Transcript More than one mechanisms may be operating at a time!

Immune-Lymphatic System - 1
Introduction and Organisation
212 – 2005 – Week 8
Avinash Bharadwaj
Immunology : A vast and complex field
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Defence mechanisms of the body
Perspectives
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Emphasis : histological structure of lymphoid organs
Lecture 1 :
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Molecular
Cellular
Histological
Gross anatomical
Simple concepts
Lymphatic nodules, Tonsil, Lymph node
Lecture 2 :
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Spleen and Thymus
Further elaboration of immune processes
“Getting Rid Of ”…
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External attackers
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Viruses, bacteria, parasites…
Other “foreign” substances
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Particulate matter and chemicals
Our own dead cells
 Wayward cells
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An unfortunate sidelight – our own normal cells
Mechanisms
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Nonspecific defence
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Specific defence
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Cellular attack
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Molecular (“humoral”) attack
More than one mechanisms may be operating at a time!
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Cells involved
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White blood cells
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Macrophages
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Lymphocytes
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Others
Intricate interactions between cells – molecular messengers
WBCs – Quick Review
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Granulocytes
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Cytoplasmic granules 
Neutrophilic, eosinophilic or basophilic
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Agranulocytes
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Lymphocytes
Monocytes
Nonspecific Defence
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Neutrophils
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Movement out of capillaries
Phagocytosis and “digestion”
Expendable force
Action localised to site of infection
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Other granulocytes…
Specific Defence - Immunity
Recognition of “non-self” or “foreign”.
 Attack
 Memory
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Terminology
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Antigen – a foreign substance
Often (but not always) protein.
Antibody – a protein (γ-globulin) that specifically
combines with an antigen.
Recognition of Antigens
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The Antigen Presenting Cell
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Macrophage
Phagocytosis
Fragmentation of foreign material
Attachment to cell surface molecules (MHC)
MHC (Major Histocompatibility Complex)
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Proteins unique to each individual
(Originally recognised in the context of tissue
transplantation)
MHC Class I molecules present in all nucleated cells
MHC Class II – in APCs – Serve to bind antigens
Lymphocytes
Two major types – T and B lymphocytes
 Not distinguished by LM
 Two types of immune responses
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Cell mediated – direct attack by cells
 Humoral – antibodies as the medium
(Humor : fluid. Antibodies are transported by the blood and also
present in certain secretions))
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Cellular and Humoral Immunity
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“Cell mediated” immunity.
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Cytotoxic T cells – Perforin, Lympotoxin, TNF
Helper T cells
Suppressor T cells
Memory
Humoral immunity
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B lymphocytes  plasma cells (abundant rER)
Memory B cells
Helper T cells
Exposure and Barriers
External surface – skin
 The “open” systems
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Digestive and Respiratory systems – most exposed
Urogenital (to a lesser extent)
The epithelial barrier
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Integrity of epithelium
Intra-epithelial defence cells
Antibodies
“Local” infections and non-specific defence
 Beyond the barrier…
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Blood, Tissue Fluid and Lymph
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Blood capillaries
“Extravasation” of fluid
Tissue fluid and exchange
Not all the fluid returns to blood vessels.
Lymph flows through lymphatic vessels
before returning to larger veins.
Lymphoid (Lymphatic) Tissues
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Scattered lymphocytes and other cells
Lymphatic nodule – structural organisation
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Aggregates of lymphatic nodules
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Lymphocytes, macrophages, plasma cells, other leucocytes
Outer zone (corona) and germinal centre
Mucosa of GI Tract, respiratory system and other sites
Larger aggregates – Peyer’s patches (ileum), tonsillar
tissue.
Organised, encapsulated structures
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Lymph nodes
Spleen – special functions
Thymus – the academy
Lymphatic Nodule
“Non-capsulated”
 Single or aggregated
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parts of other lymphoid organs
 Outer dark zone
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(Corona or cap)
Germinal centre
Tonsils
A group of lymphoid structures
 Around the pharynx (GIT and RS)
 Lingual, “palatine”, tubal, nasopharyngeal
 Structurally similar
 Epithelium of the pharynx
 “Crypts”
 Lymphatic nodules
 Connective tissue and pharyngeal muscle.
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Peyer’s Patches
Ileum – “antimesenteric border”
 Lamina propria  submucosa
 Best seen in younger subjects
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Smaller aggregates present under
many mucous membranes :
“Mucosa Associated Lymphoid
Tissue” or MALT
Lymph Node
Capsulated
 Afferent lymphatics  “subcapsular sinus”
 Hilum – blood vessels, efferent lymphatic
 Cortex and medulla
 Cortex
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Lymphatic nodules, germinal centres
“Paracortex”
Medulla
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Medullary cords and sinusoids
C
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More next week!