Lymphatic (Immune) System

Nestor T. Hilvano, M.D., M.P.H.(Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain,

Textbook, 2012.)

Learning Objectives 1. Define the following terms:

antigen, antibody, immunity, allergy, and inflammation.

2. Describe the components and main functions of the lymphatic system.

3. Discuss innate immunity against infections.

4. Differentiate the 2 main types of specific immunity. a) humoral immune system, b) cell- mediated immune system

5. Describe hypersensitivity reaction.

6. Discuss briefly disorders of the immune system.

Lymphatic (immune) System • Components

1. Lymph - clear colorless fluid similar to plasma, no cells except lymphocytes

2. Lymphatic vessels - carry lymph from peripheral tissues to veins

3. Lymphatic organs (lymph nodes, tonsils, thymus, spleen) & lymphatic tissues (appendix) - distributed throughout the body.

- Lymph nodes= widely

distributed, filters the lymph and

involve in immune response

Lymphatic (Immune) system • 2 Main Functions:1. To return excess fluid from the

interstitial fluid.2. To fight infection (Immunity)• Pathogens- agents causing a

disease• Antigen – molecule that elicits

an immune response• Antibody – protein to fight

against pathogens • 2 General Types of Defense:1. Nonspecific (innate)2. Specific (adaptive)

Nonspecific (Innate) immunity • Protective Barriers - Skin - Mucous membrane (lysozyme- antibacterial activity)

- Cilia and Mucus (sweep away particles/mucus trap materials and digest)

- Normal flora (normal bacteria to keep pathogens out)

- Phagocytosis by macrophages- Inflammation (release of histamine, increase blood flow, results to

heat, redness, swelling, and pain, tissue heals)

Red and white blood cells originate from pluripotent stem cells in the bone marrow.

These cells constantly divide and can differentiate into a variety of blood cells.

Specific Immunity

• Antibodies- proteins that binds to substances identified as nonself, to fight against it.

• T cell receptors- integral membrane proteins, recognize and bind nonself molecules on other cells, to fight against it.

• MHC (Major histocompatibility complex)- self-identifying labels on the surface of most mammalian cells (ME or NOT ME)

• Antigens- nonself molecules (foreign materials)

T cell receptors and antibodies bind to specific nonself molecules (antigens).

Specific sites on the antigens are called antigenic determinants or epitopes.

• Specificity - attack specific pathogens• Diversity - response to a wide variety of

pathogens• Ability to distinguish self from nonself• Memory - second exposure elicits faster

response to destroy pathogens

4 Key Traits of Specific Immunity

Specific Immunity: Humoral Immunity

• Humoral Immunity

- against antigens (bacteria and viruses) in the blood, lymph, & tissue fluids (interstitial fluid).

• Involves B cells to clone, differentiates into plasma cells which produce antibodies, that binds to pathogen

• Memory cells- involve in secondary immune response; rapid, more effective response to destroy antigen

• Mechanism of action:

- antigen-antibody reaction

Figure 24.9

Bacterium

Virus

Neutralization(blocks viral binding sites;

coats bacteria)

Binding of antibodies to antigensinactivates antigens by

Agglutinationof microbes

Precipitation ofdissolved antigens

Activation of thecomplement system

Bacteria

Antigenmolecules

Complementmolecule

Foreign cell Hole

Leads to

Cell lysis

Enhances

Phagocytosis

Macrophage

Specific Immunity: Cellular Immunity• Cellular Immunity

- T cell receptor recognizes antigens (bacteria and viruses inside body cells, fungi and protozoans, cancer cells and organ transplant)

• Involves T cells to clone itself to destroy cells infected by the virus directly or by lymphokines (proteins release by cytotoxic T cell)

• Cytotoxic T cell destroy foreign cells with MHC1 + antigen

• 3 types of T cells:- Cytotoxic T cells also called killer T cells. - helper T cells- suppressor T cells

Figure 24.11_2

32

4

5 6

7

Antigen-presentingcell

Self-nonselfcomplex T cell

receptor

Interleukin-1stimulates thehelper T cell

HelperT cell

Bindingsite for theantigen

Bindingsite for theself protein

Interleukin-2stimulatescell division

B cell

CytotoxicT cell

Interleukin-2activates B cellsand other T cells

Allergy • Sensitivities to antigens (allergens) in the

environment• Inflammatory response by release of histamine;

antigen-antibody reaction= Immediate response• T cell response= delayed response• Severe cases may result to anaphylactic shock

(Type I hypersensitivity reaction)- ex: acute attack of bronchial asthma, secondary to antibiotic allergy

• Type IV hypersensitivity reaction- delayed response; ex: skin test allergy

Figure 24.17

1 2 3 4 5

Sensitization: Initial exposure to an allergen Later exposure to the same allergen

B cell(plasma cell)

Antigenic determinant

Mastcell

Histamine

An allergen (pollengrain) enters thebloodstream.

B cells makeantibodies.

Antibodiesattach to amast cell.

The allergen bindsto antibodies ona mast cell.

Histamine isreleased, causingallergy symptoms.

Disorders • AIDS – kills helper T cells

• Autoimmunity – antibody against self; self-destruction

• Autoimmune disorders – turns against the self.

Rheumatoid Arthritis – antibody mediated damage

Insulin dependent diabetes – T cells attack pancreatic (beta) cells

Homework 1. Define terms: immunity, antigen, antibody, allergy,

specific immunity, autoimmunity, pathogen, and innate immunity.

2. Compare and contrast cellular immunity and humoral immunity.

3. Describe type I and type IV hypersensitivity.

4. List and describe the 3 types of T cells.

5. Name the components of the immune system.

6. What lymphoid organ is widely distributed in the body to filters the lymph?

7. Differentiate primary immune response from secondary immune response.