Lecture 16

Lymphatic System and Immune Response

Anatomy and PhysiologyJPHubbard

Hartnell College – Bio11

• Drain excess interstitial fluid & plasma proteins from tissue spaces

• Transport dietary lipids & vitamins from GI tract to the blood

• Produce, maintain and distribute lymphocytes

Components of Lymphatic System

• Lymph– similar to interstitial fluid

• Vessels– Blind ended

• Organs– red bone marrow– thymus– spleen– lymph nodes

• Diffuse Tissues– tonsils, adenoids &

peyers patches

Lymphatic Vessels• Capillaries – similar to veins

– Specialized to gather tissue fluid– In GI tract, known as lacteals -- contain chyle

• Drain through series of trunks to 2 ducts:– Right lymphatic duct: right side head, arm &

chest (above diaphragm)– Thoracic duct: Rest of body

Lymphedema: swelling and consequent distention of tissue to blockage of lymphatic vessel

Lymph Nodes– Fibrous connective covering = capsule– Fibrous partitions = Trabecula– Hilus: point of entry of blood vessels, efferent

lymphatic vessel– Afferent vessels enters opposite hilus through

cortex– Cortex and Medulla harbor various sorts of

immune cells – site of development of specific immune response

– Concentrated in different regions

Distribution of Lymph Nodes – major areas

• Cervical – head/neck

• Axillary – upper limbs, mammary in F.

• Popliteal – thigh and leg

• Inguinal – from lower limbs

• Thoracic – lungs, resp. and mediastinal strs.

• Also - Nodules: Associations with digestive tract/pharynx

Lymphatic Nodules

• scattered throughout connective tissue of mucous membranes = mucosa-associated lymphoid tissue (MALT)

• Peyer’s patches in the ileum of the small intestine

• Appendix

• Tonsils form ring at top of throat– adenoids (pharyngeal tonsil)– palatine tonsils (on each side wall)– lingual tonsil in the back of the tongue

Fig. 14.08

Other Lymphatic Organs• Spleen

– Lateral to stomach– Site of

• exposure of blood to populations of immune cells• Destruction of erythrocytes

• Thymus – superior to heart in mediastenum– Site of maturation and production of hormones

which stimulate maturation of T-lymphocytes – Decreases in mass after adolescence

Spleen

• Largest lymphoid organ in body

• The spleen serves two major functions in the body:

• 1. It is responsible for the destruction of old red blood cells (RBC)

• 2. It is a major site for mounting the immune response. The spleen behaves similarly to a lymph node but instead of filtering the lymphatic fluid it filters the blood.

Disease and Immunity• Pathogenesis: Process by which a pathogen

causes disease– Virus: Invade and subvert host cell metabolic

processes, damage cells– Bacteria, Fungi, Protozoans: Produce toxins,

direct tissue damage (enzymes)– Worms: release toxins, feed off blood, compete

with host for food– Prions: misfolding of host proteins

• Resistance: 2 levels– Innate/nonspecific– Adaptive/specific

Innate Defenses• Passive:

– Mechanical barriers– Chemical barriers

• Active:– Interferons – hormone-like produced in response

to virus infection– Fever– Inflammation– Defense cells

• Phagocytes– Neutrophils, monocytes – become active in tissues– Macrophages: fixed in certain organs

• Natural killer cells

Nonspecific Defenses – Surface Barriers

Natural Killer Cell at work – hole in cancer cell

Complement proteins (~ 20 different ones)• Stimulation

– Non-specific – by presence of foreign invader– Specifically – by interaction with antigen

specific antibodies

• Functions: – Stimulate histamine release– Promote phagocytosis– Kill bacteria through formation of membrane

attack complex– Enhance inflammation

Pathogen Specific Active Responses

• Two Important Characteristics:1. Specific

• Response to specific antigen or hapten

2. Memory• Basis for immunization

• Development of two cell lines– B-cell line– T-cell line

Two Cell Lines – Specific Response

• T-cells: produced bone marrow, mature in thymus–produce specific cytotoxic cells– like natural killer cells – but specific–Cell mediated response

• B-cells: produced/mature in bone marrow–specific antibodies (immunoglobulins)–Humoral response

Specificity

Body reacts to:• Antigens – a foreign substance

– Protein, Glycoprotein, smaller molecules (hapten) bound to larger molecules

• Toxins (poisons)• Molecules unique to microorganisms that are not associated

with human cells • Altered major histo-compatibility proteins (MHC protein)

identify self (‘Flag’ – friend/foe recognition)

– 10 million 1 billion different antigens may be recognized

• See: http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/prostruct/toll/toll.html

How the specific response is developed:

1. Antigen digested by macrophages / binds Virgin B cell

2. Macrophage

a. Acts as antigen presenting cell

b. Sends chemical signals which stimulate Helper T-cells division

3. Helper T cells + antigen (or antigen-MHC complex) activates multiplication of:

T cell line cytotoxic T cells

B cell line plasma cell

production of Memory B and T cell lines

Fig. 14.13

P371-372

Clonal Selection Theory

• Diverse B lymphocytes produced during fetal development– Body harbors diverse population of capable

of producing specific antibody w/o ever being exposed to particular antigen

• Encounter with antigen stimulates multiplication of specific cell line; a clone from ancestral cell– All descendents produce same antibody

Role of T cells in defending the body• Act like natural killer cells – but they are

specific• Act primarily on cells• Kill

– virus infected cells

– Cancer cells

– bacteria

Role of B cells in Defending Body• Produce antibodies – humoral response• Antibodies bind to foreign antigen

– either free or on cell surface

– Binding may destroy antigen directly, make it a better target for phagocytes

• Examples:– Toxins produced by pathogens

– Bind bacteria, fungi, protozoan pathogens

Antibodies

• 5 types – • IgG – main type of antibody involved in

response to disease – • Other types:• IgM – involved in activation of complement• IgA – certain secretions, protection of

digestive and resp. epith.

• IgD – found on surface of virgin B cells• IgE – association with mast cells – allergic

response and certain parasites

How your immune system ‘remembers’:• Two memory cell lines are produced:

– Memory T cells

– Memory B cells

• Long lived – ready to stimulate immune system to respond rapidly if the same pathogen shows up again– Produce effector B and T cell lines

Induced Immunity – Active vs. Passive

• Passive Immunity – occurs when individual given antibodies formed in another organism

• Active Immunity – results in activation of body to produce its own antibodies – B and T cell lines– Primary immune response –

• results in lower and transient titre• Important in elicitation of secondary response

Allergies - Immune System out of Control?

• Excess IgE antibodies produced • IgE antibodies bind to mast cells – • IgE antibodies interact with allergen

and release histamine• Histamine causes swelling of blood

vessels, fluid leakage• Type of response depends on where

reactions occur and degree of reaction

http://marie.guibert.chez.tiscali.fr/html/illsc.html

The End.