Transcript 5.2.05 Immune System

Lymphatic and Immune System
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Lymphatic Vessels
• The lymphatic vessels are similar in
structure and function to veins; movement
of lymph is dependent upon skeletal
muscle contraction, and internal valves
prevent backflow.
• Lacteals collect fat molecules at intestinal
villi and lymphatic capillaries collect excess
tissue fluid at blood capillaries.
• Tissue fluid becomes lymph once it enters
the lymphatic capillaries.
• Lymphatic capillaries merge to form larger
lymphatic vessels that carry lymph to the
subclavian veins.
• Edema is retention of fluids in the tissues
due to a blockage of the flow of lymph.
Lymphatic system
Lymphoid Organs
• Lymphoid organs include the lymph
nodes, tonsils, spleen, thymus gland, and
the red bone marrow.
• Lymph nodes are located at certain points
along lymphatic vessels and contain a
cortex and a medulla.
• The cortex contains nodules where
lymphocytes congregate when fighting off
a pathogen.
• Macrophages are concentrated in the
medulla where they work to cleanse the
lymph.
• Tonsils are patches of lymphatic tissue in
the pharynx; they are the first to encounter
pathogens in the nose and mouth.
• Tonsils perform functions similar to those
of the lymph nodes.
• The spleen cleanses blood of pathogens
and their toxins.
• The thymus is located behind the sternum
and is the site in which T lymphocytes
mature.
• The thymus produces the hormone
thymosin that appears to cause T
lymphocytes to mature; thymosin may play
other roles in immunity.
• The red bone marrow is the site where all
types of blood cells are produced by stem
cells.
• B lymphocytes mature in the red bone
marrow.
The lymphoid organs
Barriers to Entry
• Skin and mucous membranes lining the
respiratory, digestive and urinary tracts, oil
glands in the skin, ciliated cells that sweep
particles in mucus, and an acidic stomach
all contribute to keeping pathogens from
entering the body.
• Beneficial bacteria in the intestines and
vagina also prevent pathogens from taking
up residence.
Inflammatory Reaction
• The inflammatory reaction involves
redness, heat, swelling, and pain.
• The release of histamine and kinins from
damaged tissue cells and from mast cells
causes redness and swelling.
• The swollen area and kinins stimulate free
nerve endings, causing the sensation of
pain.
• Macrophages migrate to the site of injury
and can engulf pathogens and also
release colony-stimulating factors that
cause the bone marrow to release more
white blood cells.
• Anti-inflammatory drugs combat chronic
inflammation by acting against chemical
mediators released by white blood cells.
• The presence of pus indicates the body is
trying to overcome the infection.
Inflammatory reaction
Natural Killer Cells
• Natural killer cells kill virus-infected cells
and tumor cells by cell-to-cell contact.
• They are large, granular lymphocytes with
no specificity and no memory.
• Their number is not increased by prior
exposure to that kind of cell.
Protective Proteins
• The complement system, or complement,
refers to a number of plasma proteins that
assist nonspecific immunity.
• A small amount of activated complement
protein is needed to activate a cascade of
other proteins.
• Complement is activated when pathogens
enter the body.
• Complement amplifies the inflammatory
reaction by attracting phagocytes and
promoting phagocytosis.
• Some complement proteins join to form
pores in the surface of bacteria and cause
them to burst.
• Interferon is a protein produced by virusinfected cells that prepares non-infected
cells for attack and interferes with viral
replication; it is specific to species.
Action of the complement system
against a bacterium
• Specific defenses require B lymphocytes (B
cells) and T lymphocytes (T cells), which
are both produced in the bone marrow;
however, T cells mature in the thymus,
while B cells mature in bone marrow.
• B cells give rise to antibodies that are
shaped like antigen receptors and are
capable of combining with and neutralizing
antigens.
• T cells do not produce antibodies but
instead attack foreign antigens directly.
B Cells and Antibody-Mediated
Immunity
• A toxin is a chemical produced by certain
bacteria that is poisonous.
