The Lymphatic System and Immunity

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The Lymphatic System and Immunity

• Lymph, lymph capillaries, ducts, nodes and other
  lymphoid organs

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Functions

• Filter and absorb excess tissue fluid and return
  it back into circulation
• Transport of dietary lipids via lacteals
• Carry out immune responses

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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

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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

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Elephantiasis

• Blockage of the lymphatic system by parasitic
  worms
• Transmitted by mosquitos
• Causes severe swelling

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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

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Accessory Structures

• Spleen
• Thymus
• Tonsils
• pharyngeal
• palatine
• lingual

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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

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Thymus

• Located in lower neck, upper thoracic region
• Secretes hormones, thymosin thymopoietin
• Function T-cell maturation
• Decreases in size with age

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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

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Other aggregates of lymphoid tissue

• Peyers 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

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Disorders of the Lymphatic System

• Hodgkins disease - malignant cancer of the lymph
  nodes
• Lymphoma - any tumor of the lymphoid tissue
  (benign or malignant)
• Non-Hodgkins lymphoma - all cancers of lymphoid
  tissues except Hodgkins disease

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• 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.

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Nonspecific Resistance
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Mechanical Barriers

• Skin - epidermis
• Mucous membranes
• Cilia - hair, mucus
• Flushing mechanisms

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Chemical Protection

• Lysozymes - in tears saliva
• Sebum -
• Gastric juice
• Body secretions -
• Acid pH 3-5
• Mucus

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Antimicrobial substances

• Interferons
• defend against viruses, suppress tumors and
  enhance phagocytosis
• stimulates production of PKR which interferes
  with viral replication
• Complement
• gt20 proteins that attach and lyse the cell
• opsonization (enhances phagocytosis)
• enhances the inflammatory response

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Non-specific Immunity

• Phagocytosis
• Macrophages, Neutrophils
• chemotaxis, adherence, ingestion, destroy
• Natural Killer Cells (NK)
• Large granular lymphocytes
• Attach and release perforins

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• 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

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Fever

• Pyrogens released by leukocytes macrophages
  raise body temperature
• Inhibits growth of microorganisms
• Increases metabolic rate of cells
• Can denature enzymes

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Specific Immunity

• Characteristics specificity
• memory
• self recognition

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Types of Cells

• Lymphocytes arise from hemocytoblasts in the bone
  marrow
• B cells develop immunocompetence in the bone
  marrow
• T cells - mature in thymus

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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

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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

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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

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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

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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 cells 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

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Functions of Antibodies

• Agglutination
• Precipitation
• Neutralization
• Enhanced phagocytosis
• Complement activation

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Immunological Memory

• Primary response - first exposure
• Secondary response - 2nd, 3rd, 4th, etc.
• Faster
• Higher Levels
• More efficient

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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

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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)

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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

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Cytokines

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

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Immunodeficiencies

• SCID - Severe Combined Immunodeficiency Syndrome
• Acquired Immunodeficiencies
• Disease induced Hodgkins, Leukemia
• Chemically induced immune suppressing drugs
• AIDS
• Diagnosed 1981 Began ?

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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