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Chapter 43: The Body’s Defenses
Lines of Defense
First Line – Nonspecific
 Skin
 Mucous
Second Line – Nonspecific
 Phagocytic White Blood Cells (WBC)
 Inflammatory Response
 Antimicrobial Proteins
Third Line – Specific
 Lymphocytes
 Antibodies
First Line
Skin and Mucous
 Intact skin usually cannot be penetrated by microorganism
 Mucous Membrane
o Digestive Tract, Respiratory Tract, Genitourinary Tract
 Chemical Defenses
o Low pH in sweat and stomach
o Washing by tears and saliva
Second Line
Nonspecific
White Blood Cells
 Phagocytosis – ingesting of invading organisms
 Neutrophils
o Chemotaxis – migration toward chemical attractant
 Monocytes
o Form macrophages, “big eaters”
 Eosinophils
o Take care of larger parasitic invaders
 Natural Killer (NK) cells
o Attack cell’s membrane causing it to lyse (burst open)
Antimicrobial Proteins
 Attack microbes directly or impede reproduction
 Complement System – set of 20 serum proteins that carry out a cascade of steps leading to the
lysis of microbes
 Interferon
o Secreted by virus infected cells
o Induce neighboring cells to produce chemical that inhibit viral reproduction
Inflammatory Response
 Triggered by damage to tissue by physical injury or entry of microorganism
 Precapillary arterioles dilate and postcapillary venules constrict to increase blood supply
 Full capillaries leak fluid into near tissue to cause edema(swelling)
 Inflammatory response initiated by chemical signal
o Histamine – release by cells of body, the basophils and mast cells
o Basophils – circulating white blood cells
o Mast cells – in connective tissue
 Soon phagocytic migration begins and is mediated by chemotactic factors called chemokines
Pyrogens are released and set body’s temperature higher causing fever
Third Line
Specific
Two main types of lymphocytes
• B lymphocytes (B Cells)
• T lymphocytes (T Cells)
 B Cells combat antigens by secreting receptors called antibodies
 T Cells have special receptors called T Cell Receptors that is not secreted
Lymphocytes
• Key to the immune system
• Migrate from bone marrow
• The different lymphocytes specialize in different types of antigens and respond accordingly
• Antigen – foreign molecule that elicits a response from lymphocytes
When Lymphocytes are activated they divide and differentiate into two clones of cells (Clonal Selection)
• Effector cells, short lived clones that combat the same antigen that activated
• Memory cells, long lived cells that have receptors for the same antigen
Primary Immune Response – when lymphocytes are activated upon first exposure to antigen
Secondary Immune Response - If the same antigen comes at a later time. Response is faster,
greater magnitude, and more prolonged
Lymphocyte development gives rise to an immune system that distinguishes self from nonself
Lymphocytes that have receptors for molecules in the body exhibit apoptosis
• Leaves only one that react with foreign molecules
T Cells interact with group of native molecules called Major Histocompatibility Complex(MHC)
• Each MHC presents fragments of protein antigen to a T Cell
• Two main classes of MHC
Class I MHC – found all nucleated cells
Class II MHC – few specialized cell types
T Cells
Cytotoxic T Cells (Tc) have antigen receptors that bind to fragments of antigens displayed by the body’s
class 1 MHC molecules
Helper T Cell (TH) have receptors that bind to fragments of antigens displayed by the body’s class 2 MHC
molecules
Suppressor T Cell (TS) function in turning off the immune response once antigen has been eliminated
from body
Immune System
Humoral Immunity
• Have receptors that bind to fragments of antigens displayed by the body’s class 2 MHC molecules
• Defends against free bacteria, toxins, and viruses present in body fluids
• The repeated subunits of these antigens bind simultaneously to a number of membrane antibodies
on the B cell surface
Cell-mediated immunity
• Active against bacteria and viruses within infected body cells and against fungi, protozoa, and
parasitic worms
• It kills target cell primarily by releasing perforin, a protein that forms pores in the target cell’s
membrane
• As water flows into the target cell it swells and eventually lyses
Antibodies
An antibody interacts with a small accessible portion of the antigen called an epitope or antigenic
determinant
Antibodies constitute a group of globular serum proteins called immuniglobulings
The secreted antibodies bind to antigen
Typical antibody molecule has:
• 2 identical antigen binding sites specific for
• 2 identical light chains
the epitope that provoked its production
• Joined by disulfide bridges to form a Yshaped molecule
• 4 polypeptide chains
• 2 identical heavy chains
Opsonization, the bound antibodies enhance macrophage attachment to and thus phagocytosis of the
microbes
Immunity
Active immunity
• Immunity conferred by recovering from
• Can be by immunization (vaccination)
an infectious disease
Passive immunity
• Antibodies can be transferred from one
• Can be transferred by injecting
individual to another(mother to nursing
antibodies from animal that is already
infant in breast milk)
immune to another
• Passive immunity persists only as long
as antibodies last
Autoimmune and Immunodeficiency Disease
Autoimmune
• Immune system looses tolerance for self and turns against certain molecules of the body
Immunodeficiency
• Severe combined immunodeficiency- both branches of immune system fail to function