Immune-Lymphatic System - 1 Introduction and Organisation 212 – 2004 – Week 8 Avinash Bharadwaj

Immunology Et cetera… Defence mechanisms of the body Perspectives Molecular Cellular Histological Gross anatomical

Immunology Et cetera… A vast and complex field Introduction and overview 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 Other “foreign” substances 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 Cells involved 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 Agranulocytes Cytoplasmic granules  Neutrophilic, eosinophilic or basophilic Agranulocytes Lymphocytes Monocytes

Nonspecific Defence Neutrophils Other granulocytes… 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))

T Lymphocytes “Cell mediated” immunity. Helper T cells Interleukins : relevant responses from other cells Cytotoxic T cells – Perforin, Lympotoxin, TNF Suppressor T cells – Interleukins control the reaction Memory

B Lymphocytes Humoral immunity Helper T cells Interleukins  activation – mitosis  large number of B cells against the same antigen. B lymphocytes  plasma cells (abundant rER) Antibodies work in various modes Memory B 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 Chemical factors 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), tonsilar tissue. Organised, encapsulated structures Lymph nodes Spleen – special functions Thymus – the academy

Lymphatic Nodule Outer dark zone (Corona or cap) Germinal centre

Tonsil A group of lymphoid structures Around the pharynx (GIT and RS) Lingual, “palatine”, tubal, nasopharyngeal Structurally similar

Palatine Tonsil Epithelium of the pharynx “Crypts” Lymphatic nodules Connective tissue and pharyngeal muscle.

Peyer’s Patches Ileum – “antimesenteric border” Lamina propria  submucosa

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

C M More next week!