The Lymphatic System and
Immunity
Lymph, lymph capillaries, ducts,
nodes and other lymphoid organs
Functions
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Filter and absorb excess tissue fluid and
return it back into circulation
Transport of dietary lipids via lacteals
Carry out immune responses
Lymph and Lymph Capillaries
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Lymph - clear, watery fluid resembling
interstitial fluid
Lymph capillaries - begin as blind-ended
capillaries consisting of simple
squamous epithelium allowing one-way
movement of fluid
Lymph Vessels
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Formed from merging capillaries
Have thin walls and posses valves
Thoracic duct originates as cisterna
chyli draining abdomen, extremities,
and left side of body
Right lymphatic duct - drains lymph
from the right arm and upper right side
of body
Elephantiasis
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Blockage of the lymphatic system by
parasitic worms
Transmitted by mosquitos
Causes severe swelling
Lymph nodes
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Oval structures clustered along
lymphatic vessels that serve to filter
lymph
Consists of capsule, cortex, and medulla
Cortex contains mostly lymphocytes
Medulla filled with macrophages
Accessory Structures
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Spleen
Thymus
Tonsils
 pharyngeal
 palatine
 lingual
Spleen
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Size of a fist
Located in left superior abdominal cavity
Functions:
 Lymphocyte storage & surveillance
 Blood cleansing
 Recycles blood products
 Fetal erythrocyte production
 Stores blood platelets
Thymus
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Located in lower neck, upper thoracic
region
Secretes hormones, thymosin &
thymopoietin
Function: T-cell maturation
Decreases in size with age
Tonsils
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Form ring around entrance to throat
Epithelial surface invaginates to form crypts
that trap bacteria & particulate matter
Types:
 Palatine tonsils - visible tonsils
 Pharyngeal tonsil (adenoids)
 Lingual tonsil - at base of tongue
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Tubal tonsils - surround the openings to the
auditory tubes
Other aggregates of lymphoid
tissue
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Peyer’s patches - nodules located in the
ileum portion of the small intestine
Appendix
Destroy bacteria in the digestive system
Belong to MALT (Mucosa-Associated
Lymphatic Tissue
Disorders of the Lymphatic
System
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Hodgkin’s disease - malignant cancer of the
lymph nodes
Lymphoma - any tumor of the lymphoid
tissue (benign or malignant)
Non-Hodgkin’s lymphoma - all cancers of
lymphoid tissues except Hodgkin’s disease
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Tonsilitis - inflammation of the tonsils
Mononucleosis - caused by Epstein-barr
virus attacking the B-lymphocytes which
are in turn attacked by oversized Tlymphocytes. These were misidentified
orginally as monocytes.
Nonspecific Resistance
Mechanical Barriers
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Skin - epidermis
Mucous membranes
Cilia - hair, mucus
Flushing mechanisms
Chemical Protection
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Lysozymes - in tears & saliva
Sebum Gastric juice
Body secretions 
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Acid = pH 3-5
Mucus
Antimicrobial substances
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Interferons
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defend against viruses, suppress tumors and
enhance phagocytosis;
stimulates production of PKR which interferes with
viral replication
Complement
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>20 proteins that attach and “lyse” the cell
opsonization (enhances phagocytosis)
enhances the inflammatory response
Non-specific Immunity
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Phagocytosis
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Macrophages, Neutrophils
chemotaxis, adherence, ingestion, destroy
Natural Killer Cells (NK)
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Large granular lymphocytes
Attach and release “perforins”
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Inflammation
 swelling, redness, pain, heat
 histamines = promote dilation & permeability
Phagocyte mobilization
 Leukocytosis leukocyte production
 Margination - neutrophils collect inside
nearby capillaries
 Diapedesis - neutrophils squeeze out of
capillaries into tissues
 Chemotaxis - neutrophils are attracted to
injury
 Monocytes follow; become Macrophages
Fever
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Pyrogens released by leukocytes &
macrophages raise body temperature
