Immune-Lymphatic System - 1 Introduction and Organisation 212 – 2005 – Week 8 Avinash Bharadwaj

Immunology : A vast and complex field  Defence mechanisms of the body  Perspectives  Molecular  Cellular  Histological  Gross anatomical  Emphasis : histological structure of lymphoid organs  Lecture 1 :  Simple concepts  Lymphatic nodules, Tonsil, Lymph node  Lecture 2 :  Spleen and Thymus  Further elaboration of immune processes

“Getting Rid Of ”…  External attackers  Viruses, bacteria, parasites…  Other “foreign” substances  Particulate matter and chemicals  Our own dead cells  Wayward cells  An unfortunate sidelight – our own normal cells

Mechanisms  Nonspecific defence  Specific defence  Cellular attack  Molecular (“humoral”) attack More than one mechanisms may be operating at a time!  Cells involved  White blood cells  Macrophages  Lymphocytes  Others  Intricate interactions between cells – molecular messengers

WBCs – Quick Review  Granulocytes  Cytoplasmic granules   Neutrophilic, eosinophilic or basophilic  Agranulocytes  Lymphocytes  Monocytes

Nonspecific Defence  Neutrophils  Movement out of capillaries  Phagocytosis and “digestion”  Expendable force  Action localised to site of infection  Other granulocytes…

Specific Defence - Immunity  Recognition of “non-self” or “foreign”.  Attack  Memory Terminology  Antigen – a foreign substance Often (but not always) protein.  Antibody – a protein (γ-globulin) that specifically combines with an antigen.

Recognition of Antigens  The Antigen Presenting Cell  Macrophage  Phagocytosis  Fragmentation of foreign material  Attachment to cell surface molecules (MHC)  MHC (Major Histocompatibility Complex)  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  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))

Cellular and Humoral Immunity  “Cell mediated” immunity.  Cytotoxic T cells – Perforin, Lympotoxin, TNF  Helper T cells  Suppressor T cells  Memory  Humoral immunity  B lymphocytes  plasma cells (abundant rER)  Memory B cells  Helper T cells

Exposure and Barriers  External surface – skin  The “open” systems  Digestive and Respiratory systems – most exposed  Urogenital (to a lesser extent)  The epithelial barrier  Integrity of epithelium  Intra-epithelial defence cells  Antibodies  “Local” infections and non-specific defence  Beyond the barrier…

Blood, Tissue Fluid and Lymph  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  Scattered lymphocytes and other cells  Lymphatic nodule – structural organisation  Lymphocytes, macrophages, plasma cells, other leucocytes  Outer zone (corona) and germinal centre  Aggregates of lymphatic nodules  Mucosa of GI Tract, respiratory system and other sites  Larger aggregates – Peyer’s patches (ileum), tonsillar tissue.  Organised, encapsulated structures  Lymph nodes  Spleen – special functions  Thymus – the academy

Lymphatic Nodule  “Non-capsulated”  Single or aggregated  Independent OR parts of other lymphoid organs  Outer dark zone  (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.

Peyer’s Patches  Ileum – “antimesenteric border”  Lamina propria  submucosa  Best seen in younger subjects Smaller aggregates present under many mucous membranes : “Mucosa Associated Lymphoid Tissue” or MALT

 Capsulated  Afferent lymphatics  “subcapsular sinus”  Hilum – blood vessels, efferent lymphatic  Cortex and medulla  Cortex  Lymphatic nodules, germinal centres  “Paracortex”  Medulla  Medullary cords and sinusoids Lymph Node

C M More next week!