The Lymphatic System and

Immunity

Lymph, lymph capillaries, ducts, nodes and other

lymphoid organs

Functions 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 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 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 Blockage of the lymphatic system by

parasitic worms Transmitted by mosquitos Causes severe swelling

Lymph nodes 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 Spleen Thymus Tonsils

pharyngeal palatine lingual

Spleen

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 Located in lower neck, upper

thoracic region Secretes hormones, thymosin &

thymopoietin Function: T-cell maturation Decreases in size with age

Tonsils 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

Tubal tonsils - surround the openings to the auditory tubes

Other aggregates of lymphoid tissue 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

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

Tonsilitis - inflammation of the tonsils Mononucleosis - caused by Epstein-

barr virus attacking the B-lymphocytes which are in turn attacked by oversized T-lymphocytes. These were misidentified orginally as monocytes.

Nonspecific Resistance

Mechanical Barriers Skin - epidermis Mucous membranes Cilia - hair, mucus Flushing mechanisms

Chemical Protection Lysozymes - in tears & saliva Sebum - Gastric juice Body secretions -

Acid = pH 3-5 Mucus

Antimicrobial substances Interferons

defend against viruses, suppress tumors and enhance phagocytosis;

stimulates production of PKR which interferes with viral replication

Complement >20 proteins that attach and “lyse” the cell opsonization (enhances phagocytosis) enhances the inflammatory response

Non-specific Immunity Phagocytosis

Macrophages, Neutrophils chemotaxis, adherence, ingestion,

destroy Natural Killer Cells (NK)

Large granular lymphocytes Attach and release “perforins”

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 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 Lymphocytes arise from

hemocytoblasts in the bone marrow

B cells develop immunocompetence in the bone marrow

T cells - mature in thymus

Types of Immunity Antibody-mediated immunity

humoral immunity involves B cells and the production of

antibodies Cell - mediated immunity

cellular immunity involves the destruction of

intracellular pathogens by T cells

Antigens 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

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 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

Antibody - Mediated Immunity

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 Agglutination Precipitation Neutralization Enhanced phagocytosis Complement activation

Immunological Memory Primary response - first exposure Secondary response - 2nd, 3rd, 4th,

etc. Faster Higher Levels More efficient

Active & Passive Immunity Active = caused by encounter with

antigens Natural - acquired by infection & disease Artificial - acquired by vaccination

Passive = caused by encounter with antibodies Natural - acquired from Mom; antibodies

cross placenta Artificial - acquired from immune sera such

as: gamma globulin, antivenom, antitoxins

Cell - Mediated Immunity 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

Helper T cells - TH

Stimulates other B & T cells (co-stimulation) Cytotoxic (killer)T cells - T8

Kills invaded cells, cancer cells, rejects tissue Delayed Hypersensitivity T cells - TDH

Stimulates macrophages Suppressor T cells - TS

Slows or stops B & T cells Memory T cells

remain in body for years for secondary response

Cytokines Interferons Interleukins Lymphotoxins Macrophage migration inhibitory factor Perforins Supressor factors Complement

Immunodeficiencies SCID - Severe Combined

Immunodeficiency Syndrome Acquired Immunodeficiencies

Disease induced; Hodgkins, Leukemia Chemically induced; immune

suppressing drugs AIDS

Diagnosed 1981; Began ?

AutoImmune Disorders Multiple Sclerosis - affects white matter of

CNS Myasthenia Gravis - destroys Ach

receptors between nerves & muscles Graves’ Disease - causes hyperthyroidism Type I Juvenile Diabetes - destroys insulin-

producing cells Systemic Lupus Erythematosus - Rheumatoid Arthritis - attacks joint tissues