Lymphatic (Immune) System Nestor T. Hilvano, M.D., M.P.H. (Images Copyright Discover Biology, 5 th 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 antigens inactivates antigens by Agglutination of microbes Precipitation of dissolved antigens Activation of the complement system Bacteria Antigen molecules Complement molecule 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_ Antigen- presenting cell Self-nonself complex T cell receptor Interleukin-1 stimulates the helper T cell Helper T cell Binding site for the antigen Binding site for the self protein Interleukin-2 stimulates cell division B cell Cytotoxic T cell Interleukin-2 activates B cells and 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 Sensitization: Initial exposure to an allergen Later exposure to the same allergen B cell (plasma cell) Antigenic determinant Mast cell Histamine An allergen (pollen grain) enters the bloodstream. B cells make antibodies. Antibodies attach to a mast cell. The allergen binds to antibodies on a mast cell. Histamine is released, causing allergy 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.