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Immune System
Chapter 43
2 Types of Immunity
 2 major kinds of defenses have evolved to counter
threats of viruses, bacteria, & other pathogens
 Innate Immunity
 Present PRIOR to exposure
 Effective from time of birth
 Nonspecific
 Acquired Immunity
 Present only AFTER exposure
 Highly specific
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Innate Immunity
 Barrier Defenses
 Cellular Innate Defenses
 Inflammatory Response
 Natural Killer (NK) Cells
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Barrier Defenses
 Skin
 Provides physical barrier to pathogens
 Mucous membranes that cover epithelial linings and
surfaces
 Physical barrier as well
 Secretions that lower skin pH
 Lysozymes
 Found in tears, sweat, & mucous secretions
 Digests bacterial cell walls
 Especially effective in eyes & Upper Resp. Tract (URT)
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Cellular Innate Defenses
1. Phagocytic White Blood Cells (WBC) or
Leukocytes
 Neutrophils
 Leukocytes that ingest + destroy microbes
(phagocytosis)
 Most abundant leukocyte
 Chemotaxis attracts neutrophils to infected
cells
 http://en.wikipedia.org/wiki/File:S15Competitive_Phagocytosis_Assay_in_Collage
n.ogg
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Cellular Innate Defenses (Page 2)
 Eosinophils
 Leukocytes that discharge hydrolytic
enzymes when in close proximity to
parasites (eukaryotic organisms)
 Monocytes
 Phagocytic leukocytes that develop into
macrophages
 Macrophages are giant phagocytic cells
Monocyte
 Stimulate other immune responses
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Summary of Phagocytic WBCs
 IF a microbe gets past the barriers, phagocytosis may
occur
 Ingestion of invading microbes by WBCs called phagocytes
 Neutrophils
 WBCs that ingest & destroy microbes by phagocytosis
 Monocytes
 Develop into macrophages (giant phagocytic cells)
 Eosinophils
 Leukocytes that defend against parasitic invaders by
secreting hydrolytic enzymes on them
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Cellular Innate Defenses (Page 3)
2. Antimicrobial Proteins
 Interferon
 Innate defense against viral
infections
 Alter cells adjacent to viralinfected cells to produce
substances that inhibit viral
replication
 Complement System
 Leads to the lysis of invading cells
 Also play a role in inflammation &
acquired defense
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Inflammatory Response
 Tissue damage due to physical injury (trauma) or
pathogen entry
 This triggers the release of chemical signals which result
in an inflammatory response
 Histamine – chemical released in response to injury
 Stored in Mast Cells (mastocyte) (found in connective tissues)
 Trigger the dilation and permeability of nearby capillaries
 Delivers clotting agents & phagocytic cells to the injured area
 Fever & septic shock
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 http://video.google.com/videosearch?sourceid=chrom
e&q=inflammatory+response&um=1&ie=UTF8&ei=OweUS6ChJoS0tgfrhsTUCg&sa=X&oi=video_resul
t_group&ct=title&resnum=10&ved=0CDAQqwQwCQ#
 Videos 2 & 4
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1. Chemical signals (like histamines) released by macrophages & mast cells at
the injury site
2. Nearby capillaries dilate & become more permeable
3. Clotting begins
4. Chemokines attract more phagocytic cells from the blood to the injury site
5. Neutrophils & macrophages phagocytose pathogens & cell debris
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-itis = Inflammatory Response
 Appendix  appendicitis
 Pancreas  pancreatitis
 Meninges  meningitis
 Liver  hepatitis
 Joints  arthritis
 Septic shock – overwhelming inflammatory response
(systemic)

High fever + Low BP
 Most common cause of death in critical care units (CCUs)
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Natural Killer (NK) Cells
 4th type of innate immunity
 Patrol the body and attack virus-
infected body cells
 Also attack cancerous cells
 Recognize & remove diseased cells
 NK releases chemicals that lead to
apoptosis
 Apoptosis = programmed cell death
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Acquired Immunity
 Lymphocytes provide SPECIFIC defenses
 2nd line of defense
 2 Types of Lymphocytes (NOT Leukocytes (WBCs))
 B Lymphocytes – B Cells
 Proliferate in Bone marrow
 Produce antibodies
 T Lymphocytes- T Cells
 Mature in the Thymus
 Helper T-cells (CD4) or Cytotoxic T-cells (CD8)
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Acquired Immunity (Page 2)
 Lymphocytes circulate through the blood and lymph
 Lymphocytes are concentrated in the spleen, lymph
nodes, & other lymphatic tissues
 Recognize antigens by antigen-specific receptors on their
plasma membranes
 Antigen – any foreign molecule that elicits a response by
lymphocytes
 A lymphocyte may have 100,000 receptors, but all of them
are specific for only 1 epitope
 Epitope – small accessible part of an antigen
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Antibodies
 Produced by B-cells
 When secreted, the antibodies are called
immunoglobulins
 Part of the humoral immune response
 Specific to a given antigen
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Epitopes
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Activation
 Either B- or T-cells can be activated
 Occurs when an antigen binds to a B or T cell
 Activation leads to each lymphocyte forming 2 types of
clonal cells
 Clonal cells are all specific to the antigen
 1. Effector cells – combat the antigen
 2. Memory cells – Long-lived & bear receptors for the same
antigen
 Allows for a quick immune response in the FUTURE
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How do B-cells and T-cells Differ?
