Immune SystemImmune System

Means of Defense (3 categories)Means of Defense (3 categories)

First two are First two are Nonspecific Nonspecific

A. BarriersA. Barriers– Doesn’t distinguish between agentsDoesn’t distinguish between agents– Helps Prevent Entry into the bodyHelps Prevent Entry into the body– Includes skin and mucous membranes which provide a Includes skin and mucous membranes which provide a

mechanical and chemical barriermechanical and chemical barrier– Oil and sweat glands give skin an acidic pH which Oil and sweat glands give skin an acidic pH which

discourages bacterial growthdiscourages bacterial growth– Perspiration, tears, and saliva contain an enzyme Perspiration, tears, and saliva contain an enzyme lysozyme lysozyme

whichwhich breaks down the cell walls of bacteria. breaks down the cell walls of bacteria.– Stomach acid kills bacteriaStomach acid kills bacteria– Nostril hairs-filter out particles and mucous traps Nostril hairs-filter out particles and mucous traps

microorganisms. (swept out by cilia)microorganisms. (swept out by cilia)

Means of Defense (3 categories)Means of Defense (3 categories)

B. Nonspecific Internal DefensesB. Nonspecific Internal Defenses– 1. Phagocytic cells like neutrophils and monocytes attack 1. Phagocytic cells like neutrophils and monocytes attack

microorganisms that get through the skin barriers. They microorganisms that get through the skin barriers. They engulf them and consume bacteria, viruses and cell debris in engulf them and consume bacteria, viruses and cell debris in the interstitial fluid.the interstitial fluid.

– Neutrophils make up 60-70% of WBC’s. Short lived.Neutrophils make up 60-70% of WBC’s. Short lived.– Monocytes become macrophages which live a long time.Monocytes become macrophages which live a long time.– Many wander but some are permanent residents in organs like Many wander but some are permanent residents in organs like

the lung or brainthe lung or brain– Can engulf 100+ bacteriaCan engulf 100+ bacteria– 2. Natural Killer Cells2. Natural Killer Cells– Destroy the body’s own infected cells-especially those with Destroy the body’s own infected cells-especially those with

viruses in themviruses in them– Destroys cells which may be changing and could form tumorsDestroys cells which may be changing and could form tumors– Not phagocytic but lytic-breaks cell membranes. Not phagocytic but lytic-breaks cell membranes.

Means of Defense (3 categories)Means of Defense (3 categories)

3. The Inflammatory Response 3. The Inflammatory Response Triggered by damage to tissues by injury or microorganismsTriggered by damage to tissues by injury or microorganismsInjured cells give off a substance that aids the inflammatory Injured cells give off a substance that aids the inflammatory responseresponserelease histamine-which causes dilation of neighboring blood release histamine-which causes dilation of neighboring blood vessels and makes the capillaries more leaky (histamine is vessels and makes the capillaries more leaky (histamine is contained in WBC’s called basophils and in mast cells (in contained in WBC’s called basophils and in mast cells (in connective tissue)connective tissue)Small blood vessels dilate and this increased blood flow causes Small blood vessels dilate and this increased blood flow causes the redness, heat and swelling associated with infection. Blood the redness, heat and swelling associated with infection. Blood vessels also become leakier causing swelling due to increased vessels also become leakier causing swelling due to increased fluid.fluid.The increased blood flow enhances migration of phagocytic The increased blood flow enhances migration of phagocytic WBC’s from the blood to the interstitial fluidWBC’s from the blood to the interstitial fluidneutrophils firstneutrophils firstfollowed by monocytes that develop into macrophagesfollowed by monocytes that develop into macrophages

