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Immune System and
Disease
Chapter 35
Nonspecific Defenses
 The human body faces against many dangerous enemies
 Harmful bacteria, viruses, fungi, and protists
 Pathogens:

Disease causing agents
First line of Nonspecific Defense
 Body’s surface defenses are nonspecific
 Skin is an impenetrable barrier to invading pathogens

Oil and sweat inhibit the growth of pathogens.

Sweat has an enzyme called lysozyme that digests bacterial
walls and kills the bacteria.
 Body’s internal surface uses
 Mucous Membranes

Layers of epithelial tissue that produce a sticky, viscous fluid

Lines nasal passages, lungs, respiratory passages, and
reproductive tract
Second Line of Nonspecific
Defense
 Injury or local infection like a cut can cause and
 Inflammatory Response:

Series of events that suppress infection and speed recovery
 Histamine:

Causes local blood vessels to dilate, increasing blood flow to the area.
 Temperature Response
 Fever

Temperature rises to fight against invading pathogens

Higher temperatures are harmful to many bacterial pathogens

Over 103° can destroy body’s cellular processes (destroy enzymes

Over 105° can be fatal

Destroys cells
Second Line of
Nonspecific Defense Cont.
 Proteins

Complement System:


20 different proteins which circulate in the blood and become active when they
encounter pathogens
Interferon:

A protein released by cells infected with viruses

Cause nearby cells to produce an enzyme that prevents viruses from making
proteins and RNA.
 White Blood Cells

Neutrophils:


Macrophages:


WBC that engulfs and destroys pathogens
Ingest and kill pathogens they encounter
Natural Killer cells:

Large WBC that attacks cells infected with pathogens
Cells Involved
 The third line of defenses is specific
 4 Main kinds of WBC’s that participate in the immune
response
 Macrophages
 Cytotoxic T cells:

Attack and kill infected cells
 B cells:

Label invaders for later destruction by macrophages
 Helper T cells:

Activate both T and B cells
Recognizing Invaders
 An infected body cell will display antigens of an invader
on its surface
 Antigen: Substance that triggers an immune response.
Immune Response Parts
 B cell response is a
passive defense that
aids in the removal of
pathogens.
 T cell response is an
active cell-mediated
defense that involves
the destruction of
pathogens by cytotoxic
T cells.
Steps of an Immune
Response
 When a virus infects a cell, the cell displays viral antigens on its
surface.
 Macrophages engulf and destroy viruses and also display viral
antigens.
 Helper T cells bind to antigens on the macrophages and they
(macro) release interleukins.
 Interleukins make Helper T cells activate Cytotoxic T and B
cells.
Steps Continued
 B cells divide and turn into plasma cells
 Plasma cells make antibodies that bind to viral parts
and to infected cells and mark them for death.
 Macrophages engulf and destroy the “marked” viral
parts and infected cells.
 Cytotoxic T cells also destroy infected cells that are
marked.
 Some B cells become memory cells that will
immediately destroy the virus if it tries to invade the
body again.
Disease Transmission and
Prevention
 Diseases are transmitted in 5 different ways
 Person to person contact
 Air
 Food
 Water
 Animal bites
Detecting Disease
 German physician Robert Koch established a procedure
for diagnosing causes of infection
 Koch’s Postulates:

Guide for identifying specific pathogens

4-step procedure

1. The bacteria must be present in every case of the disease.

2. The bacteria must be isolated from the host with the
disease and grown in pure culture.

3. The specific disease must be reproduced when a pure
culture of the bacteria is inoculated into a healthy
susceptible host.

4. The bacteria must be recoverable from the experimentally
infected host.
Resistance to Disease
 Immunity:
 Resistance to a particular disease
 Vaccination:
 Medical procedure used to produce immunity
 Vaccine:

A solution that contains a dead or modified pathogen that can
no longer cause disease
 Antigen Shifting:
 Subsequent exposure to a virus causes the body to make
new antibodies.
Disorders of the Immune
System
 In some people, the immune system can not distinguish
between the body’s antigens and foreign antigens.
 Autoimmune disease:
 The body launches an immune response against its own
cells, attacking body cells as if they were pathogens.
 Examples:

Graves Disease

Multiple Sclerosis

Type 1 Diabetes
HIV and AIDS
 HIV, the virus that causes AIDS, infects helper-T
cells
 HIV: Human immunodeficiency virus
 AIDS: Acquired immunodeficiency syndrome
 HIV is contracted through sexual contact, blood
transfusions, and contaminated needles (drug
users, tattoos, piercing)
 HIV infects cells by using proteins on its surface
attach to the host cell (helper-T cells)
 The HIV virus infects only a few cells at time, so
it takes a long time to show symptoms.