THE IMMUNE STYSTEM

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The Immune System

The body must defend itself against potentially dangerous viruses, bacteria and other pathogens. It must also contend with abnormal cells and cell that may develop into cancer.

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Cancer cells in bone marrow

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HIV

The Immune System

There are two types of defense that the body has to fight these threats. Innate Immunity – a defense that is present

from birth. Usually nonspecific responding to a broad range of microbes. Consists of external and internal barriers, phagocytic white blood cells called macrophages.

Acquired Immunity – also called adaptive immunity. Developes only after exposure to microbes, abnormal body cells, and toxins. Highly specific. White blood cells called lymphocytes are involved as well as proteins called antibodies.

Overview of defenses against bacteria viruses and other pathogens

INNATE IMMUNITYRapid Responses to a

broad range of microbes

ACQUIRED IMMUNITYSlower responses to

specific microbes

External defenses Internal defenses

Skin Mucous membranes Secretions 1st line of defense

Phagocytic Cells Antimicrobial proteins Inflammatory Response Natural Killer Cells 2nd line of defense

Humoral Response(antibodies) Cell Mediated response

(Cytotoxic lymphocytes) 3rd line of defense

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Flu Virus

External Defenses:

These are the first line of defense from diseases

Skin

is impenetrable to viruses or bacteria.

Tiny cuts may allow penetration of pathogens. QuickTime™ and a

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Mucous membranes

line the respiratory, digestive and genitouterary tracts block entry of pathogens. Cells of these membranes produce mucus which traps microbes.

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Ex: The trachea has ciliated epithelial cells that sweep mucus and any trapped debris upward away from the lungs.

Secretions

Saliva, tears - wash away surfaces of epithelial cells.

Sebaceous (Oil) glands and sweat glands - give the skin a pH ranging from 3 -5 which is acidic enough to prevent the colonization of some microbes

Lysozyme – an enzyme contained in secretions from the skin that digests the cell walls of many bacteria (peptidoglycan)

Gastric Juices – acidic pH kills pathogens before they reach the intestines.

Exception: Hepatitis A virus can survive gastric acidity

Internal Defenses – 2nd Line

microbes that get past the external defenses must then contend with the internal mechanisms of innate defense.

Phagocytic Cells

phagocytosis is the ingestion of invading microorganisms by a certain type of wbc called phagocytes.

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Attach to their prey by way of surface receptors that bind to structures found on many microbes but not on regular body cells. An example of this structure is polysaccharides found on the surface of bacteria.

Engulfs the microbe(s) then forms a vacuole. Vacuole fuses with a lysosome Nitric oxide and other toxins poison the

microbes Enzymes breakdown the molecules that make

up the microbe

4 Types of White Blood Cells (leukocytes) that are phagocytic:

Neutrophils Enter infected tissue and engulf microbes

about 70% of wbc’s. Self destruct in a few days

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Macrophages“the big eater” large phagocytes that engulf microbes and dead tissue cells. Live longer than neutrophils

Eosinophils Attack large parasites with enzymes (blood fluke)

Dendritic Cells Ingest microbes like macrophages and

stimulates acquired immunity

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Antimicrobial proteins – proteins that become activated and secreted when there is an infection.

Examples include lactoferrin binds iron which is necessary for bacteria to grow and defensins which kill fungi

bacteria and viruses

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Complement System - a group of proteins that lead to the lyses (bursting) of invading microbes. Substances on the surface of microbes

activate the complement system.

Interferons

Limit the spread of viruses by keeping them from replicating.

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Inflammatory Response

Damage to tissue by physical injury or entry of pthogens leads to the release of chemical signals that trigger a response.

Histamine - a chemical stored in mast cells found in connective tissues. Histamine dilates capillaries and increases their permeability

Chemokines are small proteins that guide phagocytes to the site of injury

Macrophages release chemicals like prostoglandins that promote blood flow to the site of injury

Result is inflammation, redness, swelling.

Natural Killer Cells

NK cells patrol the body and attack viral infected cells and cancer cells

Once attached to an infected cell, it releases chemicals that cause the cell to undergo apoptosis (programmed cell death)

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