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Immune System
Chapter 43
Introduction to the Immune System
The human body must defend itself against
unwelcome intruders.
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It must also deal with abnormal body cells,
which, in some cases, may develop into
cancer.
Two major kinds of defense have evolved to
counter such threats.
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Innate Defenses
Acquired Defenses
Overview of the Immune System
External Barriers:
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intact skin epidermis
Acid mantle of skin
Keratin
Intact mucous membranes
Mucus
Nasal hairs
Cilia
Gastric juice
Acid mantle of vagina
Lacrimal secretion
Urine
Oil (sebum) secretions
Internal Cellular Defenses:
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Phagocytic cells
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Neutrophils
Monocytes
Eosinophils
Dendritic cells
Internal Cellular Defenses
Phagocytic Responses
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Pseudopodia
Ingestion
Vacuole
Fuse with lysosome
Digestion
Exocytosis
Internal Cellular Defenses:
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Natural Killer Cells
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Non-specific
Perforins
Apoptosis
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Natural Killer (NK) Cells (Cytotoxic
lymphocyte)
Promote cells lysis by direct cell attack against
virus-infected or cancerous body cells
Referred to as null third population cells that are
spontaneous non antigen recognizing.
Lack surface antigen receptors but recognize
certain surface sugars on infected or cancerous
cells
Release cytolytic chemicals (perforins) that
attack a targets cell's cell membrane and bore
hole. Granzymes are released and cellular
enzymes disrupted.
Present in spleen, lymph nodes, red bone
marrow, and blood
Inflammatory Response
Inflammatory Response
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Cardinal signs of
inflammation
redness, pain, heat
and swelling
Local versus
systemic
inflammation
Septic shock
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Interferons - proteins that diffuse to nearby cells,
where they stimulate the synthesis of a protein known
as PKE, which then interferes with viral replication in
those cells by blocking protein synthesis at the
ribosomes
 Gamma interferon - produced by lymphocytes,
mobilizes and activates macrophages and NK cells,
stimulates synthesis and expression of more class I
and II MHC, and enhances activity of B cells and
cytotoxic T cells
 Alpha interferon - produced by most leukocytes,
mobilizes and activates macrophages and NK cells
 Beta interferon - produced by fibroblasts, mobilizes
and activates macrophages and acts to reduce
inflammation
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Complement - twenty plasma proteins
that amplify the inflammatory response,
lyses microorganisms and enhances
phagocytosis by opsonization. Two
pathways: classic and alternative.
Pyrogens - secreted by macrophages and
signal the body to increase temperature;
high body temperature inhibits microbial
multiplication and enhances body repair
processes.
Antigen (Ags)
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Antigens are substances that can mobilize
immune system and provoke a response
Are considered nonself
ii. Nonself Antigens
Types:
 Complete antigen - functional properties:
 immunogenecity - stimulate B and T cell
formation and antibody production
 reactivity - react with B and T cells
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Small antigens (peptide, nucleotide, hormones) - may
bind to body's own biological molecules (proteins);
antigen when bound to body's own molecules may cause
an immune response, this is called an allergy. Small
antigens are called haptens (incomplete antigen) and
alone are not immunogenic.
Reactivity (immune response) is dependent upon antigen
structure; localized regions, antigenic determinants
are where antibodies or B and T lymphocytes can bind.
iii. Self Antigens
Are not foreign or antigenic to us, but are strongly
antigenic to other individuals
egs. blood transfusions and organ transplants
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Major Histocompatibility Complex (MHC) antigens
Found on all cells except RBCs
Involved in tissue recognition (aids in transplantation
recognition)
Two types of MHC antigens: MHC class I found on all
body cells
MHC class II found on antigen present cells
Antigen Presentation Ingestion of the antigen
Digestion of antigen into peptide fragments
Fusion of vesicles (peptide fragments with MHC-II
molecules)
Binding of peptide fragments to MHC-II molecules
Insertion of antigen-MHC-II complex into plasma
membrane
ACQUIRED IMMUNITY
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All cells have cell
surface
macromolecules
Adaptive immunity is
sensitive to specific
infections
Antigens distinguish
self versus non-self
ACQUIRED IMMUNITY
ACQUIRED IMMUNITY
Humoral Immunity
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Also known as
antibody-mediated
immunity
Utilizes B-lymphocytes
Recognizes antigen
directly
Made in the bone
marrow
Clonal Selection and Proliferation
Antibody Structure
Antibody Classes
Antibody Classes
Antibody Functions
Cell-Mediated Immunity
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Utilizes T-lymphocytes
T-cells are made in
the bone marrow but
mature in the thymus
gland.
Cannot recognize
antigens directly
Cell-Mediated Immunity
CLASS I MHC PROTEIN
CLASS II MHC PROTEIN
Helper T-Lymphocyte Stimulation
Helper T-cells stimulate B-cells
Cytotoxic T-Lymphocyte Stimulation
Overview of Adaptive Immunity
Adaptive Immunity
Problems with the Immune System
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Blood Transfusion Reaction
Tissue Rejection
Allergies
Autoimmune disease
Immunodeficiencies
Blood Transfusion Reactions
Rhesus Factor
Blood Type Presence of Type of
Receive?
D Antigen? Antibody?
Rh Positive
Yes
None
+ and -
No
Anti-D
- only
Rh Negative
Tissue Transplant and Rejection
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Autograft
Isograft
Allograft
Xenograft
Allergies or Hypersensitivities
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Type I
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Type II
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Type III
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Type IV
Autoimmune Diseases
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Multiple sclerosis
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Rheumatoid arthritis
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Systemic lupus
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Grave's disease
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Type I diabetes
mellitus
Immunodeficiency Diseases
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Primary
Immunodeficiency
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a.k.a. “inborn”
SCID
Secondary
Immunodeficiency
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a.k.a. “acquired”
Drugs
Stress and Hodgkin’s
AIDS