The Immune System
Ch43
Tori-Section 1, Julia- Section 2, RyleeSection 3 & 4
43.1 In innate immunity, recognition
and response rely on traits common
to groups of pathogens
Innate immunity- a defense that is active immediately upon
infection and is the same whether or not the pathogen has
been encountered previously.
Adaptive immunity- a defense found only in vertebrates,
they produce a vast arsenal of receptors, each of which
recognizes a feature typically found only on a particular
part of a particular molecule in a particular pathogen.
Innate Immunity of Invertebrates
● In vertebrates, intact skin and mucous membranes form
barriers to pathogens
● Mucus produced by membrane cells, the low pH of the
skin and stomach, and degradation by lysozymes also
deter pathogens.
● Microbes that penetrate barrier defenses are ingested by
phagocytic cells, including macrophages and dendritic
cells.
Innate Immunity of Vertebrates
•The immune system of mammals is the best
understood of the vertebrates
•Innate defenses include barrier defenses,
phagocytosis, antimicrobial peptides
•Additional defenses are unique to vertebrates:
natural killer cells, interferons, and the
inflammatory response
phagocytosis
When any pathogen breaches an insects barrier
defenses encounter a number of internal immune
defense. Immune cells called hemocytes travel
throughout the body in the hemolymph.
● Some of those hemocytes carry out a defense called
phagocytosis
● There are different types of phagocytic cells
–Neutrophils engulf and destroy pathogens
–Macrophages are found throughout the body
–Dendritic cells stimulate development of adaptive
immunity
●
phagocytosis
Barrier Defenses
•Barrier defenses include the skin and mucous
membranes of the respiratory, urinary, and
reproductive tracts
•Many body fluids including saliva, mucus, and
tears are hostile to many microbes
•The low pH of skin and the digestive system
prevents growth of many bacteria
Cellular Innate Defenses
● Pathogens entering the mammalian body are subject to
phagocytosis
● Phagocytic cells recognize groups of pathogens by
TLRs, Toll-like receptors.
TLR Signaling
43.2
In adaptive immunity, receptors
provide pathogen-specific
recognition
Lymphocytes
● Lymphocytes are responsible for the
specificity of adaptive immune responses
● There are about 2 × 10^12 lymphocytes
in the human body, making the immune
system comparable in cell mass to the liver or brain
● Have cell-surface antigen receptors for foreign
molecules
● The response during its first encounter with an
antigen ensures that a more rapid and effective
response occurs on subsequent encounters with the
same antigen
Adaptive Immunity
● Adaptive immunity relies on lymphocytes that arise
from stem cells in the bone marrow and complete
their maturation in the bone marrow (B cells) or in
the thymus (T cells)
● Lymphocytes usually respond to foreign antigens
only if the innate immune system is first activated
● All receptor proteins on a single B or T cell are the
same, but there are millions of B and T cells in the
body that differ in the foreign molecules that their
receptors recognize
Antigen Recognition
● Each B cell antigen receptor
is a Y-shaped molecule
consisting of four polypeptide
chains-two identical heavy
and light chains
● For a T cell, the antigen
receptor consists of two
different polypeptide chains,
an alpha chain and a beta
chain, linked by a disulfide
bridge
Antigen Recognition Cont.
● Recognition of foreign molecules involves the
binding of variable regions of receptors to an
epitope-a small region of an antigen
● Antigen presentation- the display of the antigen
fragment in an exposed groove of the MHC
protein
Antigen Recognition
Animation
https://www.youtube.com/watch?v=GP5d7C
yU8WA
Section 43.3:
Adaptive Immunity Defends Against
Infection of Body Fluids and Body
Cells
Helper T Cells:
A Response to Nearly All Antigens
● Helper T cells trigger hormonal and cellmediated immune responses.
● Hormonal responses occur in blood and
lymph, antibodies help neutralize toxins and
pathogens.
● In cell-mediated immune responses, T
cells are specialized to destroy infected host
cells.
Activation
In order to activate a helper T cell:
● A foreign molecule must be present and it must bind to an
antigen receptor of the T cell.
● The antigen must be shown on the surface of an antigenpresenting cell. Antigen-presenting cell can be a
macrophage, B cell, or a dendritic cell.
● The protein CD4 binds to the class II MHC molecule, this
keeps the helper T cell bound to the antigen-presenting cell.
● The T cells are then able to secrete cytokines that stimulate
other lymphocytes
Cytotoxic T Cells
In the cell-mediated
immune response,
cytotoxic T cells are
effector cells. The
cytotoxic secretes a
protein that disrupts
the membrane integrity
and triggers apoptosis
B Cells and Antibodies
The hormonal response
when triggered, secretes
B Cells and Antibodies
B cells then secrete
plasma cells, the effector
cell of this process.
Different Ways Antibodies Work
Extras
● Active Immunization- develops naturally in
response to an infection. (vaccination)
● Passive Immunization- short immediate
protection
● Blood transfusions, organ transplants, etc.
can be rejected because of different MHC
molecules
Section 43.4
Disruptions in immune system function can elict
or exacerbate disease
Immune Diseases/Problems
● Allergies are exaggerated responses to
antigens known as allergens.
● In autoimmune diseases, the immune
system will lose tolerance on its body turn on
its molecules.
● Immunodeficiency is hereditary and
prevents proper functioning of different cell
defenses. (AIDS)
HIV and AIDS
● HIV affects helper T cells, the lose of these
cells affects hormonal and cell-mediated
responses leading to AIDS.
● HIV is able to escape the attention of the
immune system because of antigenic
variation and can be latent in the host DNA.
Sources
● http://www.ncbi.nlm.nih.gov/books/NBK26921/
● https://www.youtube.com/watch?v=GP5d7CyU8WA
● https://www.google.com/search?q=the+structure+of+a+
b+cell+antigen+receptor
● http://www.slideshare.net/jayswan/chapter-43-textbookpresentation?related=2