Lymphatic System and Immunity Chapter 22

Lymphatic System Functions: 1. Drain excess interstitial fluid. 2. Transporting dietary lipids 3. Protection against invasion by foreign chemicals and microorganisms

Lymphatic System Organs Lymphatic vessels Lymph

Lymphatic Capillaries Carry lymph from tissue spaces to lymphatic vessels (lymphatics) Lacteals - capillaries in intestine - digested fat absorbed into lymph Slightly larger diameter than blood vessels Interstial fluid flows in but not out

Lymph Trunks and Ducts

Lymph Forms by filtration Similar to plasma Large number of WBCs Few platelets Few RBCs and thrombocytes Low in protein concentration Contains little O2

Lymphatic vessels and lymph nodes Lymphatic Circulation capillaries Interstitial space Lymph capillary arteries Lymphatic vessels and lymph nodes heart Lymph trunk veins Lymph duct

Lymphatic Circulation

Lymphatic Organs Primary organs Secondary Organs/Tissues Red bone marrow Thymus Secondary Organs/Tissues Lymph nodes Spleen Lymphatic nodules

Thymus Behind sternum one of the central controls of the immunity system large in fetus and 0-2 yrs increases in size until adolescence; atrophies Produces lymphocytes (T-cells) and antibodies

Lymph nodes

Lymph nodes Filter lymph Quarantine noxious products Phagocytosis

Spleen Functions: 1. Blood destruction 2. Blood production 3. Immunologic function 4. Blood storage 5. Blood filtration 6. Phagocytize bacteria and old RBC

Lymphatic Nodules Concentrations of lymphatic tissue not surrounded by a capsule scattered throughout connective tissue of mucous membranes 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

Immune System Immunity: body’s ability to resist or eliminate potentially harmful foreign materials or abnormal cells Nonspecific immunity: nonselective protection Specific immunity: depends upon recognition of substance

Nonspecific Defenses (Innate Immunity) 1. Mechanical/Chemical barriers 2. Phagocytic Cells 3. Natural Killer (NK) cells 4. Inflammatory response 5. Complement system and Interferon

Mechanical/Chemical Barriers skin mucous membrane lacrimal apparatus sebum perspiration gastric juice

Phagocytic cells Macrophages (monocytes) fixed macrophage free macrophage Neutrophils

Natural Killer (NK) Cells kill a variety of microbes & tumor cells found in blood, spleen, lymph nodes & red marrow attack cells displaying abnormal MHC antigens

Inflammatory Response 1. Vasodilation - capillary permeability increased 2. Phagocytes activated 3. Tissue repair - clotting reaction walls off region - regional temperature increased

Complement 1. Destruction of bacterial cell walls 2. Inactivation of viruses 3. Stimulation of inflammation 4. Chemical attraction of phagocytes 5. Enhancement of phagocytic activity Complement

Interferon antiviral chemical produced by an infected host cell

Nonspecific Defenses (Innate Immunity)

Specific (Adaptive) Immunity 1. Antibody mediated (Humoral immunity): antibody or immunoglobulin production Cell-mediated immunity: cells directly attack

Clonal selection Process by which a lymphocyte proliferates and differentiates in response to a specific antigen Clone – population of identical cells all recognizing the same antigen as original cell Lymphocyte undergoes clonal selection to produce Effector cell – active helper T cell, active cytotoxic T cell, plasma cell, die after immune response Memory cell – do not participate in initial immune response, respond to 2nd invasion by proliferating and differentiating into more effector and memory cells, long life spans

Antigens Antigens have 2 characteristics Immunogenicity – ability to provoke immune response Reactivity – ability of antigen to react specifically with antibodies it provoked Entire microbes may act as antigen Typically, just certain small parts of large antigen molecule triggers response (epitope or antigenic determinant)

Major Histocompatibility Complex Antigens Self Antigens Major Histocompatibility Complex Antigens MHC or human leukocyte antigens (HLA) Normal function to help T cells recognize foreign or self Class I MHC (MHC-I) – built into all body cells except RBCs Class II MHC (MHC-II) – only on antigen presenting cells

Antigen Processing (Exogenous)

Antigen Processing (Endogenous)

Chemical Communication Cytokines Small protein hormones involved in immune responses Secreted by lymphocytes and antigen presenting cells

Cell-mediated immunity Formation of specially sensitized lymphocytes that have the capacity to attach to the foreign agent and destroy it. T cells helper T cells cytotoxic T cells memory T cells

Activation of Helper T Cells CD4 T cells Release cytokines which activate other immune cells

Activation of Cytotoxic T cells CD8 cells T cells Attack - cells infected by microbes - tumor cells - transplant tissue

Cytotoxic T Cell In action

Memory T Cells Available for swift response if a 2nd exposure to same foreign antigen should occur

Antibody-mediated immunity Humoral Immunity Antibody-mediated immunity antigen B Cell Plasma Cell Memory Cell Primary response Secondary response antibodies Plasma Cell

Activation of B Cells

Antibodies Immunoglobulins produced by plasma cells in response to an antigen Molecule consists of two parallel pairs of polypeptide chains Fixed segment - same for all antibodies in the same class and is responsible for type of antigen-antibody reaction Variable segment - antigen binding site; accounts for specificity

Antibody Structure

Antibody Diversity Immunoglobulin Classes IgG IgA IgM IgD IgE Immunoglobulin Classes

Immunoglobulin Classes

Antibody action Neutralizing antigen Immobilizing bacteria Agglutinating and precipitating antigen Enhancing phagocytosis Activating complement Defensive system of over 30 proteins Destroy microbes by causing phagocytosis, cytolysis, and inflammation Acts in a cascade – one reaction triggers another 3 different pathways ass activate C3 C3 then begins cascade that brings about phagocytosis, cytolysis, and inflammation

Immunological memory Thousands of memory cells exist after initial encounter with an antigen Next time antigen appears can proliferate and differentiate within hours Antibody titer measure of immunological memory Amount of Ab in serum Primary response Secondary response faster and stronger

Types of Acquired Immunity

Self-recognition and Self-tolerance Your T cells must have Self-recognition – be able to recognize your own MHC Self-tolerance – lack reactivity to peptide fragments from your own proteins Pre-T cells in thymus develop self-recognition via positive selection – cells that can’t recognize your own MHC undergo apoptosis Self-tolerance occurs through negative selection in which T and B cells that recognize self peptide fragments are eliminated Deletion – undergo apoptosis Anergy – remain alive but are unresponsive

Self-recognition and Self-tolerance

Homeostatic Imbalances of Immunity HIV

Homeostatic Imbalances of Immunity Allergic Reactions Autoimmune Diseases Infectious Mononucleosis Lymphomas Systemic lupus Erythematosus