• As a B cell encounters a bacterial cell or a
toxin with a specific antigen in a lymph node
or spleen, it is activated to divide.
• The resulting cells are plasma cells, mature
B cells that mass-produce antibodies.
• Defense by B cells is thus called antibodymediated immunity.
• According to the clonal selection theory, it is
the antigen that selects which lymphocyte
will undergo clonal expansion, mass
producing lymphocytes bearing matching
antigen receptors.
• Some members of the clone become
memory B cells that remain in the body to
divide and produce more lymphocytes able
to secrete antibodies if the same antigen is
encountered at a later date.
• When infection passes, plasma cells
undergo apoptosis.
Clonal selection theory and B cells
Structure of IgG
• The most common type of antibody, the
IgG antibody, is a Y-shaped molecule that
has two binding sites for a specific
antigen.
• Antigen-antibody complexes often mark
the antigen for destruction by neutrophils
or macrophages, or they may activate
complement.
Structure of IgG
Other Types of Antibodies
• There are five types of antibodies:
• IgG – the main type in circulation, binds to
pathogens, activates complement, and
enhances phagocytosis
• IgM – the largest type in circulation,
activates complement and clumps cells
• IgA – found in saliva and milk, prevents
pathogens from attaching to epithelial cells
in digestive and respiratory tracts
• IgD – on surface of immature B cells, its
presence signifies the readiness of a B cell
• IgE – found as antigen receptor on
basophils in blood and on mast cells in
tissues, responsible for immediate allergic
response and protection against certain
parasitic worms.
• The different classes of antibodies vary in
structure.
T Cells and Cell-Mediated Immunity
• T cells mature in the thymus.
• Like B cells, each T cell bears a specific
receptor, however, for a T cell to recognize
an antigen, the antigen must be presented
by an antigen-presenting cell (APC).
• When a viral or cancer cell antigen is
presented, the antigen is first linked to a
major histocompatibility complex (MHC)
protein.
• Human MHC proteins are called HLA
(human lymphocyte-associated) antigens;
HLA antigens are self proteins that identify
tissues as belonging to the body (the basis
of tissue transplant rejection).
• Once a T cell’s antigen receptor matches up
to its specific antigen presented to it by a
macrophage (the APC), the T cell becomes
activated and secretes cytokines and
undergoes clonal expansion.
Clonal selection theory and T cells
Types of T Cells
• Cytotoxic T cells kill infected cells that bear
a foreign antigen on contact using perforin
molecules; cytotoxic T cells provide cellmediated immunity.
• Helper T cells stimulate other immune cells
and produce cytokines.
• Some T cells are memory T cells that will
jump-start an immune reaction upon reinfection.
Cell-mediated immunity
Active Immunity
• A person naturally develops active
immunity after infection.
• Immunization involves the use of vaccines,
substances that contain an antigen to
which the immune system responds.
• Vaccines are available to induce long-lived
active immunity in a well person.
• After exposure to a vaccine, which is a
non-virulent disease agent, antibodies are
produced.
• With a booster shot or second exposure,
the antibody titer rises to a much higher
level.
• Active immunity is long-lived because
there are memory B cells and memory T
cells that will respond to lower doses of
antigen in the body.
Active immunity due to
immunizations
Passive Immunity
• Passive immunity occurs when an
individual is given prepared antibodies.
• For example, a newborn has antibodies
that passed from its mother through the
placenta.
• Breast-feeding passes antibodies from
mother to child.
• However, passive immunity is short-lived
since the antibodies were not produced by
the person’s own B cells.
Passive immunity
Cytokines and Immunity
• Cytokines are signaling molecules
produced by T lymphocytes, monocytes,
and other cells.
• Both interferon and interleukins are
cytokines used to improve a person’s own
T cell performance in fighting cancer.
• Interleukins show promise in the treatment
of chronic infectious diseases.
Monoclonal Antibodies
• All plasma cells derived from the same B
cell secrete an identical antibody.
