The Lymphatic System and Immunity
An Overview of the Lymphatic System and Immunity
lymphatic system
The
lymphatic system
Contains
cells, tissues, and organs responsible for defending the body
Lymphocytes
resist infection and disease by responding to
Invading
pathogens such as bacteria or viruses
Abnormal
body cells such as cancer cells
Foreign
proteins such as toxins
Organization of the Lymphatic System
The lymphatic system consists of
Lymph
Lymphatic
vessels
Lymphoid
tissues and organs
Lymphocytes
and supporting phagocytic cells
Functions of lymphatic system
Primary
function is production, maintenance, and distribution of lymphocytes
Lymphocytes
must:
Detect
where problems exist
Be
able to reach the site of injury or infection
Lymphatic vessels include
Lymphatic
capillaries
Small
lymphatic vessels
Major
lymph-collecting vessels
Major lymph-collecting vessels
Superficial
and deep lymphatics
Thoracic
duct
Cisterna chyli
Right
lymphatic duct
Lymphocytes
Three
classes of lymphocytes
T
(thymus dependent) cells
B
(bone marrow-derived) cells
NK
(natural killer) cells
Lymphocyte production (lymphopoiesis)
Involves
bone marrow, thymus, and peripheral lymphoid tissue
B
cells and NK cells mature in bone marrow
T
cells mature in the thymus
Lymphoid tissue
Connective
tissue dominated by lymphocytes
Lymphoid
nodules
Lymphocytes
densely packed in areolar tissue
Found
in the respiratory, digestive, and urinary tracts
MALT (mucosa-associated lymphoid
tissue)
Collection
of lymphoid tissues linked with the digestive system
Lymphoid organs
Lymph
nodes function in the purification of lymph
Afferent
lymphatics carry lymph to nodes
Efferent
lymphatics carry lymph from nodes
Deep
cortex dominated by T cells
Outer
cortex and medulla contains B cells
The Lymphatic System
and Immunity
The Thymus
Located
behind sternum in anterior mediastinum
Capsule
Two
lobes
Divided
into lobules, each with a cortex and medulla
Cortical
lymphocytes surrounded by reticular endothelial cells
Maintain
bloodthymus barrier
Secretes
thymic hormones: thymosins,
thymopoietins, and thymulin
The Spleen
Largest
mass of lymphoid tissue
Cellular
components form pulp
Red
pulp contains RBC
White
pulp similar to lymphoid nodules
Spleen
functions include
Removal
of abnormal blood cells and other blood components
Storage
of iron
Initiation
of the specific immune response
Lymphatic system and body defenses
Nonspecific
defenses
Do
not distinguish one type of threat from another
7
types
Specific
defenses
Protect
against particular threats
Depend
upon the activation of lymphocytes
Nonspecific Defenses
Nonspecific Defenses, Physical barriers
Keep
hazardous organisms outside the body
Includes
hair, epithelia, secretions of integumentary and
digestive systems
(Part 1 - Physical Barriers)
Nonspecific Defenses, Phagocytes
Remove
cellular debris and respond to invasion by foreign pathogens
Monocyte-macrophage system - Fixed and free
Microphages
Neutrophils and eosinophils
Move
by diapedesis
Exhibit
chemotaxis
(Part 2 - Phagocytes)
Nonspecific Defenses, Immunological surveillance
Constant
monitoring of normal tissue by NK cells
NK
cells
Recognize
cell surface markers on foreign cells
Destroy
cells with foreign antigens
NK cell activation
Recognition
of unusual surface proteins
Rotation
of the Golgi toward the target cell and production of
perforins
Release
of perforins by exocytosis
Interaction
of perforins causing cell lysis
(Part 3 - Immunological Surveillance)
Nonspecific Defenses, Interferons
(cytokines)
Small
proteins released by virally infected cells
Trigger
the production of antiviral proteins
Three
major types of interferons are:
Alpha
produced by leukocytes and attract/stimulate NK cells
Beta
secreted by fibroblasts causing slow inflammation
Gamma
secreted by T cells and NK cells stimulate macrophage activity
(Part 4 - Interferons)
Nonspecific Defenses, Complement system
Cascade
of ~11 plasma complement proteins (C)
Destroy
target cell membranes
Stimulate
inflammation
Attract
phagocytes
Enhance
phagocytosis
Complement proteins interact with on another via two
pathways
Classical
Alternative
(Part 5 - Complement System)
Nonspecific Defenses, Inflammation
Localized
tissue response to injury producing
Swelling
Redness
Heat
Pain
Effects
of inflammation include
Temporary
repair of injury
Slowing
the spread of pathogens
Mobilization
of local, regional, and systemic defenses
(Part 6 - Inflammatory Response)
Nonspecific Defenses, Fever
Maintenance
of a body temperature above 37.2oC (99oF)
Pyrogens reset the hypothalamic thermostat and raise body
temperature
Pathogens,
toxins, antigen-antibody complexes can act as pyrogens
(Part 7 - Fever)
Specific Defenses
Forms of immunity
