Download cells - Pomp

The Immune System
• Chapter 43 ~
Lines of Defense
Nonspecific Defense Mechanisms……
PCA:
• List the organs involved in the immune sytem:
Innate Immunity:
• Specialized phagocytic white blood cells
• Antimicrobial proteins
• Inflammatory response
Innate Immunity: 5 types of Leukocytes
• Neutrophils
• 60-70% WBCs; engulf and
destroy microbes at infected
tissue
Short lived
• Monocytes
• 5% WBCs; develop into….
• Macrophages
1)phagocytosis
• 2)lysosomal enzymes
destroy microbes
• Dendritic cells:
• Stimulate development of
the acquired immune system
Innate Immunity: 5 types of Leukocytes
• Eosinophils
• 1.5% WBCs; destroy large
parasitic invaders
• Enzymatic action- no
phagocytosis
• Natural killer (NK) cells
• destroy virus-infected body
cells & abnormal cells
• apoptosis
Antimicrobial Proteins:
1. Complement system- group of 30 proteins
 Once activated can cause invading cells to
lyse – burst
2. Interferons (α, β and γ)
 Immune response to viruses
 Activates macrophages
The Inflammatory Response
•
Tissue injury; release of chemical signals~
• histamine (basophils/mast cells): causes Step 2...
• prostaglandins: increases blood flow & vessel permeability
• Dilation and increased permeability of capillary~
• chemokines: secreted by blood vessel endothelial cells
mediates phagocytotic migration of WBCs
• Phagocytosis of pathogens~
• fever: leukocyte-released molecules increase body
temperature
Acquired Immunity:
• Lymphocyctes
•pluripotent stem cells...
• B Cells (bone marrow)
• T Cells (thymus)
• Antigen: a foreign molecule that
elicits a response by lymphocytes
(virus, bacteria, fungus, protozoa,
parasitic worms)
• Antibodies: antigen-binding
immunoglobulin, produced by B
cells
• Antigen receptors: plasma
membrane receptors on B and T
cells
Acquired Immunity:
•Epitope- antigenic determinant
• Small area on antigen recognize by lymphcyte
T cell receptors and MHC:
• Major Histocompatibility Complex (MHC)
• Antigen presentation- bind to fragments and bring
them towards the cell surface
• Two classes:
• Class I MHC
• Class II MHC
MHC
• Class I MHC(nucleated body cells): recognizes
antigen fragments in the cell, binds to them
and displays them at the cell surface
– Cytotoxic T cells will bind and destroy fragments
• Class II MHC: recognizes antigen fragments in
the cell, binds to them and displays them at the
cell surface
– Helper T cells will bind and initiate a process to
destroy fragments
Cytotoxic T cell mechanism
• Destroy cells infected by intracellular
pathogens and cancer cells
• Activity enhanced by CD8 surface protein
present on most cytotoxic T cells (similar to
CD4 and class II MHC)
• cell lysis and pathogen exposure to circulating
antibodies
Cytotoxic T cell mechanism:
• the activated cytotoxic T cells release:
– perforins which form pores in the target cell
membrane
– and proteolytic enzymes which enter the cell via
endocytosis and initiate apoptosis
• Cytotoxic T cell becomes first activated by the secretion of
cytokines from helper T cells
Cytotoxic T cell mechanism
Helper T cell mechanism:
• Function in both humoral & cell-mediated
immunity
• Stimulated by antigen presenting cells
• T cell surface protein CD4 enhances
activation(similar to CD8 of class II MHC)
• Cytokines secreted (stimulate other lymphocytes):
• a) interleukin-2 (IL-2): activates B cells and cytotoxic T cells
• b) interleukin-1 (IL-1): activates helper T cell to produce IL-2
Helper T cell mechanism:
• a helper T cell recognizes the complex
becomes activated with the aid of cytokines
secreted by the macrophage forming a clone of
activated helper T cells
• an activated T cell binds to the B cell
• B cell becomes activated with the help of
cytokines
Helper T cell mechanism
Clonal Selection:
• 1. antigen binds to antigen receptors of a specific
lymphocyte
• 2. the selected lymphocyte proliferates forming a
clone of identical cells bearing the same receptors
• 3. some of the proliferated cells develop into shortlived effector cell(plasma cell if B lymphocyte,