• B lymphocytes can therefore be exposed
to a particular antigen and will produce
monoclonal antibodies to the specific
antigen.
• Activated B lymphocytes are fused with
myeloma cells and these hybridomas
produce only one type of antibody.
Production of monoclonal
antibodies
Allergies
• Allergies are hypersensitivities to
substances such as pollen or animal
dander that are normally not harmful.
• Weak antigens such as these are called
allergens.
• The response itself can cause some
degree of tissue damage.
Immediate Allergic Response
• An immediate allergic response can occur
within seconds after contacting an antigen.
• Anaphylactic shock is a severe reaction
characterized by a sudden life-threatening
drop in blood pressure.
• Immediate allergic responses are caused by
IgE antibodies attaching to mast cells and
basophils; these cells then release histamine
which causes the symptoms of allergies,
some of which are severe.
Delayed Allergic Response
• Delayed allergic responses are started by
memory T cells at the site of the allergen.
• The response is regulated by cytokines
secreted by T cells and macrophages.
• Examples of delayed allergic responses
include the skin test for tuberculosis and
contact dermatitis from poison ivy, jewelry,
and other possible irritants.
Blood-Type Reactions
• Illness and death sometimes resulted from
the first attempts at blood transfusions.
• It was later discovered that only certain
types of blood are compatible because red
blood cell membranes carry proteins or
sugar residues that are antigenic to
recipients.
• The ABO blood system represents a series
of antigens on red blood cells that denote
blood type.
ABO System
• The ABO blood typing system is based on
the presence of two antigens on the surface
of red blood cells; antigen A and antigen B.
• Blood types include A, B, or AB, or type O,
which has no antigens.
• In the plasma there are two possible
naturally-occurring antibodies: anti-A and
anti-B.
• If the corresponding antigen and antibody
are put together, clumping, or
agglutination, occurs; in this way the blood
type of the individual may be determined.
Blood typing
Rh System
• The Rh factor is also a blood type; a
person with this antigen on their red blood
cells is Rh positive (Rh+); those without it
are Rh negative (Rh-).
• Rh factor is important during pregnancy
because an Rh- mother may form
antibodies to the Rh antigen during the
pregnancy or at the birth of a child who is
Rh+.
• These antibodies can cross the placenta
to destroy the red blood cells of any
subsequent Rh+ child, causing hemolytic
disease of the newborn.
• A Rho-Gam injection uses anti-Rh
antibodies to attack Rh+ cells before they
can stimulate the mother to produce her
own antibodies.
Hemolytic disease of the newborn
Tissue Rejection
• Tissue rejection occurs when cytotoxic T
cells bring about the destruction of foreign
tissue in the body.
• A close match between donor and
recipient can reduce rejection.
• Immunosuppressive drugs act by inhibiting
the response of T cells to cytokines, but
can result in kidney damage.
Autoimmune Diseases
• Autoimmune disease occurs when
cytotoxic T cells or antibodies mistakenly
attack the body’s own cells as if they bear
foreign antigens.
• Autoimmune diseases include: myasthenia
gravis, multiple sclerosis, systemic lupus
erythematosus, and rheumatoid arthritis.
• It has been suggested that type I diabetes
and heart damage after rheumatic fever
are autoimmune diseases.
• Immunity consists of nonspecific and
specific defenses to protect against
disease.
• Nonspecific defenses consist of barriers to
entry, the inflammatory reaction, natural
killer cells, and protective proteins.
• Specific defenses involve two types of
lymphocytes: B lymphocytes and T
lymphocytes.
• Medically induced immunity involves use
of vaccines to achieve long-lasting
immunity and use of antibodies to provide
temporary immunity.
• While immunity protects us, it is also
responsible for undesirable effects, such
as allergies, autoimmune diseases, and
tissue rejection.
Ex 23: Arthropods!
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Evolutionary tree
Arthropods
• Arthropods are the most varied and
numerous of animals.
• The success of arthropods is largely
attributable to a flexible exoskeleton, jointed
appendages, and specialization of body
regions.
