Biology 102
Fall 2001
R. Brundage
Lecture 1: Part IV
Immunity: Chapter 40
Ia.The Lymphatic System
A.Lymph Vascular System
1.The lymph vascular system includes lymph capillaries and lymph vessels.
a.It returns excess fluid (mostly water and called lymph) and
proteins that have leaked out of the blood capillaries.
b.It transports fats that are absorbed from the intestine.
c.It brings pathogens, foreign cells, and cellular debris to the
lymph nodes for disposal.
2.Lymph capillaries begin blindly in the tissues of the body; they lead to
lymph vessels, which in turn lead to ducts that return the fluid to the
bloodstream.
B.Lymphoid Organs and Tissues
1.The lymph nodes (containing lymphocytes, plasma cells, and
macrophages) are located along the lymph vessels; their resident cells help
remove bacteria and cellular debris from the lymph.
2.The spleen removes spent RBCs and holds macrophages and reserve
RBCs; it produces red blood cells in human embryos.
3.The thymus secretes hormones that regulate the activity of lymphocytes
and is a site where they multiply and mature.
Russian Roulette, Immunological Style
A.In 1796, Jenner demonstrated that inoculation with cowpox could protect against
smallpox.
B.Later, Pasteur developed similar vaccinations, which mobilized an immune
response.
C.Robert Koch was able to link a specific pathogenic microorganism to a specific
disease—anthrax.
I.Three Lines of Defense
A.Surface Barriers to Invasion [of pathogens]
1.Intact skin is an important barrier.
2.The normal microbial inhabitants of the gut, and vagina keep the growth
of pathogens in check.
3.Ciliated, mucous membranes in the respiratory tract sweep out bacteria
and particles.
4.Exocrine glands secrete lysozymes, which degrade the bacterial cell
wall.
5.Urine, with its low pH and flushing action, keep pathogens from the
urinary tract.
B.Nonspecific and Specific Responses
1.Phagocytic cells and antimicrobial substances are in place even before
pathogen invade.
2.Nonspecific responses are made by leukocytes and plasma proteins to
tissue damage in general; some pathogens are recognized by defenders
that can make a specific response.
II.Complement Proteins
A.The complement system is a set of plasma proteins that enhance nonspecific and
specific defenses.
B.About twenty kinds of complement proteins circulate in the blood in inactive form.
1.These proteins are activated in a cascading fashion when defenses are
breached.
2.Complement proteins assist is several ways:
a.Some form pore complexes which cause the pathogen to lyse and
die.
b.Some activated proteins promote inflammation.
c.Chemical gradients of proteins attract phagocytes to the scene and
encourage them to dine by coating the invader.
III.Inflammation
A.The Roles of Phagocytes and Their Kin
1.White blood cells, produced from stem cells in bone marrow, not only
circulate in blood and plasma, but also reside in lymph nodes, spleen,
liver, kidneys, etc. where they stand ready to defend.
2.Three kinds are swift to act but do not mount a sustained attack:
a.Neutrophils, the most abundant, phagocytize bacteria.
b.Eosinophils secrete enzymes that punch holes in parasitic
worms.
c.Basophils secrete histamine, which sustains inflammation.
3.Macrophages (formed from immature cells called monocytes) are slower
to act but can engulf and digest just about any foreign agent or damage
tissue.
B.The Inflammatory Response
1.Inflammatory response results include:
a.Localized warming and redness occur at the site of damage or
invasion.
b.Fluid seeps from blood vessels causing swelling and delivery of
infection-fighting proteins to the tissues.
c.Neutrophils and macrophages engulf foreign invaders and
debris.
d.Clotting mechanisms help wall off the pathogen and promote
repair of tissues.
2.While complement proteins are being activated, basophils and mast cells
secrete histamine, which promotes leakage of fluid out of capillaries.
3.Macrophages also secrete interleukins, which are communication signals
among white blood cells but in addition can signal the brain to reset its
thermostat" to cause a fever (not necessarily a bad thing).
IV.The Immune System
A.Defining Features
1.Physical barriers and inflammation may not be enough to check the
spread of an invader.
2.T and B lymphocytes of the vertebrate immune system are then called
upon.
a.Interactions among these cells are the basis of the vertebrate
immune system.
b.This system shows immunological specificity and memory.
3.Lymphocytes will ignore the "self" markers on the body’s own cells but
will respond to "nonself" markers (antigens) on foreign cells by dividing
rapidly to form huge populations of effector cells and memory cells.
B.Antigen-Presenting Cells—The Triggers for Immune Responses
1.Located on the membranes of the body’s cells are proteins called MHC
markers.
2.When an antigens enter the body, they are engulfed and destroyed by
macrophages but not completely—the antigen becomes attached to the
MHC marker to form an MHC-antigen complex, which is then displayed
on the macrophage’s surface.
3.Any cell that displays antigen with a suitable MHC marker is known as an
antigen-presenting cell and will be noticed by lymphocytes.
C.Key Players in Immune Responses
1.Helper T cells: recognize antigen-MHC complexes and respond by
secreting substances that promote the formation of large populations of
effector and memory cells.
2.Cytotoxic T cells: destroy infected (viruses for example)body cells and
tumor cells in what is referred to as cell-mediated immune responses.
3.B cells: and their progeny (effector cells) produce antibodies, which are
specific substances that tag targets for destruction; this is called the
antibody-mediated response.
D.Control of Immune Responses
1.When effector cells have reduced the antigen-bearing agents in the body,
the immune response slows and then stops.
2.Inhibitory signals from cells with repressor roles also help shut down
responses.