Inhibits growth of microorganisms
Increases metabolic rate of cells
Can denature enzymes
Specific Immunity
Characteristics: specificity
memory
self recognition
Types of Cells
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Lymphocytes arise from hemocytoblasts
in the bone marrow
B cells develop immunocompetence in
the bone marrow
T cells - mature in thymus
Types of Immunity
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Antibody-mediated immunity
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humoral immunity
involves B cells and the production of
antibodies
Cell - mediated immunity
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cellular immunity
involves the destruction of intracellular
pathogens by T cells
Antigens
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Any substance that can elicit an immune
response
Immunogenicity - “antibody-generating”
Haptens - incomplete antigens (allergens)
Major histocompatibility complex antigens
(MHC-I, MHC-II) ; “Self”-proteins
Class I - found on all cells
Class II - found only on certain cells
Antibodies = immunoglobulins
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Highly specific soluble proteins secreted by
plasma cells in response to an antigen
Structure of an antibody
 Heavy and light chains
 Variable and constant regions
 Up to a Billion different variables
 Antigen-binding sites
Antibodies
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Five classes of antibodies
IgM - first released; can fix complement
 IgA - usually found in secretions
 IgD - B-cell receptor
 IgG - most abundant; crosses placenta;
can fix complement
 IgE - causes allergic reactions
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Antibody - Mediated Immunity
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B cells are activated by the presence of a
foreign antigen which is taken into the B cell,
processed and then displayed in combination
with an MHC-II molecule the on the cell’s
surface
Activated B cells develop into clones of
antibody producing plasma cells
Plasma cells produce antibodies (2,000/sec)
Costimulation by Helper T cells useful
Functions of Antibodies
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Agglutination
Precipitation
Neutralization
Enhanced phagocytosis
Complement activation
Immunological Memory
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Primary response - first exposure
Secondary response - 2nd, 3rd, 4th, etc.
 Faster
 Higher Levels
 More efficient
Active & Passive Immunity
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Active = caused by encounter with antigens
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Natural - acquired by infection & disease
Artificial - acquired by vaccination
Passive = caused by encounter with
antibodies
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Natural - acquired from Mom; antibodies cross
placenta
Artificial - acquired from immune sera such as:
gamma globulin, antivenom, antitoxins
Cell - Mediated Immunity
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T cells recognize and respond only to
processed antigen presented by an APC
(antigen presenting cell)
Binding of T cell to macrophage causes
secretion of interleukin-I which helps activate
T helper cells (also called CD4 or T4 cells)
TH cells secrete IL-2 which enhances B cell
activity and costimulates cytotoxic T cells
(CD8 or T8 cells)
Types of Lymphocytes
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Helper T cells - TH
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Cytotoxic (killer)T cells - T8
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Stimulates macrophages
Suppressor T cells - TS
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Kills invaded cells, cancer cells, rejects tissue
Delayed Hypersensitivity T cells - TDH
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Stimulates other B & T cells (co-stimulation)
Slows or stops B & T cells
Memory T cells
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remain in body for years for secondary response
Cytokines
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Interferons
Interleukins
Lymphotoxins
Macrophage migration inhibitory factor
Perforins
Supressor factors
Complement
Immunodeficiencies
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SCID - Severe Combined Immunodeficiency
Syndrome
Acquired Immunodeficiencies
 Disease induced; Hodgkins, Leukemia
 Chemically induced; immune suppressing
drugs
 AIDS
 Diagnosed 1981; Began ?
AutoImmune Disorders
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Multiple Sclerosis - affects white matter of CNS
Myasthenia Gravis - destroys Ach receptors
between nerves & muscles
Graves’ Disease - causes hyperthyroidism
Type I Juvenile Diabetes - destroys insulinproducing cells
Systemic Lupus Erythematosus Rheumatoid Arthritis - attacks joint tissues