shape

receptors on endothelial cells capture them to assist in their transport

phagocytitic cells

neutrophils (best)

macrophages (meh)

monocytes (worst)

phases of phagocytosis

1. chemotaxis by the phagocyte

2. microbe binds to the PRR on the phagocyte

3. microbes are engulfed into a phagocytic vacuole

4. phagosome forms

5. lysosome binds to the phagosome, forming a phagolysosome

6. lysosome kills the microbe and breaks it down

7. debris is released from the phagocyte by exocytosis

extracellular killing

done by eosinophils

attracted to sites of parasitic infection and antigen-antibody rxns

the worm or protozoa is too big to fit inside the cell so must be killed outside

chronic inflammation

responsible for many chronic and autoimmune diseases

can affect the entire body system (like lungs/skin/joints etc.)

fever

elevated body temp associated with infection or even allergies and some cancers

low grade: 100-101F (endogenous)

moderate: 102-103F

high: 104-106F (exogenous)

pyrogens, exogenous and endogenous

cause the hypothalamus to raise body temperature

exogenous comes from outside the body, like microbes and is an endotoxin

endogenous comes from inside the body like your cells during phagocytosis

benefits of fever

slows down multiplication of temp sensitive microorganisms

reduces availability of iron (essential for bacteria)

increases metabolism and stimulates immune rxns.

speeds up all other immune rxns.

increases availability of certain lymphocytes