 B-cell receptors bind intact antigens
 T-cells bind antigens presented to them by antigen-
presenting cells (APC)
 B-cell or T-cell responds to only ONE antigen (Specific)
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MHC Proteins
 Immune system’s way of recognizing “self” cells
 Major Histocompatibility Complex molecules (MHC)
 Every individual is different in their MHC proteins
 MHC proteins bind to an antigen and bring it to the cell
surface
 Called antigen presentation
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MHC Proteins (Page 2)
 Two types of MHC proteins
 Class 1 MHC – All cells but RBCs
 Recognized by cytotoxic T-cells (CD8)
 Class 2 MHC – B cells & macrophages
 The B cells and macrophages that use Class 2 MHC proteins
are called APC (Antigen-presenting cells)
 Associated with Helper T-cells (CD4)
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Immune Response Types
 Primary Immune Response
 First exposure to an antigen
 Lymphocyte activation
 Secondary Immune Response
 Antigen in encountered again
 Rapid & stronger response
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Acquired Immunity
 Humoral Immune Response
 Involves the activation and clonal selection of effector B cells
 B cells produce antibodies that circulate in the blood
 Helper T-cells are also involved in the activation of B cells
 Cell-Mediated Immune Response
 Activation and clonal selection of cytotoxic T cells
 Cytotoxic T cells identify & destroy infected cells
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Notes on Acquired Immunity
 Helper T cell (CD4)
 Aids in BOTH responses
 Class II MHC on an APC activates the Helper T cells
 Secrete cytokines which stimulate BOTH Cytotoxic-T-cells
and B-cells
 CD4 protein holds helper T-cell to class II MHC
 Cytotoxic T cell (CD8)
 Binds to Class I MHC
 Bound together by the CD8 protein
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Comparision
 B-cells - produce antibodies (provides humoral immunity)
 B-cells produce memory cells and plasma cells
 Plasma cells secrete antibodies in huge numbers
 Antibodies circulate in blood, then bind & destroy antigen
 Cytotoxic T-cells – destroy infected body cells
 Helper T-cells – activate both B and T cells
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Antibody Actions
 Neutralization – Antibodies bind to pathogen’s surface
proteins
 Prevents pathogen from entering & infecting cells
 Opsonization
 Results in increased phagocytosis of the antigen
 Lysis
 Caused by activation of the complement system
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Immunities
 Active Immunity
 Body comes in contact with antigens
 Actively produces antibodies in response to antigen
presentation
 Naturally developed immunity after an infection
 Vaccination or immunization
 Passive Immunity
 Individual receives antibodies
 Placental transmission of immunoglobulins (Antibodies)
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Show vaccination video
 Vaccination Video
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Erythrocyte (RBC) Antigens
 A, B, AB, or none
 Determined by antigen presence on RBC surface
 IF non-self, antibodies will form on the foreign antigens
 Destroy transfused RBCs
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Immune System Pathologies
 Lupus, Rheumatoid arthritis, and MS
 Immune system fails to recognize body cells
 Since these cells are detected as foreign, immune system
attacks the body’s own healthy cells
 HIV – attacks CD4 cells or Helper-T-cells
 Allergies – body over-responds to an allergen
 IgE – immunoglobulin E
 Histamine & other mediators cause vasodilation and other
symptoms
 Mast cells mediate the histamine production
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