helper T cell or cytotoxic T cell if T lymphocyte) that
secrete antibodies specific for the antigen or destroy
the antigen
• 4. some proliferated cells develop into long lived
memory cells that can respond rapidly upon exposure
of the same antigen
Clonal Selection
Induction of Immune Responses
•primary immune response- the selective
proliferation and differentiation of lymphocytes
that occur the first time the body is exposed to a
particular antigen (10-17 days)
•secondary immune response- if individual is
exposed again to the same antigen, the response
is faster( 2- 7 days)- immunological memory
Induction of Immune Responses
Types of immune responses
•
•
•
•
Humoral immunity
B cell activation
Production of antibodies
Defend against bacteria,
toxins, and viruses free
in the lymph and blood
plasma
• Cell-mediated immunity
• T cell activation
• Binds to and/or lyses
cells
• Defend against
intracellular pathogens
such as bacteria,
viruses, fungi, protozoa,
and parasite s; and
cancer cells
Humoral response: B cells
• Stimulated by T-dependent
antigens (help from TH cells)
• Macrophage (APCs) with class II
MHC proteins
• Helper T cell (CD4 protein)
• Activated T cell secretes IL-2
(cytokines) that activate B cell
• B cell differentiates into memory
and plasma cells (antibodies)
Antibody Structure & Function
• Epitope: region on antigen surface recognized by antibodies
• 2 heavy chains and 2 light chains joined by disulfide bridges
• Antigen-binding site (variable region)
5 classes of Immunoglobins
•
•
•
•
•
IgM: 1st to circulate; indicates infection;
too large to cross placenta
IgG: most abundant; crosses walls of blood
vessels and placenta; protects against
bacteria, viruses, & toxins; activates
complement
IgA: produced by cells in mucous
membranes; prevent attachment of
viruses/bacteria to epithelial surfaces; also
found in saliva, tears, and perspiration
IgD: do not activate complement and
cannot cross placenta; found on surfaces of
B cells; probably help differentiation of B
cells into plasma and memory cells
IgE: very large; small quantity; releases
histamines-allergic reaction
Antibody-mediated Antigen Disposal
• Opsonization: antibody binds to and blocks antigen
activity-coats antigen surface enhancing
macrophage activity
• Agglutination: antigen clumping- antibodies
contain at least two antigen binding sites
• Precipitation: cross-linking of soluble antigensforms immobile aggregates that are disposed of by
phagocytosis
• Viral Neutralization: antibodies bind to certain
proteins on the surface of a virus blocking its
ability to infect a host cell
Immunity in Health & Disease
• Active immunity
• natural: conferred
immunity by recovering
from disease
• Active immunity
• artificial: immunization
and vaccination;
produces a primary
response
• Passive immunity: transfer
of immunity from one
individual to another
• natural: mother to fetus;
breast milk
• artificial: rabies
• Transfer of antibodies from
rabid(immune) animal to
non-rabid (non-immune)
animal
Self/Nonself Recognition
• Self-tolerance: capacity to distinguish self from
non-self
• Autoimmune diseases: failure of self-tolerance;
multiple sclerosis, lupus, rheumatoid arthritis,
insulin-dependent diabetes mellitus
Blood Group and Transfusions:
• See PCA: Explain why blood type AB is
considered the universal recipient and
blood type O is considered the universal
donor?
Abnormal immune function
• Allergies (anaphylactic shock): hypersensitive
responses to environmental antigens (allergens);
causes dilation and blood vessel permeability
• Allergy symptoms can be diminished with
antihistamines
– The hormone epinephrine counter acts this allergic reaction
• Autoimmune disease:
• Immunodeficiency disease: SCIDS (bubble-boy);
A.I.D.S.
Essay: 10pts.
• 1. Describe the main role of the following
cells types: helper T cells, cytotoxic T cells
and B cells.
• 2. What is responsible for the activation of
these molecules?
• 3. What deficiencies, if any would result from
an individual born without a Thymus?