Innate
immunity
Genetically
determined
Present
at birth
Acquired
immunity
Not
present at birth
Achieved
by exposure to antigen
Active
immunity
Passive
immunity
Properties of immunity
Specificity
activated by and responds to a specific antigen
Versatility
is ready to confront any antigen at any time
Memory
remembers any antigen it has encountered
Tolerance
responds to foreign substances but ignores normal tissues
The immune system response
Antigen
triggers an immune response
Activates
T cells and B cells
T
cells are activated after phagocytes exposed to antigen
T
cells attack the antigen and stimulate B cells
Activated
B cells mature and produce antibody
Antibody
attacks antigen
T cells and Cell-mediated Immunity
Major types of T cells
Cytotoxic T cells (TC) attack foreign cells
Helper
T cells (TH) activate other T cells and B cells
Suppressor
T cells (TS) inhibit the activation of T and B cells
Antigen presentation
Antigen-glycoprotein
combination appears on a cell membrane
Called
MHC proteins (Major Histocompatibility Complex)
Coded
for by genes of the MHC
T-cells
sensitive to the antigen are activated upon contact
MHC classes
Class
I found on all nucleated cells
Class
II found on antigen presenting cells and lymphocytes
Lymphocytes respond to antigens bound to either class I
or class II MHC proteins
Antigen
recognition
T
cell membranes contain CD markers
CD3
markers present on all T cells
CD8
markers on cytotoxic and suppressor T cells
CD4
markers on helper T cells
Activation of CD8 cells
Responds
quickly giving rise to other T cells
Cytotoxic T cells seek out and destroy abnormal cells
lymphotoxin
Memory
TC cells function during a second exposure to antigen
Suppressor
T cells suppress the immune response
Activation of CD4 T cells by antigens presented on class
II MHC proteins
Produces
helper T cells and memory T cells
Activated
helper T cells
Secrete
lymphokines that coordinate specific and nonspecific
defenses
Enhance
nonspecific defenses
Stimulate
the activity of NK cells
Promote
activation of B cells
B Cells and Antibody-mediated Immunity
B cell sensitization of activation
Sensitization
the binding of antigens to the B cell membrane antibodies
Antigens
then displayed on B cell Class II MHC
TH
cells activated by same antigen stimulate B cell
Active
B cell differentiates into Memory B Cell or Plasma cell
Plasma
cells synthesize and release antibody
Antibodies structure
Antibodies
are Y-shaped proteins consisting of:
Two
parallel polypeptide chains
Heavy
chains and light chains
Constant
region and variable region
Antigen
binding site
Actions of antibodies include:
Neutralization
Agglutination
and precipitation
Activation
of complement
Attraction
of phagocytes
Opsinization
Stimulation
of inflammation
Prevention
of adhesion
Classes of Antibodies (immunoglobins)
IgG resistance against many viruses, bacteria and
bacterial toxins
IgE accelerates local inflammation
IgD found on the surface of B cells
IgM first type secreted after antigen arrives
IgA primarily found in glandular sec
Primary and secondary antibody response
Primary
response
Takes
about two weeks to develop
Produced
by plasma cells
Secondary
response
Rapid
increase in IgG
Maximum
antibody titer app
Focus on Hormones of the Immune System
Interleukins
Increase
T cell sensitivity
Stimulate
B cell activity, plasma formation, and antibody production
Enhance
nonspecific defenses
Moderate
the immune system
Interferons
Tumor
Necrosis Factors (TNFs) slow tumor growth
Colony
Stimulating Factors (CSFs)
Normal and Abnormal Resistance
Development of the Immune Response
Immunological
competence
The
ability to demonstrate an immune response after exposure to an antigen
Fetuses
receive immunity from the maternal bloodstream
Infants
acquire immunity following exposure
Immune disorders
Autoimmune
disorders
Immune
response mistakenly targets normal cells
Immunodeficiency
diseases
Immune
system does not develop properly or is blocked
Allergies
Inappropriate
or excessive immune response to allergens
Immediate
hypersensitivity (type I)
Cytotoxic reactions (type II)
Immune
complex disorders (type III)
Delayed
hypersensitivity (type IV)
Anaphylaxis
Circulating
allergen affects mast cells throughout body
Stress and the immune response
Interleukin-1
released by active macrophages
Triggers
release of ACTH resulting in glucocorticoid release
Moderates
the immune response
Lowers
resistance to disease
Stress can cause the following:
Depression
of the inflammatory response
Phagocytic reduction
Inhibition
of interleukin secretion
Aging and the Immune Response
With age
Immune
system becomes less effective
Increased
susceptibility to infection
Immune
surveillance declines