• Three body regions – head, thorax, and
abdomen – with specialized appendages in
each region, and a well-developed nervous
system characterize this group.
Arthropod diversity
Crustaceans
• Crustaceans are largely marine and have
a head that bears compound eyes, two pair
of antennae, and specialized mouth parts.
• Five pairs of walking legs include a first pair
of pinching claws.
• In the crayfish, head and thorax are fused
into a cephalothorax which is covered on
the top and sides by carapace.
• The abdominal segments have
swimmerets.
• The crayfish has an open circulatory
system in which the heart pumps blood
into a hemocoel consisting of sinuses
where the hemolymph flows about the
organs.
• Respiration takes place by gills under the
hard carapace, and there is a ventral solid
nerve cord.
• Sexes are separate in the crayfish.
Male crayfish, Cambarus
Insects
• The head of an insect usually bears a pair
of antennae, compound eyes, and simple
eyes.
• The thorax bears three pairs of legs and
up to two pairs of wings, and the abdomen
contains most of the internal organs.
• The insect exoskeleton is lighter and
contains less chitin than that of many other
arthropods.
Insect diversity
• Grasshoppers are examples of insects
adapted to a terrestrial life; they respire by
tracheae and have wings that allow them to
evade enemies; the third pair of legs is
suitable for jumping.
• There is a tympanum for the reception of
sound waves and a male penis for passing
sperm to the female without desiccation.
• Malpighian tubules function in excretion in
grasshopper.
• Grasshoppers undergo gradual
metamorphosis from nymph to adult.
• Butterflies undergo complete
metamorphosis, changing from larva to
pupa to adult.
Female grasshopper
Arachnids
• The arachnids include terrestrial spiders,
scorpions, ticks, and mites.
• The cephalothorax bears six pairs of
appendages: the chelicerae and the
pedipalps, and four pairs of walking legs.
• Scorpions are the oldest terrestrial
arthropods.
• Ticks and mites are parasitic.
• Spiders are well-adapted to life on land
and have Malphigian tubules – they
secrete uric acid, helping to conserve
water.
• Spiders spin silk used in various ways.
• Where spiders spin webs, the type of web
is a feature that demonstrates the
evolutionary relationship among spiders.
Arachnid diversity
Lab Ex 24: Echinodermata
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Evolutionary tree
Echinoderms
• Echinoderms and chordates are
deuterostomes.
• In deuterostomes, the second embryonic
opening becomes the mouth and a coelom
forms by outpocketing of the primitive gut
making these animals enterocoelomates.
• A dipleurula larva is found among some.
Characteristics of Echinoderms
• Echinoderms are a diverse group of
marine animals; there are no terrestrial
echinoderms.
• They have an endoskeleton consisting of
spine-bearing, calcium-rich plates.
• Echinoderms are often radially
symmetrical, although the larva is a freeswimming filter feeder with bilateral
symmetry.
• Echinoderm Diversity
• Echinoderms include:
• Sea lilies (class Crinoidea)
• Sea cucumbers (class Holothuroidea)
• Brittle stars (class Ophiuroidea)
• Sea urchins and sand dollars (class
Echinoidea)
• Sea stars (class Asteroidea)
Echinoderm diversity
• Sea Stars
• Sea stars are an example of echinoderms
and possess tiny skin gills, a central nerve
ring with branches, and a water vascular
system for locomotion.
• Water enters this system through the sieve
plate, passes into a ring canal, then into
ampullae, and into tube feet; expansion and
contraction of tube feet move the sea star
along.
• Each of the five arms contains branches
from the nervous, digestive, and
reproductive systems.
• When a sea star eats a bivalve, it everts
its cardiac stomach into the bivalve and
secretes enzymes; partially digested food
is taken into the sea star.
• Echinoderms do not have a respiratory,
circulatory, or excretory system.
• The water vascular system carries out
these functions.
• Sea stars reproduce both sexually, and
asexually by fragmentation.
Sea star anatomy and behavior