More Inflammatory ResponseMore Inflammatory Response

Pus- is mostly dead cells and accumulated fluid Pus- is mostly dead cells and accumulated fluid (will be absorbed)(will be absorbed)Clotting proteins in plasma seal the area off and Clotting proteins in plasma seal the area off and prevent the spread of infection.prevent the spread of infection.Systemic ReactionsSystemic Reactions– the number of WBC’s circulating is increased ( may the number of WBC’s circulating is increased ( may

be dramatic and within hours)be dramatic and within hours)feverfevertoxins from the pathogens may trigger fever.toxins from the pathogens may trigger fever.Some WBC’s release pyrogens which set the body Some WBC’s release pyrogens which set the body thermostat higherthermostat higherThe higher temperature stimulates phagocytosis and inhibits The higher temperature stimulates phagocytosis and inhibits the growth of microorganisms and may speed up repair.the growth of microorganisms and may speed up repair.

Still More Non-specific ResponseStill More Non-specific Response

4. Antimicrobial Proteins- Some proteins attack 4. Antimicrobial Proteins- Some proteins attack microorganisms or negatively affect their reproduction.microorganisms or negatively affect their reproduction.

– A. InterferonA. Interferon- a substance produced by a virus infected cell - a substance produced by a virus infected cell that helps other cells resist the virusthat helps other cells resist the virus

– -The virus turns on the interferon gene- can save the infected -The virus turns on the interferon gene- can save the infected cell but diffuses to nearby cells and inhibits viral reproduction cell but diffuses to nearby cells and inhibits viral reproduction therethere

– -Host specific-not virus specific-Host specific-not virus specific– -Inteferon may act against cancer since some may be induced -Inteferon may act against cancer since some may be induced

by virusesby viruses– one kind mobilizes natural killer cells-destroys tumor cellsone kind mobilizes natural killer cells-destroys tumor cells– may change malignant cell membranes- make them less likely may change malignant cell membranes- make them less likely

to metastasizeto metastasize– activates macrophagesactivates macrophages

Another Antimicrobial ProteinAnother Antimicrobial Protein

B. ComplementB. Complement– many (at least 20) proteins that work with other many (at least 20) proteins that work with other

defense mechanismsdefense mechanisms– They circulate in the blood in an inactive formThey circulate in the blood in an inactive form– They are activated by the immune response or They are activated by the immune response or

markers on microorganismsmarkers on microorganisms– They increase the inflammatory response- They increase the inflammatory response-

histamine release and attraction of phagocytes.histamine release and attraction of phagocytes.– They coat microbes- this increases the rate of They coat microbes- this increases the rate of

phagocytosis by opsonization (“making tasty”)phagocytosis by opsonization (“making tasty”)– They team up to cause lysis of the microbial They team up to cause lysis of the microbial

membranemembrane

The Third Line of DefenseThe Third Line of Defense

C. SpecificC. Specific Immune Response Immune Response– The immune system learnsThe immune system learns to distinguish “self” from “non-self”to distinguish “self” from “non-self”– Detects “antigens”- foreign substances . These cause an increase in Detects “antigens”- foreign substances . These cause an increase in

the cells that attack or produce antibodies. They may be things like the cells that attack or produce antibodies. They may be things like molecules on surfaces of viruses and bacteria or marker molecules molecules on surfaces of viruses and bacteria or marker molecules on transplanted organs.on transplanted organs.

– The immune response must be activated by the presence of an The immune response must be activated by the presence of an antigenantigen

– The response is specific for a particular foreign substance or invaderThe response is specific for a particular foreign substance or invader– The system remembers the antigens after the initial contact. There is The system remembers the antigens after the initial contact. There is

a quick response the second time. This is memory.a quick response the second time. This is memory.– Vaccination- immune response is prevented with a nonvirulent or Vaccination- immune response is prevented with a nonvirulent or

weakened form of a pathogen-initiates long term capability to respond weakened form of a pathogen-initiates long term capability to respond quickly to real infective agent.quickly to real infective agent.

– -Active immunity- body produces antibodies-Active immunity- body produces antibodies– -Passive immunity- body acquires antibodies from other sources such -Passive immunity- body acquires antibodies from other sources such

as placenta, injection, immunity is temporaryas placenta, injection, immunity is temporary